Chapter-IV

Spectroscopic properties of

Sm3+ and V4+ ions in

Na2O-SiO2-ZrO2 glasses

Published in Journal of Molecular Structure

1054–1055 (2013) 339–348

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Spectroscopic properties of Sm3+ and V4+ ions in Na2O-SiO2-ZrO2 glasses

4.1 Introduction

The study of oxide glasses with rare earth ion is of great importance

due to the wide range of applications in sensiting solid state and glass

lasers, optical fiber and optical detectors for fluorescent display devices.

Due to these optical properties Sm3+ ions in the glass network may change

the chemical environment. They have high emissions efficiency to

recognize the spectral properties helpful to design of new glass composition

for photonic materials [1-5]. Sm3+ doped laser materials are of interest

in lasers for next generation nuclear fusion [6]. These materials can

be used as a gain media in the microchip laser at high doping levels

since this rare earth ion has a very simple energy level scheme with

desirable properties for a laser system. The Sm3+ doped laser materials

have several advantages (compared to other rare-earth ions doped laser

materials) such as weak concentration quenching effect, no excited

state absorption, no upconversion losses, low quantum defect and

thermal load since there is lack of high lying excited states. It was

reported that Sm3+ gives out high luminescence output in NIR region

and exhibit lifetime (of the order of ms) when compared with those

of other rare earth ions of the same host medium is considered for

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both ions. Considerable recent studies are available on NIR

luminescence emission of Sm3+ ion in a variety of glass hosts [7-9].

The presence of alkali oxides like sodium act like a network modifier in the

glass network enhancing the rare earth suitability of the glasses to produce

non bridging oxygen atoms (NBO) that helps in the design of high

efficiency in short length fiber amplifiers [10-13]. Silicate, known as a

glass forming oxide enters in to alkali metal oxide in glass matrix

eventually changes the glass network leading to the formation of non

bridging oxygen atoms. Silicate has its applications in different areas of

electronics and other fields due to high chemical resistance, coefficient of

thermal expansion and good UV transparency [14-16]. silicate glasses to

offer suitable environment for hosting Sm3+ ion to give out high

luminescence efficiency in the visible and NIR regions.

Zirconium oxide is one of the intermediate oxides that enters the

sodium silicate glasses and improves the transparency, electrical resistivity,

chemical inertness. This results in hike of the refractive index, decreases in

the cutoff wavelength and reduction photochromism of the glasses and

helps to improve the optical and mechanical properties [17-21]. Transition

metal oxides (TMOs) exhibit a rich collection of interesting and intriguing

properties, which can be tailored for a wide variety of applications

including low-loss power delivery, quantum computing using cooper pairs,

ultra high-density magnetic data storage and more recently spintronic

~ 210 ~

applications. Many transition metal oxides have been prepared in bulk form

or as thin films, which paved the way for intensive research studies in the

past several decades. Among this vanadium is one the transition metal

oxide that displays excellent properties of electrochromisim of blue

green yellow and has unique properties because of its semiconducting

properties that is the result of electron hopping between the ions. Vanadium

exists in three possible oxidation states i.e. V3+, V4+ and V5+. The V2O5 can

be incorporated in the rare earth glasses it undergoes radiative and non

radiative transitions are takes place with in glass matrix. Due to this the

energy transfer process increases the laser efficiency of the glasses and also

has significant applications in research and development of new laser

materials [22-29]. Keeping in view of the above interesting results, the

present work makes a quantitative evaluation of the radiative and non

radiative energy transfer in the Sm2O3:V2O5 codoped sodium silicon

zirconium (NSZ) glasses are used for the present study.

In the present study the spectroscopic characteristics of Sm3+ ions

and the energy transfer probability in (Sm3+:V4+) co doped NSZ glasses is

monitored, investigating the structural changes that takes place due to

oxidation state of vanadium. The shifting role of modifier ions varied in the

spectroscopic and optical properties of Sm2O3 ions in Na2O-SiO2-ZrO2

glasses co doped with V2O5 using XRD, EDS, EPR, FT-IR, Raman spectra,

Optical Absorption and Luminescence studies are recorded.

~ 211 ~

Analytical reagents with 99.9% purity of Na2CO3, SiO2, ZrO2,

Sm2O3 and V2O5 are used to prepare the glasses. Here samarium and

vanadium are employed as dopants in the glasses network. Glasses were

prepared by using melt quenching technique; in this calculated quantities of

chemicals in mol% were taken in an agate mortar and then powdered to

obtain homogeneous mixture. The mixture is taken in silica crucible and

heated for about 1 hour in an automatic temperature controlled furnace at a

temperature range 1350-1450oC. The melt is quickly poured in to preheated

brass mould so as to obtain the required shape. The obtained samples were

immediately transferred to the muffle furnace of 450oC temperature for

annealing. The muffle furnace containing samples was switched off

immediately and left to cool at room temperature at a rate of 25oC/h to

avoid thermal stress and to get the structural stability. Later the samples

were polished to final dimensions of 1cm x 1cm x 0.2 cm. The glass

samples are transparent and appear to have good optical quality. The

composition of the prepared glasses containing variable amount of contents

are given in Table 1.

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Table 1: Composition of the studied glasses (batch mol %)

S.No. Glass Na2O (mol %)

SiO2 (mol %)

ZrO2 (mol %)

Sm2O3 (mol %)

V2O5 (mol %)

1 pure 40 55 5 - -

2 Smv0 40 54 5 1 -

3 Smv1 40 54 4.8 1 0.2

4 Smv2 40 54 4.6 1 0.4

5 Smv3 40 54 4.4 1 0.6

6 Smv4 40 54 4.2 1 0.8

7 Smv5 40 54 4 1 1.0

Density of the glasses was determined to an accuracy of (0.0001)

by the standard Archimedes Principle using o-xylene (99.9% pure) as

buoyant liquid and the refractive index of the glass sample is measured by

using Abbe’s refractrometer. The X-ray diffraction spectrum is recorded on

a diffractometer with copper target (XRDARLX’TRA) and nickel filter

operated at 40KV, 30mA. The Energy Dispersive Spectroscopy

measurements were conducted on a Thermo Instruments Model Noran

System 6 attached to scanning electron microscope. The electron spin

resonance (ESR) spectra of the fine powder of the sample were recorded at

room temperature. Infrared Transmission Spectra are recorded on a

JASCO-FT-IR -53000 spectrophotometer with resolution of 0.1cm-1 in the

spectral range 400-4000cm-1 using KBr pellets (300mg) containing the

pulverized sample (1.5mg). The Raman Spectra (model Nexus 670 Nicolet

– Madison –W.I.USA) is recorded on Fourier transform Raman

~ 213 ~

spectrometer with resolution of 4 cm-1 in the 400-1500cm-1.The optical

absorption (UV-Vis) Spectra are recorded on JASCO, V-570

Spectrophotometer from 200 to 1800 nm with Spectral resolution of 0.1nm.

The luminescence Spectra are recorded at room temperature on a photon

Technology International (PTI) spectroflurometer with excited wavelength

400 nm from 300-1200nm.

4.2 Brief review of previous work on Samarium doped glasses

A. Edgar et al [30] report the 4f → 4f transitions for Sm2+ ions in the

orthorhombic phase of barium chloride show an abrupt change in the

relative intensity of transitions originating from the 5D1 and 5D0 levels at

around 90 K. The effect is attributed to the role of the 5d level in thermally

assisted indirect transitions between the 5D1 and 5D0 levels. In contrast,

transitions from only the 5D0 level are observed for the hexagonal phase.

Pedro Damas et al [31] reports the preparation and structural studies of

praseodymium and samarium (0.5, 2 and 4 mol %) oxide doped lithium

boro tellurite glasses. These materials were prepared by the quenching

technique in a ceramic crucible at 950 °C. Structural characterization was

performed. M. Reza Dousti et al [32] investigated P2O5-PbO-ZnO-Sm2O3

glasses; absorption spectra consist of seven absorption peaks corresponding

to the transitions from the 6H5/2 ground state to various excited energy

levels. Photoluminescence spectra show four prominent emission bands

~ 214 ~

centered at 560, 597, 642 and 700 nm corresponding to the 4G5/2−6HJ

(J=5/2, 7/2, 9/2, and 11/2) transitions respectively and the intensities of all

bands are enhanced by Sm3+ ions content.

B. Eraiah et al [33] studied Samarium doped zinc–phosphate glasses,

No sharp edges were found in the optical spectra, which verifies the

amorphous nature of these glasses. The optical band gap energies for these

glasses were found to be in the range of 2.89–4.20 eV. The refractive index

and polarizability of oxide ion have been calculated by using Lorentz–

Lorentz relations. M. Elisa et al [34] studied on Li2O–BaO–Al2O3–La2O3–

P2O5 system containing Sm3 + and Eu3 + ions, the influence of Sm3 + and

Eu3 + ions on the optical properties of these glasses has been investigated in

relation with their structural characteristics. The optical behavior of these

materials has been studied by ultra-violet–visible (UV–Vis) spectroscopy,

revealing absorption maxima specific to the doping ions. S.A. Reduan et al

[35] investigated Li2O-MgO-B2O3 doped with Sm2O3, the absorption

spectra of this study showed four absorption bands with most outstanding

peak at 1230 nm (6H5/2–6F7/2). Three emitted spectra transition were

observed in this study which are 4G5/2–6H5/2 (blue), 4G5/2–

6H9/2 (green), and

4G5/2–6H11/2(yellowish green).

Maria Czaja et al [36] investigated praseodymium and samarium

ions in phosphate glass, the results obtained for the J–O theory application

to phosphate glasses doped with Pr3+ and Sm3+ present two undesirable

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outcomes: (1) a positive value of parameter Ω2 and (2) large uncertainties

with which the three Judd–Ofelt parameters were obtained. The validity of

the J–O theory for intensity analysis was also tested for Sm3+ doped in

phosphate glass. The resulting Ω2 was much lower than Ω4. Parvinder Kaur

et al [37] studied on Cerium and samarium codoped lithium aluminium

borate glasses, the UV–Vis absorption spectra shows an increase in

intensity and a significant shift of the optical absorption edge from UV to

partially visible region when cerium is added in the pure samarium

containing lithium aluminium borate glass. The fluorescence spectra

indicate an energy transfer from Ce3+ to Sm3+ ions. K. Swapna et al [38]

investigated Zinc Alumino Bismuth Borate glasses doped with Sm3+ ions,

The emission spectra of Sm3+ ions doped ZnAlBiB glasses show two

intense emission bands 4G5/2→6H7/2 (orange) and 4G5/2→

6H9/2 (red) for

which the stimulated emission cross-section and branching ratios are

evaluated to understand the potentiality of these materials as visible lasers.

Parvinder Kaur et al [39] investigated on Samarium doped lithium

aluminium borate glasses, The UV–vis–NIR absorption spectra show an

increase in intensity of different transitions from the ground level 6H5/2 to

various 2S+1LJ levels with an increase in samarium concentration at the

expense of aluminium. The fluorescence spectra show several transitions

from 4G5/2 to various 6HJ levels along with 4F3/2 to 6HJ and 4G7/2 to 6H5/2.

~ 216 ~

Y. Dwivedi et al [40] studied on Sm: Ce doped in barium

fluoroborate glasses, Luminescence spectrum of Sm: Ce codoped glass

sample reveals strong energy transfer from Ce3+ to Sm3+ ions. In Sm:Ce

doped sample, emission intensities of Sm3+ as well as of Ce3+ bands are

reduced considerably with 355 nm excitations, while intensities of Sm3+

bands are enhanced under 266 nm excitations. The reduction in emission

intensity on 355 nm excitations is verified with the formation of Ce4+ and

Sm2+ ions while in case of 266 nm excitation, energy transfer from Ce4+–O

charge transfer state to Sm3+ ion is expected to dominate. O. Ravi et al [41]

studied samarium doped TeO2-RO-ZnO-Nb2O5-B2O3 glasses, The FT-IR

spectra and FT-Raman studies reveal the presence of [BO3], [BO4] and

[TeO3], [TeO4] bridging and non-bridging oxygen as well as strong OH

bonds in the prepared glasses. The experimental oscillator strengths were

determined from the absorption spectra and have been used to determine J–

O intensity parameters Ωλ (λ = 2, 4 and 6). Sd. Zulfiqar Ali Ahamed et al

[42] reported on Sm3+ doped PbO-BaO-ZnO-LiF-B2O3 glasses, the values

of J–O intensity parameters suggested an increase in the degree of

symmetry of the local ligand field at Sm3+ sites. The decay rates for the

4G5/2 level of Sm3+ ions have been measured and are found to be single

exponential at lower concentrations (<1.0 mol%) and turn into non-

exponential at higher concentrations (⩾1.0 mol%), due to energy transfer

through cross-relaxation. Peijing Tian et al [43] studied Sm3+ doped CaO-

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MgO-Al2O3-SiO2 glasses According to the fitting results, we demonstrate

that the Sm2O3 exist in glass network as a glass modifier. After heat

treatment, nearly all the Sm3+ existed in diopside phase as the substitution

for Ca2+.

Y.N.Ch. Ravi Babu et al [44] reported on lead bismuth magnesium

borophosphate glass doped with Samarium, The Judd–Ofelt

parameterization employed reflects the covalency and vibration frequencies

of the ligands with Samarium ions. The glass systems thus developed

indicate their potential lasing candidature. The emission cross sections (σE)

for the significant lasing transitions 4G5/2→6H5/2,

4G5/2→6H7/2, and

4G5/2→6H9/2 evaluated from the photoluminescence spectra were reported.

Fakhra Nawaz et al [45] reported on Sm3+/Yb3+ co-doped sodium tellurite

glasses, The UV–vis–NIR spectra exhibit eight absorption bands

corresponding to the transition from ground level 6H5/2 to the various

excited state of Sm3+ ions and the broad absorption band in the range of

~825–1100 nm is ascribed to the large contribution of the absorption from

2F7/2→2F5/2 transition of Yb3+ ion. The experimental oscillator strengths

calculated from the absorption spectra are used to evaluate three

phenomenological Judd–Ofelt (J–O) intensity parameters Ωλ (λ=2, 4 and 6).

Emission spectra consist of four bands 4G5/2→6H7/2 (moderate green)

4G5/2→6H5/2 (intense orange), 4G5/2→

6H7/2 (moderate orange-yellow) and

4G5/2→6H11/2 (feeble red). Abu Zayed Mohammad Saliqur Rahman et al [46]

~ 218 ~

reported luminescence study of Sm-doped SiO2–Na2SO4 composite,

photoluminescence (PL) spectra of as-synthesized composite phosphors

obtained under 402 nm excitation consist of five narrow emission bands

with peaks at 563, 598, 644, 704 and 784 nm, respectively. These are

assigned to the 4G5/2→6HJ (J=5/2, 7/2, 9/2, 11/2 and 13/2, respectively)

transitions within 4f5 electronic configuration of Sm3+. M.A.K. El-Fayoumi

et al [47] reported Li–borate glasses doped with Sm3+ and Eu3+ ions, the

results showed that the three main appeared bands are most likely due to

the bending and/or stretching vibration of both tetrahedral BO4 and

triagonal BO3 borate units.

S. Shanmuga Sundari et al [48] reported Sodium borate and

fluoroborate glasses doped with samarium, the dependence of the spectral

characteristics of Sm3+ ions due to compositional changes have been

examined and reported. The value is found to decrease with the decrease in

the sodium content in the glass. The decay from the 4G5/2 level is found to

be non-exponential indicating a cross-relaxation among the Sm3+ ions.

Yasser Saleh Mustafa Alajerami et al [49] reported lithium magnesium borate

glasses doped with Dy3+ then with Sm3+ ions, the Sm3+, nine absorption

bands were observed with hypersensitive transition at 1237 nm (6H5/2–

6F7/2); the PL spectrum showed four prominent peaks at 4G5/2→6H5/2

(yellow color), 4G5/2→6H7/2 (bright orange color), 4G5/2→

6H9/2 (orange

reddish color) and 4G5/2→6H11/2 (red color), respectively.

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4.3 Results

4.3.1 Physical Properties

To understand the physical properties of the glasses, various

parameters are calculated, i.e. practically measured density (d) and

refractive index (The error in density measurements and refractive indices

are estimated to be ± 0.004 g/cm3 and ± 0.0001 respectively) are calculated.

Along with this function, some other physical parameters also calculated

[50-53] using conventional formulae such as vanadium ion concentration

(Ni), mean ionic separation (ri), polaron radius (rp), field strength (Fi),

electronic polaraizability (α), reflection loss, Molar refractivity(RM) and

optical dielectric constant (ε) which are presented in the Table 2. The

variation of density and refractive index with glass sample is shown in the

Fig 1. And also the change in the ionic concentration and electronic

polarization with glass sample is shown in Fig 2.

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Table.2: various physical properties of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

Figure.1: Variation of density and refractive index with glass sample of

Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

Physical Parameters pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5

Density d (g/cm3) (±0.004) 2.679 2.692 2.718 2.780 2.785 2.769 2.762

Average molecular weight (M) 63.99 66.88 67.00 66.71 66.63 66.55 66.46

Ion concentration

Ni(1020ions/cm3)(±0.005) - - 0.488 1.004 1.510 2.005 2.502

Interionic distance ri

(Å)(±0.005) - - 27.35 21.51 18.77 17.08 15.86

Polaron radius rp(Å) (±0.005) - - 11.02 8.66 7.56 6.88 6.39

Field strength F i(1015cm-2)

(±0.005) - - 2.47 3.99 5.24 6.33 7.33

Refractive index n (±0.0001) 1.674 1.662 1.663 1.665 1.667 1.666 1.667

Reflection loss 0.033 0.032 0.032 0.032 0.033 0.033 0.033

Molar reflectivity RM(cm-3)

(±0.005) 8.969 9.197 9.131 8.909 8.904 8.940 8.957

Electronic polarizability (αe)

(10-22 ions/cm3)(±0.005) - - 18.106 8.832 5.885 4.431 3.552

Optical dielectric constant(ε0)

(±0.005) 2.803 2.763 2.765 2.772 2.778 2.777 2.778

~ 221 ~

Figure.2: Variation of ionic concentration and electronic polarizability of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

4.3.2 X-ray diffraction spectra

The amorphous nature of the Sm3+:V4+ co-doped NSZ glasses was

confirmed by X-ray diffraction spectra, which Shows a broad bump around

the centered 27o (=2). There are no observed sharp lines which shows that

all the prepared samples confirms the amorphous nature and it is shown in

Fig 3.

Figure.3: XRD spectra of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

~ 222 ~

4.3.3 Energy Dispersive Spectroscopy

From the Energy Dispersive Spectroscopy (EDS), the chemical

compositions of the glasses were determined as shown in Fig 4. The inset

figure shows the electronic image spectrum of the glass sample of 1mol%

V2O5. The analysis indicates the presence of sodium (Na), silicon (Si),

zirconium (Zr), samarium(Sm), oxygen (O), carbon(c), and vanadium (V)

elements in the glass network.

Figure.4: EDS spectra of 1 mol% V2O5 in Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

4.3.4 Fourier transforms Infrared transmission spectra (FT-IR)

The Fourier transforms Infrared transmission spectra gives

information about the various vibrational modes and also provides

structural information of the glass network. The spectra of undoped and

doped Sm3+:V4+ codoped NSZ glasses are shown in Fig 5. The spectral

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features are analyzed from the studied glasses show the vibration bands

without any obvious variations. The observed IR spectral bands are given

in Table 3. The spectra exhibit a series of bands [54] one at about 470cm-1 ,

the second band at around 640-660cm-1 and the third at around 730-760cm-

1. Two bands are located at around 800-900cm-1 and one sharp band with a

peak is located at about960-970cm-1. Another belonging to the OH groups

is found around 1500-1700cm-1 [55].

Table.3: The FT-IR band positions of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

GLASS SAMPLES Band assignments

pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5

470 471 470 470 471 470 471 Bending and rocking

motion of Si-O-Si

- - 648 653 653 652 653 V-O-V bending

vibrations

732 742 743 743 742 743 743 Zr-O-Zr/ZrO4

structural units

- - 836 818 816 816 818 V-O-V chains

890 884 884 883 884 888 889 Si-O-Si symmetric

stretching vibrations

961 968 964 963 965 963 965 Si-O-Zr units

1517 1522 1527 1522 1522 1524 1524 Stretching mode of Si-

OH

1695 1695 1696 1695 1695 1696 1696 Water molecular

vibrations

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Figure.5: FT-IR spectra of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

4.3.5. Raman spectra

Raman spectra are used to characterize the local arrangement of the

structure of the glasses and also give information about the structural

properties that would support the Infrared transmission spectra. Fig 6

represents the Raman spectra of the undoped and doped Sm3+:V2O5 NSZ

glasses. The Raman spectra of the glasses and band positions are presented

~ 225 ~

in Table 4. The spectra of NSZ glasses have revealed a peak at round 350-

365cm-1 and structural vibrations are observed at around 800 cm-1. In the

spectrum contains V2O5, stretching vibrations are observed at around

600cm-1 and another two band is observed at 900cm-1 and 1070cm-1 [56-

58].

Figure.6: Raman spectra of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

~ 226 ~

Table.4: Raman band positions of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

4.3.6 Electron paramagnetic resonance spectra

Electron paramagnetic resonance spectra is a method to understand

the symmetry of surroundings of the paramagnetic ion and the nature of its

bonding with the nearest neighboring ligands. The EPR spectra recorded at

room temperature for the present investigated NSZ: Sm3+:V4+ co-doped

glasses. No signals are observed for the undoped glasses. When V2O5 are

introduced into the glass matrix, the EPR resonance spectra exhibit eight

parallel and eight perpendicular lines arising from the unpaired 3d1 electron

of VO2+ ions with 51V(I=7/2) isotope in an axially symmetric field. The

GLASS SAMPLES Band assignments

pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5

353 353 355 357 361 361 361 Si-O-Si rocking

vibrations

- - 617 617 615 612 612 V-O-V vibrations/combinations of various vibrations

856 854 854 852 853 856 856 Si-O-Si bending

vibrations

949 947 947 949 949 947 947 Si-O-Zr rocking

vibrations

1090 1091 1091 1092 1091 1092 1091 Si-O-Si stretching

vibrations

~ 227 ~

axial spin-Hamiltonian for hyperfine interaction is used to describe the

spectra of V4+ ions [59].

H= β [gǁBzSz+g (BxSx+BySy)] +AǁSzIz+A (SxIx+SyIy) ---------- (4)

Here β denotes Bohr magneton, gǁ,g and Aǁ,A denotes the

components of the hyperfine coupling tensor, Bx, ,By and Bz denotes

components of the magnetic field, Sx, Sy, Sz and Ix, Iy, Iz are the spin

operator of the electron and the nucleus . The magnetic field positions for

the parallel and perpendicular hyperfine peaks are based on the second

order perturbation terms are

2

263( ) (0)

1 (0) 4

Am mA m

B

---------- (5)

22

263

( ) (0)4 (0) 4

A Am mA m

B

---------- (6)

From the above equation m refer to the nuclear spin magnetic quantum

number, bearing values 7/2, 5/2, 1/2; Bǁ (0) =h/gǁβ and B (0) =h/gβ.

From the above parameters, the dipolar hyperfine coupling parameters

P=2ββN 3

r

and the Fermi contact interaction (K), are evaluated [60]

using the expression

Aǁ=P [(-4/7)-K+ (gǁ- ge) + (3/7) (g-ge)] ----------- (7)

A=P [(2/7)-K+ (11/14) (g-ge)] ----------- (8)

~ 228 ~

In the equation, ge=2.0023 and refer to the g factor of the free electron. The

term P and K in the above equation result from the S-character of the

magnetic spin of the vanadium. Generally the s-character is due to the

partial unpairing or polarization of the inner s-electron gives the interaction

with the unpaired d electrons. The values gǁ / g are also calculated for

the tetragonality of the vanadium site. The molecular bonding coefficient

β*2 and επ*2 are evaluated by correlating the EPR and optical data using [61]

the given expressions

β*2= ( )

8eg g

---------- (9)

επ*2=

( )

8eg g

---------- (10)

In the above equation, λ is the free-ion value of spin orbit coupling

constants for the vo2+ ions and is taken as 170cm-1. ǁ and are energies

of the electronic transitions from 2B22Bg and 2B2

2Eg respectively. The

above evaluated values from these spectra along with the other pertinent

data are furnished in Table 5.

~ 229 ~

Table.5: The spin-Hamiltonian parameters and molecular orbitals coefficients for Na2O-SiO2-ZrO2: Sm3+:V4+ codoped

glasses

Glass

code gǁǁ g

Aǁǁx10-4

cm-1

A x10-4

cm-1 β*2 επ

*2 gǁǁ g gǁǁ/g Px10-4

cm-1 K

AǁǁI x10-4

cm-1

AI x10-4

cm-1

Smv0 1.8926 1.9085 183 67 0.0471 0.0863 0.0938 0.1097 0.8550 -144.5 0.8355 62.28 53

Smv1 1.8967 1.9191 181 66 0.0417 0.0830 0.0832 0.1056 0.7878 -140.4 0.8476 62 53

Smv2 1.8967 1.9191 181 66 0.0417 0.0830 0.0832 0.1056 0.7878 -140.4 0.8476 62 53

Smv3 1.8968 1.9191 181 66 0.0417 0.0830 0.0832 0.1055 0.7886 -140.2 0.8478 62.2 52.8

Smv4 1.8966 1.9186 181 66 0.0420 0.0831 0.0837 0.1057 0.7918 -140.2 0.8479 62.2 52.8

~ 230 ~

4.3.7 Optical absorption spectra

The absorption spectra of Sm3+: V4+ ions codoped NSZ glasses show

a large number of bands; the observed bands are assigned on the basis of

the reported energy levels [62-65] of Sm3+ ions of different glass hosts.

With the addition of V2O5, the absorption intensity enhances and exhibit

more absorption band. The bands are observed at 402,470 1070, 1221,

1260, 1360, 1370, 1465, 1522nm [66-67] these bands are related to

samarium (Sm3+) ions resulting due to the different transitions are from

6H5/2 6P3/2,4I13/2+

4I11/2+4M15/2,

6F9/2, 6F7/2,

6F5/2,6F3/2,

6F1/2,6H15/2. When V2O5

is added to the glass network two more additional bands are observed at

683 and 1070nm due to the transitions 2B22Bg and 2B2

2Eg. Thus, from

these optical absorption spectra totally nine bands are observed for

Sm3+:V4+ doped NSZ glasses as shows in Fig 7. From the observed edge,

we have evaluated the optical band gap (Eo) of these glasses by drawing

Tauc plot between (αhν) 1/2, (αhν) 2 as a function of hν as per the given

equation

α (ν) hν=C (hν- Eo)n ---------- (1)

Here C is a constant and the exponent (n) can take values 1/2 and 2

for indirect, direct transitions in glasses respectively [68]. Tauc plots for

direct transition in Fig 8(a) and indirect transition are shown in Fig 8(b).

Extrapolating the linear portion of these plots as (αhν)1/2 = 0, (αhν) 2 =0

gives optical band gap, along with the theatrical optical band gap energy

~ 231 ~

also calculated using equation E=hc / λ. Here h is the plank’s constant, c is

the velocity of light and λ cutoff wavelength respectively. The value of E

is calculates by taking the reciprocal of the slope of the linear portion in the

lower photon energy region of ln (α) verses hν plot are shown in Fig 9.

Urbach energy which corresponds to the width of localized states and

characterizes the degree of disorder in the glass systems. The value of E

in the present work lies in the range 0.25 – 0.27 eV for all the glasses. The

increase in Urbach energy with increasing the concentration of V2O5. In

addition to this, the theoretical optical basicity (th) of the glasses can be

calculated for the Sm3+ :V2O5 doped NSZ glasses [69-70] by using the

formula

1

ni i

th

i i

Z r

Z

---------- (2)

Where n denotes the total number of cations present, Zi denotes the

oxidation number of the ith cation, ri denotes the ratio of the number of the

ith cation to the number of oxides present and i denote basicity moderating

parameters of ith cation. The basicity moderating parameter is calculated

from the following equation

i=1.36(xi-0.26) ---------- (3)

Where xi represents the pouling electro negativity of the cation. The

theoretical and evaluated values of cutoff wavelength, theoretical band gap,

~ 232 ~

direct and indirect band gap and the theoretical optical basicity (th) are

presented in Table 6.

Table.6: The cutoff wavelength, optical band gaps, Urbach energy and optical Basicity of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

Figure.7: Optical absorption spectra of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

GLASS

SAMPLES

Cutoff

wavelength

Theoretical

band gap

Direct

band

gap(eV)

Indirect

band

gap(eV)

Urbach

energy

(E)(eV)

th

pure 315 3.94 3.92 3.91 0.2544 0.110

Smv0 323 3.86 3.84 3.85 0.2604 0.088

Smv1 328 3.78 3.77 3.75 0.2666 0.088

Smv2 338 3.67 3.65 3.65 0.2754 0.088

Smv3 341 3.64 3.62 3.61 0.2770 0.087

Smv4 343 3.62 3.61 3.59 0.2785 0.087

Smv5 345 3.60 3.59 3.58 0.2793 0.088

~ 233 ~

Figure.8: Tauc plots to evaluate (a) direct band gap, (b) in-direct band gap of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

(a)

(b)

~ 234 ~

Figure.9: A plots of ln (α) and hν for Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

4.3.8. Photoluminescence spectra

The Photoluminescence spectra of Sm3+: V4+ doped NSZ glasses are

recorded at room temperature with excited wavelength 400 nm in region

450-900 nm. When Sm3+ ions are excited at 6P3/2 level (402 nm), the initial

population relaxes finally to the 4G5/2 level. Between 6P3/2 and 4G5/2 levels,

there are several intermediate levels with smaller energy difference, which

encourage their efficient non-radiative relaxation there by leading to the

population at the 4G5/2 state. This state is distinct from the intermediate

lower state i.e. 6F11/2. It could be stated that radiative transitions and

relaxations by non-radiative energy transfer are the two main processes,

~ 235 ~

which could finally depopulate the 4G5/2 state. The emission spectra of the

NSZ glasses containing Sm3+ ions exhibit four emission transitions, which

are assigned to 4G5/26F5/2 (576 nm), 4G5/2

6F7/2 (604 nm), 4G5/26F9/2

(648 nm) and 4G5/26F11/2 (708 nm) [71-72]. By the addition of V2O5

another band is observed at round 782nm with the transition 2E2T2 [73-

74]. The Fig 10 shows the luminescence spectra of Sm3+:V4+ codoped NSZ

glasses.

Figure.10: Luminescence spectra of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

~ 236 ~

4.4 Discussions

Among the physical properties, density is an effective tool to

explore the degree of structural compactness of the glasses. In the present

work, increase in density is observed with the increasing content of V2O5 in

all the glasses. Basically, when V2O5 enters into the glass network in two

forms, they acts as network modifier at low content and at high content it

acts as network forming group. Due to this, non bridging oxygen content is

further increases. The density and refractive index of the observed

parameters vary non- linearly with increasing vanadium concentration.

From these observations, the effect of V2O5 in ionic concentration and

electronic polaraizability of Sm3+:V2O5 NSZ glasses vary non-linearly. It is

observed that both the parameters tend to be inversely proportional to the

increase in x mol% of vanadium concentration. The polaraizability is high

at x=1 mol%, whereas, its ionic concentration lower due to feeble ionic

mobility and increase in interionic separation (ri) is observed. An eventual

decrease in interionic separation is noticed when content of V2O5 increases

in the glass network.

The infrared transmission spectra of Na2O-SiO2-ZrO2 codoped

Sm3+:V4+ glasses contain different structural units. Within the glass region,

rare-earth ion Sm2O3 content is present, due to this there is no significant

difference is observed, but may be shifted to lower frequency. The glass

system consists of Na2O causes some of the oxygen atoms and bounded by

~ 237 ~

silicon atoms and termed as bridging oxygen. Due to this, Si-O-Si rocking

bands are observed at 470cm-1 in the glass system [75]. The percentage of

non bridging oxygen increases with an increases vanadium in content in the

glass network V-O-V bending vibrations are present at around 640-660cm-1

[76]. Due to the presence of intermediate oxides ZrO2, Zr-O-Zr / ZrO4

structural units are present in the glass network at 730-760cm-1 [77]. Due to

the increase in non bridging ions some bonds are replaced and Si-O-Si

symmetric stretching vibrations are observed at 800-900cm-1. The band

observed at around 960-970cm-1 is obtained due to the presence of Si-O-Zr

structural units [78]. The deformed vibrations or stretching bands are

observed at around 1500-1700cm-1 exists due to form of OH groups in NSZ

glasses.

The NSZ codoped glasses are characterized by the Raman spectra.

In these Raman spectra we can observe the similar patterns with the

presences of Sm3+ ions in the glass matrix as the bands are shifted towards

lower frequency. The spectra of all the glasses are correlated with the IR

spectra that the Raman spectra of glasses indicates the vibrational bands at

around 350-365cm-1 is due to the Si-O-Si asymmetric vibrations [79]. With

the addition of V2O5 in the composition range 0.2 to 1.0 mol%, the V-O-V

vibrational band and combination of another band are observed around

600cm-1 [80-81]. The band around 800cm-1 causes Si-O-Si symmetric

stretching vibrations and at around 900cm-1. The band is observed due to

~ 238 ~

the Si-O-Zr vibrational units [82] or stretching vibrations of vanadium and

at around 1070cm-1 there is a Si-O-Si vibrations are observed in the Raman

Spectra of codoped Sm3+:V4+: Na2O-SiO2-ZrO2: glasses.

Fig 11 shows the EPR spectra of Na2O-SiO2-ZrO2: Sm3+:V4+

glasses. From this EPR spectra the increased intensity of the signals are

observed with an increased the concentration of V2O5, usually vanadium

ions seems to exist mainly in V4+ and V5+ state . During the preparation of

glasses at high temperature there is a possibility for the following redox

equilibrium is takes place 2V5++O2-2V4++ 1/2O2. In this region, the

presence of the larger concentration of V4+ ions may also be due to

exchange coupling between V3+ ions (if any) and V4+ ions. The spectra of

V4+ ions are found to exist in either threefold symmetry or fourfold

symmetry. This describe the crystal field of V4+ ions in glasses and the V4+

ions in the NSZ glasses existing in octahedral coordination with a

tetragonal compression and having C4v symmetry. An octahedral site with a

tetragonal compression gives the value of gǁ>g>ge [83-88].

~ 239 ~

Figure.11: EPR spectra of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

From these observations, it is suggested that the paramagnetic V4+

ion in the glass of vanadyl ion VO2+ is in an octahedral environment with

tetragonal distortion. The acquire hyperfine values of the present study

suggests a lesser distortion within the glass matrix. This quantitative

analysis of EPR result indicates that the ratio of gǁ / g is observed to

decrease gradually with ion concentration of V2O5 indicating an increasing

degree of distortion of the VO6 octahedron. The molecular orbital

~ 240 ~

coefficient values indicate that the degree of covalence in V-O- bonds

(β*2) and π-bonding with the vanadyl oxygen (επ* 2) of all glasses has

covalence [89-91]. This EPR study indicates that the tetragonal distortions

decrease with increasing V2O5 concentration in the NSZ codoped Sm3+:V4+

glasses.

The absorption spectrum of Na2O-SiO2-ZrO2: Sm3+:V4+ glasses, the

transition in the absorption spectrum of Sm3+ ions starts from the ground

state 6H5/2 raising to the various excited states. The transitions observed in

the absorption spectrum with (f-f) transition are almost overlapping with the

surrounding ions. The spectrum consists of V4+ an ion belongs to d1

configuration. Vanadyl ion exhibited the three absorption bands on the

basis of energy level scheme of VO2+ ions in a ligand field C4v symmetry.

The transitions are 2B22Bg,

2B22Eg and 2B2

2A1, for the present glasses

exhibit only first two transitions are observed. The largest intensity of the

half width of these bands is observed that indicating the presence of the

concentration of VO2+ ions in these glasses. The optical band gap for direct

and indirect transitions of the sample is found to decrease with an

increasing the concentration of dopant V2O5 in the glass matrix due to

increase of non-bridging oxygen ions. The observed theoretical optical

basicity is found to decrease with an increasing concentration of dopant

indicating an increase in covalent nature of the glasses. The Judd-Ofelt (JO)

theory has been used to compute the radiative and nonradiative properties

~ 241 ~

of the excited states in the Ln3+-doped complexes. Among the JO

parameters, 2 is associated to the covalency of the Ln–O bond as well as

asymmetry around the Ln3+ ion site, while 4 and 6 parameters are long

range parameters that can be related to the bulk properties of the glass such

as viscosity and basicitiy of the matrix and 6 to the 6s electron density of

Ln3+ ions [92-94]. The degree of covalency of Ln–O bond can be

determined by shifting hypersensitive absorption bands to higher

wavelengths due to nephelauxetic effect. Lower the symmetry in the

vicinity of the Ln3+ ion higher will be the value of 2 parameter. It is well

known that 2 is strongly enhanced by covalent bonding, which is

equivalent to the dynamic polarization of the ligands by the quadrupole

moment of the transitions. Ω6 is affected more than that of Ω2 and Ω4 due to

change of the overlap integrals of the 4f and 5d orbitals [93]. Conventional

Judd-Ofelt (J-O theory) parameter has been calculated from the absorption

spectra of Sm3+ ions. The absorption spectra of rare earth ions are useful to

understand the radiative properties. The absorption line arising from 4f

4f electronic transition can reflect an electric dipole, a magnetic dipole or

an electric quadrapole characteristic. The electric dipole transitions between

two states within 4f configuration are forbidden, while magnetic dipole and

electric quadrapole transitions are allowed. The intensity of the absorption

bands can be estimated by using oscillator strength fexp, which is calculated

from the absorption spectra by using following equation

~ 242 ~

fexp= 4.318x10-9( )dv dν ---------- (11)

Where ε (ν) denotes the molar extinction coefficient at average

energy ν in cm-1. According to the f-f intensity model of the J-O theory,

[95] the calculated oscillator strength from initial state to an excited state

are described by the expression

f (ψJ; ψ′J′) =8 2 ( 2 2)2

3 (2 1) 9

mcv n

h J n

X 2,4,6

(ψJǁUλǁψ′J′) 2 ------- (12)

where m refer to the mass of the electron, c is the velocity of light in

vacuum, h is the plank’s constant, n is the refractive index of refraction of

the glass, ν is the frequency of the transition ψJψ′J′, Ωλ (λ=2, 4 and 6) are

the J-O intensity parameters and ǁUλǁ are the doubly reduced matrix

elements of the unit tensor operator of the rank λ=2, 4 and 6 which are

evaluated from the intermediate coupling approximation for a transition

ψJψ′J′. The experimental oscillator strengths of absorption bands of Sm3+

doped glass are determined from the known values of Sm3+ concentration,

sample thickness, peak position and peak areas by using the equation 11.

The rare earth ions that occupy different coordination sites with non-centro

symmetric potential contribute significantly to Ω2. Even with similar

coordination, the differences in the distortion at these ion sites may lead to

a distribution in the crystal field. Variations in the sites with non-centro

symmetric potential (that may arise due to the influences of the dielectric of

media, the environment of the rare earth ion and nephelauxetic effect) lead

~ 243 ~

to changes in Ω2 value. By applying least square fitting procedure to

determine the J-O intensity parameters Ω2, Ω4 and Ω6 using experimentally

measured oscillator strength, the obtained values are presented in Table 7.

The J-O intensity parameters determined in the present glass network are

found to be in the order Ω2> Ω4> Ω6. As shown in Table 8. The rare earth

ions that occupy different coordination site with non-centro symmetric

potential contribute significantly to Ω2 [96-98]. The parameter Ω2 is related

to the covalence and structural changes of the Sm3+ ion and Ω4 and Ω6 are

related to the long-range effect. They are strongly influenced by the

vibration levels associated with the central rare earth ions bound to the

ligand atoms.

~ 244 ~

Table 7: Theoretical and experimental oscillator strength of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

Transition

6H5/2→

Smv0 Smv1 Smv2 Smv3 Smv4 Smv5

fcal,(x10-6) fexp,(x10-6) fcal,(x10-6) fexp,(x10-6) fcal,(x10-6) fexp,(x10-6) fcal,(x10-6) fexp,(x10-6) fcal,(x10-6) fexp,(x10-6) fcal,(x10-6) fexp,(x10-6)

6F9/2 2.0276 2.12798 2.22356 2.2374 2.2178 2.0276 2.0163 2.0676 2.0154 2.0168 2.0726 2.1876

6F7/2 3.2298 3.29876 3.3239 3.3289 3.2654 3.2896 3.1292 3.1598 3.1146 3.1393 3.2532 3.2923

6F5/2 2.2309 2.33568 2.4309 2.3219 2.2439 2.2367 2.219 2.2249 2.2567 2.2309 2.2093 2.2039

6F3/2 1.3654 1.4654 1.5683 1.5967 1.3748 1.3657 1.3098 1.3262 1.3983 1.3679 1.3768 1.3567

6F1/2 0.6120 0.62965 0.6820 0.6902 0.6290 0.6548 0.6018 0.6125 0.6062 0.6164 0.6156 0.6198

6H15/2 0.4441 0.4964 0.6534 0.6487 0.556 0.5846 0.4398 0.4367 0.4561 0.4679 0.4344 0.4545

Rms

deviation

0.0805

0.0465

0.0800

0.0258

0.0202

0.0510

~ 245 ~

Table 8: J-O intensity parameters of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

The Photoluminescence spectra of the codoped Sm3+:V4+ NSZ glass

system exhibit four emission transitions due to Sm3+ ions in which

transition 4G5/26H7/2 (604 nm) has a strong orange red emission. The

transition 4G5/26H7/2 with J=1 is not only a magnetic dipole (MD)

allowed one, but it is also an electric dipole(ED) dominate [99-100], the

other transition 4G5/26H9/2 is purely an electric dipole. Hence, the

intensity ratio of electric dipole to magnetic dipole transition has been used

to measure the symmetry of the local environment of the trivalent 4f ions.

In this 4G5/26H9/2 transition of Sm3+ ion is more intense than 6H5/2

conforming the asymmetric nature of the glass host. In the present glass

system the concentration of sm3+ was fixed at 1 mol%. We observed an

increase in vanadium; the energy transfer takes place from vanadium to

samarium. However, it will decrease due to the concentration quenching

GLASS

SAMPLES

Ω2x10-20 (cm-

2)

Ω4 x10-20

(cm-2)

Ω6 x10-20

(cm-2)

Smv0 3.65 3.31 2.42

Smv1 3.81 3.52 2.46

Smv2 3.72 3.47 2.43

Smv3 3.68 3.43 2.38

Smv4 3.63 3.39 2.34

Smv5 3.59 3.35 2.31

~ 246 ~

between the ions [101]. The energy transfer mechanism between Sm3+:V4+

codoped NSZ glasses with variation in concentration are found cause

dipole-dipole interaction. The small energy separation between the two

levels of Sm3+ to V4+ indicates that they are thermally coupled to each other

and the population ion at the two levels with a fixed concentration will

depend on the temperature of the glass. This dependence of temperature is

due to energy transfer or by multiphonon relaxation. Fig 12 represents the

energy level scheme for all the observed absorption, excitation and

emission transitions of Sm3+:V4+ions [102-103]. The possible energy

transfer happens from 2E2T2 level of vanadium ion [104-105] to 6F1/2 and

6F9/2 of Sm3+ ions. Hence Sm3+ ion gets excited from 6F1/2 to 4F3/2 and 6F9/2

to 4M15/2 and diexcited to 4G5/2 through non radiative decay and there by

strengthens the emission transition from 4G5/2 of Sm3+ ions. This causes the

increases in the intensity of Sm3+ ions rather than the vanadium ions. The

various radiative properties are calculated from the luminescence spectra

are presented in Table 9.

~ 247 ~

Table.9: Various radiative properties of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

GLASS SAMPLES

Transitions

from 4G5/2

Smv0 Smv1 Smv2 Smv3 Smv4 Smv5

A(s-1) β% A(s-1) β% A(s-1) β% A(s-1) β% A(s-1) β% A(s-1) β%

6H5/2 56.28 14.39 61.84 14.87 58.96 14.52 57.08 14.16 57.37 14.26 57.44 14.28

6H7/2 200.16 51.20 212.32 51.05 209.65 51.63 208.74 51.79 207.45 51.56 208.67 51.87

6H9/2 108.62 27.78 114.75 27.59 111.26 27.40 110.87 27.51 110.82 27.54 109.61 27.25

6H11/2 25.91 6.63 26.98 6.49 26.19 6.45 26.35 6.54 26.69 6.63 26.55 6.60

AT =390.97 AT =415.89 AT =406.06 AT =403.04

AT=402.33

AT=402.27

~ 248 ~

Figure.12: Energy level diagram of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

The radiative properties of any of Sm3+ ions depends on the number

of facts such as network former or modifier of the glasses. The parameters

βr (i.e. the branching ratio) of the luminance transitions describe the lasing

power of the potential laser transition. Among various transitions of the

glass network 4G5/26H7/2 are found to have the highest values of βr valued

among all the glasses [106]. These transitions are considered as a possible

laser transition and indicate that the glasses exhibit better lasing action. For

better identification of luminescence properties of the prepared glasses,

chromaticity coordinates are calculated from the emission spectrum. The

~ 249 ~

CIE system characterizes the color by a two color coordinate x and y which

specify the point on the chromaticity diagram as shown in Fig 13. The pure

white color source coordinate is 0.33, 0.33. The two color coordinates x

and y are nearly 0.3197, 0.1666 as indicated in Table 10. This implies that

this material can be used for optical devices

Figure.13: The color space chromaticity diagram of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped glasses

~ 250 ~

Table.10: The color coordinates of Na2O-SiO2-ZrO2: Sm3+:V4+ codoped

glasses

4.5. Conclusions

1. The physical properties of the glasses vary non-linearly with

increase of the concentration of V2O5 which affected all related

physical parameters of the system.

2. The charactersation of the samples by XRD, EDS technique have

indicate that the glasses has amorphous nature and the samples

contained well defined and randomly distributed grains at different

phases.

3. The IR and Raman spectral studies give valuable information

regarding bonding nature of different structural units in the glass

matrix.

4. The ESR spectrum confirms that the majority of vanadyl ions are

V4+ oxidation state.

S.No Glass

samples Color Coordinates

X Y

1 Smv0 0.2365 0.1074

2 Smv1 0.2476 0.1086

3 Smv2 0.3056 0.1666

4 Smv3 0.3022 0.1626

5 Smv4 0.2826 0.1546

6 Smv5 0.3197 0.1803

~ 251 ~

5. The optical absorption spectra could successfully explain J-O

parameters of Sm3+ ions that indicate the highest covalent

environment exits in the glass network.

6. According to the luminescence spectra, the highest value for

4G5/26H7/2 transition among various other transitions in the glass

system resulting the greatest value indicating that these glasses

exhibit better lasing action.

~ 252 ~

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