Chapter 6

Spectroscopic and Glass transition investigations on ~ d ' ~ doped N ~ F - N ~ ~ o - B ~ o ~ glasses

6.1. INTRODUCTION

Fluoride glasses are most important for the optical fiber technolog? [ 1-41

due to their improved infrared transmission. But these glasses are marginall!

stable and the glass forming composition space is quite narrou. The

alkalihalohorate glasses [5-71 are also becomes most important because of the~r

last Ion conducting nature Also Alkalifluoroborate g l a s s are also well known

for their applications in phosphors. solar e n n u conveners and in a number of

electronic devices.

Shelh> and their co-uorken 181 prepared wide composition of NaF-Na:O-

i 3 : O : glasws and studied the refractive index, density and glass uansltlon

tcnlpr.rilturr.5 ofall glnsscs

Kr~shnunurth) et al (91 reported the dielectric properties of alkaliborate

glasses uith the transition metal (TM) ions doping in the glassy system. Their

conclusion illustrates that doping the TM ions in thc glass increases the a",

IremcndousI). Their IK investigation reveals b a t the TM ions doping in the

glass! s!srcrn changes thc s~ructure ofthe glasses.

Andndt ci al I lo] studied the electronic and thcnnal contributions of the

non. linear refmctivc indcx of ~ d " ion- doped fluoride glasses. Ihe! hate

concluded h a t h e glasscs having ~ d ' ' ions shorn smaller polarizabilib etkcts

Spectroscopic properties of Nd" doped heavy metal fluoride glasses were

studied by Amarnath [I I] and his coworkers. They studied the physical

properties of ~ d " doped glasses and they found that these types of glasses are

good for 1.05pn emission. Hanumanthu et al [I21 investigated the fluorescence

properties of ~ d " doped heavy metal fluoride glasses. They measured the

fluorescence spectra at different temperatures and they compared the

spontaneous emission probability and stimulated emission cross-section. The!

concluded that fluorozirconate glass is a better lasing material. Ratnakaram [I 31

and co-workers anal!,sed the optical absorption properties of Nd3- doped fluoro

horiitc glasses Opt~cal propenies of Nd'- doped fluorophosphat: glasses Here

rcponrd b! Stokouski [I41 and co-workers. The upconversion behavior of ~ d ' -

dupcd Ilut~r~~chlor~dc glasses irere rcponed b) Femandez [I 51 et a1 NaAal!. [ 161

and ccbuurhen rrported that ~ d " doped fluoroaluminate glasses are good for

In the present \tori,, structural, glass transition and optical propenies of

NJ" doped SaF-Na20B?0, glasses were studied.

6.2. EXPERIMENTAL DETAILS

7hc expcrimcntnl p m contains 1a.o divisions, the first one being the

prepatation of glasses through melt quenching method and h e second one is to

chatsftcrisc h e prcpwd glasses through mR. DSC. W-VlS methods and to

find the emission ptoperry of the Nd doped glasses.

6.2.1. GLASS PREPARATION

Nd" doped NaF-Na20-B203 glasses were prepared using high purit!

analar grade HtB03. Naf:. NalCO, and Nd201 in the composition range 25EjaF-

2SNa2CO3-(50-x)B203-xNdfi where x varies from 0 to 2. The codes along with

!he sample compositions are given in the following Table. 1

Table. I

Composition of ~ d " doped NaF-Na20-B203 glasses

- -

I he ~pproprlatc amounts of\\elghed chemicals here ground in a menu rv

produce 2Og each of glass rnl\turc The stochlometnc composltlons t ras LaLcn In

m open slllca cruc~blc and a! Lcpt In a electr~c mume furnace for heat treatment

Intllall), thc sample^ itere heated sloul) and ma~nmncd 4 3 0 ' ~ for 2 5 hours lor

the decorbon~sat~on of sod~umcorbonate and decompositton of bonc ac~d and

S.No

then the tempcraturc i s ralxd up to IOOO'C and maintained for half an hour. The

Sample Composition

crucibles were shaken licquentl! for the homogeneous mixing of all the

cons~iruents. ' hen the melt was quenched a1 room temperawe in air by pouring

ktwccn two stainless steel plates. The quenched glasses were in lilac in solour.

the glasses were cut into proper shape and polished for further characterization

88

I I Of- AO 25NaF-?SNa2C0,-50B203

OF/\ I / ISNab-25Na2C0349B203-1Nd203 1 111.4 1 5 2SNaF-?5Na2C0341.1BiOl- l .SNdfli

4 / OFA2 2SNaP-25Naf 0348B201-2Nd203

6.2.2. DETAILS OF STUDIES

The amorphous nature of the samples was confirmed by XRD studies in

Rigaku Miniflux table top spectrometer with Cu-Ka line of wavelength

i.- 1.54 18 A at the scanning rate of 2" per minute and 20 varies from 10" to 80"

rclracti\c indes ol' all thc prepared glasses were measured by Abbe's

rcfractomctcr by using the sodium vapour lamp. The density measurements of

all glasses \\,ere carried out by using the Archimedes's principle. The

rneasurcmen~s Here done using Dhona single pan balance and X!.lene as an inert

~mmcnion liquid. 'lhe densit! is obtained from the relation d cnl'r =

la (a-h)] a (densit! o f the Xylene). where 'a' is the weight of the glass sample in

.ilr. 'b ' i5 the \\eight i)f the glass sample when immersed in Xylene and the

dcns~t! of the X! lcne IS U.86 (gm cmi). lhe thermal studies \\.ere carried out b!

using hfe~tler 'Toledo Uiffercnt~al Scanning Calorimeter (DSC) in the

lcnlpcralurc riulgc ol'50.500"C' \r ith healing rate of 10 "C) minute in the Nitrogen

gas nrnio~phcrc.

l'he 1tr.d slructurc uf the ~ d " doped NaF-Na:O-B:Ol glasses ncrc

rludlcd through vihra~ional sprutroscop!. The FTIR spectra of all the san~ples

srcrr rccordcd bg using Sh~madzu F'TIR-8700 spectrometer in the wave number

rmgc of 4004000cnl" usirig KBr pellet technique. The optical spectra \rere

rwordcd in Shimadxu tu:V 1600 specvophotomcrcr in the \vavelength range ol'

400-950 nm, n e phololumln~cencc excitation and emission spectm t r t rr

r~ordcd using flwrrrccncc spccmmcr. (Model F4500, Hitachi, Japan). All

the spectra were recorded at room temperature. The physical properties of 1

%mol ~ d " doped glass is presented in the Table 2.

Table. 2

Physical Properties of lrnol% ~ d " ions doped OFAI glass

6.3. RESULTS AND DlSCLlSSlON

6.3.1. XRU ANALYSIS

The X.ra). diffruction pattern of os)~fluoborate glasses are shonn in Fig

I . 'Ihc XKL) pattern shokvs no sharp peaks indicating the absence of cr)stalline

nature. 'Ihis confirn~s the anlorphous nature of the glasses.

6.3.2, THERMAL ANALYSIS

' h e DSC thennogram shows that doping the 1 mol0~o Nd in the host \ \ i l l

increases the glass transition temperature (T,) while the excess doping decreases

S.No

1

2

Physical properties

Akerage molecular weight M (g)

Densit!. (@cmJ)

74.48

2.63 1

2.127

1.154

3.608

1.418

1.511

2.28

1.3 10

8.578

4.128

3 Kt,. ol'Ki( ions( 10" ions,'cm')

I / Poltron radiuslr. An)

5 Inter-ionic distance ( r , A") I 6 Field Strength (10" cm")

7 Refractive Index (n,,)

8

9

Dieleclric constant

t:.lcctronic. Polarizability (10"' cm')

Glass Molar Refracti! it! (crn3)

Reflcctiun Loss R Yo

T,. The DSC thennogram of OFAI, OFA2 are shown in the Fig. 2. The glass

crystalline onset is above 500°C. The variation of Tg with the glass composition

are shown in Table 3

Table. 3

Class transition temperatures of Nd doped NaF-Na20-B203 glasses.

6.5.3 FT IR SPECTRAL ANALYSIS

S.No

1

3 -.

lnfrarcd spectra of Sat.-Na:C)-B:O:. (OFAO. OFAI. OFA 2 ) arc s h m n in

I.lp. 3. All spectra she\+ the broad absorption band at 3440 cm", which is mainl!

duc hhdrox! l group5 prcssnt In the glasses and is anributed to the 0-H

\trs[chlrrp t ihrations.

Ihc IK spcctral \ brati ions ofthe borate glasses arc divided into thruc main

rcplons. Ihc tint region twcun kt\r.ecn 1200-1600 cm" which is due to

.tsymmetric. strc~ching rclasatton of the 9 - 0 bond stretching of trigonal BO:

units. Thc second ngion bctu.ecn ROO cm" and 1200 cm" is assigned to H . 0

hond stretching of the i30, units. Ihe third band is around 700 cm" is duc to R-

0 - B linkages in ~ h c borate net\+ork 117). The IR spectra show several pr.i~h\

which arc sharp, medium and broad. Thc broad bands arc due to combinatiorl of

Sample

OFAO

OFA 1

TXc)

440

445

3 ' OFAZ 435

Fig. 2. US(' Tbrrmoprrm olOFA1 and OFA2 glarscs

Fig. 3, FTlR rpcctra ofOF.40, OFAI, OFA2 glrsws

high degeneracy of vibrational states, thermal broadening of the lattice dispersion

and mechanical scattering of the powdered samples.

The vibration peaks at 2933, 2731 cm-' is assigned to the hydrogen

bonding present in the glasses. The broad absorption peak at and around 1340

cm" is ascribed to thc B-O stretching vibrations of trigonal ( ~ 0 ) ~ . units in

metaborate. pyroborates and orthoborate groups. This broad peak becomes much

broader in the OFAl than OFAO. OFAZ. The band at 1404 cm" is attributed to

the H-0' vibrations of the units attached to large segments of borate network. The

shoulder at IS12 cm" is due to B-0' bonds from isolated pyroborate groups [18].

'Ihe broad band around 1000 cm" is ascribed to the vibrations of some boron

atoms attached to non bridging oxygen in the form of Boa vibrations. This

absorption peak hccomes broader in OF.4 I . The band between 615 and 740crn"

is ass~gncd to the presence of pyrobonte and orthoborate units. The peaks of

I , I'IK rpcctru for all the glasses are shotvn in Table 4

6.3.4 OPTICAL ANALYSIS

'I'hc optical absorp~ion spectrum of Ioomol ~ d " doped NaF-NalO-B:O:

is S ~ I I U I I in IFigurc 4 III thc tratelength range of 400-950 nm. The spcctruni

o l '2n io lo~ ~ d " shorrs no change in the b q c e n t e r but the intensity of tht band is

highcr than the spc.ctrum which IS shoun in Fig. 4. In the present stud!

absorption spectrunr of IOohlol ~ d " doped NaF-Na?O-B:O: glass uas taken.

Table. 4

Peak Table of JTIR spectra of OFAO, OFAI , OFA2 glasses

Assignments

em") (cm") (cm.')

2 -

Hjdrogen bonding

4 5 1512 1512 B-0' bonds from isolated

Fyroborate groups

f , j I 4 W - 140.1 B-0' vibrations

B-0 strerchlng vibrat~ons

B-0 \ ibrat~ons. attached to B0,

untts

717 Presence of broborate goups

~engtym)

Fig. 4. Optical absorption spectrum of OFAI glass

The absorption transitions 4 ~ 3 , z , 4 ~ ~ n + 2 ~ 9 n , ' ~ m + ~ ~ 7 , 2 . 4 ~ q i 2 . 'H I I>Z .

4 4 4 4 ~ ~ 1 2 + 2 ~ 7 ~ . G ~ R , G912. G I ~ R + * K I ~ ~ + ~ G ~ , ~ + ~ D ~ ~ . 2~l ,q+2~, ,q 4 ~ q t 2 have been

observed and their energies, the experimental oscillator strength were calculated

from the absorptian spectra and the theoretical oscillator strength calculated b!

using Judd- Ofel1 [19-201 theoq through least square analysis method are

presented in Table 5. 7he weak bands are not taken in the least square analysis

because of the uncertainties in the determination of the experimental oscillator

strengths. ' h e hypersensitive band shows good agreement with the calculated

oscillator strength. The assignments of all transition were done on the basis of

Camall et. al..[?l Jand the reduced matrix elements also were taken from the

t'rmall ct, al..[?l]. In the calculation, because of overlapping of bands as

4 - I I 4 S; :- 4 1:- :.'~i, : - : G ~ . ! , 4 ~ l 1 2 - : ~ , , 2 + ' ~ P ? - 2 ~ ; . 2 . 'PI~-'D~:. the

corrcspond~ng reduced rilatris clcments \\ere added and the band is considered as

rtrc slriglc hand. I'hs calcula~cd J-O paramsten for different hosb with the 01.4 I

Jrc prcwn~cd In I'ahls h

Jorpenbcn and Keisli'ld 1112) have noted that the magnitude ot' R: is

ind~cativc of cobalcnt honding. while that of Rg is related lo the rigidit! at' rhs

host Ilsuall>. halide-containing glasses possess smaller value af'R: due to neah

Iixal ficlds and nminr lirrc\ridths [!3]. In the pnuenl work OI.'Al has Isss (2:

\.uluc which implies the less ccivalent character of the glass and thr high

symmeto of the local surroundings of the active ~ d " ' ions. The f& parameter

not only depend on the intensity of h e hypersensitive transition but also h a 3

Table. 5

Measured and Calculated oscillator strengths of lmolo/r ~d~ ions in

NaF-NaIO-&03 glPu

S.No Assignments

I , *Fi:

, 1 , . 1.' :.'llu:

I

Energy (em")

's. ..'I:. , .' I r . .

4 I 4 1.9 : I ' 13jb9 ,4641 i 3.52 l I

1 0.1515

i ? 4(i, ! :(;. : j I7094 16.271 i 16.201 1

rr : ' t i - : 1

19011 I

5.010 1 4,515

1 ' I ( i y : ' 19491

I 3.427 ! l.91V

! 1

x 1 . I ) , :*.I), ! I , 23256 j

2\24 I IlOO

. -. j j .\ nns 1 .VP!s 10"

11115

12422

Oscillator Strength

f-(lO3

3.921

5.363

f,k.( loo)

3.632

7.41 1

Table. 6

The J - 0 parameters of ~d~ ions in different host glasses

very large value for the reduced matrix elements / /u'~I ' . Nearly all the othcr

obsenbcd transitions. have small values for //L'!//'but other two reduced elements

:it '41: and 111 "I!' have significant values.

In the absorption spectrum, particularly the hypersensitive transition is

shined lo\\ards the higher \vavelength region (lower energy) due to

nephelausetic effect.

6.3.5.EMiSSION

The fluorescence spectrum of OFA I is shown in Fig. 5 . The emission was

found crntcred at 903 nm nhich is assigned to the ' ~ 1 . : + 4 ~ ~ : transition of ~ d " -

ion. 'Ihe escitation ~ a \ r l c n g t h used for this emission was 805 nm. From the

cmisbion data h! using J - 0 pardmeters the spontaneous emission probabilit! (.A=

hh3 s " ) and strrnulalcd rnlisaion cross-section (a =3.82 x 10"" cn?) of the

n~raaured c n l ~ s s ~ o n trar1~111on I S ca lcu la~~d.

6.4. CONCLllSlON

'Ihc F f I R sptri shot\ the neali band of 0-H vibrations in all the glasses.

I his Oti hwd rnulivalcs ~ h c nonradjative d m ) of emission of Nd ions and he

I I IK spectra of all thc glasses reieals the presence of &c Bl); and BC), units in

thc glassy s!.stcn). The h1ght.r taluc of L!, than the shotis rhar the glass 1s

\urtablc for the 0 0 0 3 ~ n 1 cmrhslon

. . - .-- . - - .- - - ' 1 . 1 ' I ' I '

A r' ...

. I . t . t . . -

@ - = 900 905 91 0 9 l S

W~ength(rn)

Fig. 5. Emission spectrum otOFAl gluc

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