Chapter 5 Results and Discussion: Pure & Zn Doped Sodium ...shodhganga.inflibnet.ac.in/bitstream/10603/32066/12/12_chapter 5.pdf · the properties of potassium hydrogen phthalate

Chapter 5 Results and Discussion:

Pure & Zn2+ Doped Sodium Hydrogen Phthalate Single Crystals

Chapter 5 Results and Discussion: SP & ZSP Single Crystals

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CChhaapptteerr 55 Results and Discussion: Pure & Zn2+ Doped Sodium Hydrogen Phthalate Single Crystals

Abstract Single crystals of pure and zinc doped sodium phthalate (SP & ZSP) have been grown by slow evaporation solution technique (SEST) at room temperature. Zn-doped crystals were found to exhibit prominent morphological changes (rhombic bipyramidal to pentagon) in different crystallographic planes due to anisotropic distribution of dopant. XRD analysis revealed that presence of metallic dopant (Zn) in sodium phthalate lattice does not have any effect on the basic structure (orthorhombic) of the parent crystal. The presence of various functional groups and chemical bonding present in the crystals was identified and assigned qualitatively by Fourier transform infrared (FTIR) and Raman analysis. Incorporation of dopant into the crystalline matrix was confirmed quantitatively (2.72 ppm) by atomic absorption spectroscopy (AAS). UV-Vis studies indicate the low percentage of absorption in doped crystals in the visible region, thereby confirming the enhancement of non-linear optical (NLO) property. Photoluminescence (PL) spectra were found to show photoluminiscent peaks at 412 and 522 nm in pure SP crystals. It was found that due to Zn-dopant intensity of peak at 412 nm remain unchanged whereas intensity of peak at 522 nm increases with inhomogeneous broadening. From laser damage threshold studies, LDT values were found to be 0.32 and 0.25 GW/cm2 for pure and Zn-doped sodium phthalate crystals, respectively. Dielectric analysis revealed that on zinc doping dielectric tensor (ε33) and loss decreases significantly. Thermal analysis indicates that the melting point and thermal stability of Zn-doped sodium phthalate crystals is higher as compared to pure sodium phthalate crystals. 5.1. Introduction The semi-organic alkali hydrogen phthalate crystals are widely known for their application in the long-wave X-ray spectrometers, as a substrate for deposition of thin films of nonlinear materials, standard in volumetric analysis, etc [1-3]. Acid phthalate


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crystals are crystallized as non-centrosymmetric or centrosymmetric rhombic structures depending on the cation, since in 3D crystallographic frame, the bonding orientation of growth units is dramatically determined by these cations on the basis of the chemical bonding theory of single crystal growth [4-5]. Potassium acid phthalate (KAP), rubidium acid phthalate (RbAP), cesium acid phthalate (CSP), ammonium acid phthalate (NH4AP) crystals have found applications as crystal-analyzer in the light-gathering power spectrometer of long-wave radiation used for investigation of spectra and polarization of X-ray radiation. These crystals are used in quality and quantity analysis of light elements (Fe, Al, Mg, F and Si). Rubidium acid phthalate and thallium acid phthalate (ThAP) have been used in wide-band high-resolution soft X-ray spectrometers [6]. In this series, Sodium acid phthalate hemihydrate (SP) is also a good and promising candidate for SHG and various other applications in the acid phthalate family. Potassium acid phthalate crystals has a well-developed surface pattern on the (010) plane consisting of high and very low growth steps as can be easily observed by means of optical microscopy [7-8]. Similar type of growth steps can also be seen in SP crystals on the (001) plane. SP crystals has platelet morphology with perfect cleavages along the (001) plane. SP crystallizes in the orthorhombic system with space group B2ab with four molecules per unit cell (Z = 8) with cell dimensions: a = 6.75 Å, b = 9.31 Å, c = 26.60 Å [9]. SP consists of sodium ions, phthalate ions, and water molecules. The Na+ ion is surrounded by six O- atoms, four from the ionized carboxyl groups, one from an un-ionized carboxyl group, and one from the water molecule. The molecules are joined through an O-H---O hydrogen bond between the water molecule and two oxygen atoms of the ionized carboxylic group. Dielectric, ferroelectric, vibrational and optical properties of the pure SP crystals have been reported [10-12].

Influence of various dopants (Zn, Cu, Fe, Cr, alkali metals, Anthracene etc.) on the properties of potassium hydrogen phthalate crystals has been studied [13-17]. Addition of transition metals mainly increases the optical properties (SHG efficiency) of the potassium phthalate crystals with small changes in its lattice parameters as a result of lattice strain due to dopant substitution. Addition of anthracene also affects the fluorescence property and SHG efficiency of the potassium phthalate crystals. Alkali metal doping enhances the SHG efficiency of potassium hydrogen phthalate and it also affects its morphology.


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In the present chapter, transition metal (Zn) was used as a dopant in sodium phthalate crystals. Zn doping in potassium phthalate crystal grown by slow evaporation enhances SHG efficiency and various other properties [14]. Zn doping in Bis (thiourea) cadmium chloride (BTCC) also improves the optical property in the crystal without changing its basic crystal structure [18].The introduction of a small quantity of Zn2+ proved to play an important role in directing the anisotropic growth of SnO2 nanocrystals. Literature reveals that mostly doping studies were carried out with dopants having close atomic/ionic radii of host crystal. In the present investigation, the doping of the transition metal (Zn2+) was carried out intentionally to study the effect of size on the accommodation capability of the SP crystal, dependence of the nature of the additives on properties and their impact on the crystalline perfection which may in turn influence the optical properties, like SHG, transmittance etc.

In the present chapter, Pure and Zn doped SP crystals were grown by slow evaporation technique. To grow large single crystals seed rotation method has been used in which bidirectional rotation of seed crystal was performed by using a handmade circuit assembly. The aim of the present work is to grow optically transparent, good quality pure and Zn2+ doped SP crystals and to describe the influence of Zn2+ ions on the morphology and properties of pure SP crystals. Structural, dielectric, optical and thermal properties of pure and Zn-doped SP crystals are investigated in detail. 5.2. Synthesis and Crystal Growth

SP single crystals were grown from aqueous solution by slow evaporation technique by dissolving a stoichiometric amount of high-purity phthalic acid (AR grade) and sodium hydroxide in triple-distilled water. Resultant SP salt was purified by repeated recrystallization. A saturated aqueous solution of SP was prepared. The prepared solution was filtered with a micro filter. The crystallization took place within 30 days and large rhombic bi-pyramidal crystals of size upto 15x20x5 mm3 were grown as the major product on evaporation. These crystals were elongated in the [1 0 0] direction. For Zn doping in SP crystals 1M% conc. of Zn (II) in the form of Zn (NO3)2 were introduced in the initial aqueous growth medium as dopant and the single crystals of about 10x15x3 mm3 were harvested in around 40 days. It was observed that the morphology of pure SP crystal is hexagonal and that of Zn doped SP crystals is


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pentagon. Bulk crystals are grown using optimized growth parameters. Photographs of the as-grown and Zn doped SP crystals are shown in Figure 5.1.

Fig. 5.1: Pure sodium phthalate crystals grown by slow evaporation (1, 2) and seed rotation (5). Zn doped sodium phthalate crystals grown by slow evaporation (3, 4) and seed rotation (6)

It is well-known that changes in the morphology of crystals grown in doped solutions can be caused by the growth sites on the crystal being poisoned by the attachment of dopant species. In comparison with the rhombic bipyramidal morphology exhibited by pure SP crystals, Zn doping in the solution controls the growth rate in all directions and lead to produce pentagonal shape crystals with more transparency. There is anisotropic distribution of Zn impurity ions in SP lattice because absorption of Zn ion on any face of SP crystal will depend on the presence of cations (Na+) or anions (C8H5O4

-) on that face. Chances of attachment of Zn-impurity cations on the face having both cations and anions on it will be high and the impurity ions will block the growth on that face. On the other hand the face having only cations (Na+) on it will act as barrier for Zn impurity cations and the corresponding face will remain unchanged. This type of study on anisotropic distribution of impurity ions on a crystal has been carried out on KDP crystals [19]. The main reason for the change in crystal morphology is the modification of the growth rates along different crystallographic axes due to surface relaxation by zinc doping. Zn-impurity distribution in the pure sodium phthalate crystals induces strain fields in the SP crystal which are of two types: bulk strains and surface strains. Bulk strain occurs due to internal concentration stresses whereas surface strains occur because of relaxation of these internal concentration stresses [20]. This in turn gives rise to change in


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the positions of the atoms or ions in the surface layers in such a way that the system of strong bonds and the crystal structure remains unchanged. This whole phenomenon of surface relaxation in ZSP crystals lead to change in morphology of crystals [21]. 5.3. XRD Analysis Both pure and doped crystals were subjected to powder x-ray diffraction in two theta range 10-60o.The powder XRD patterns of Pure and Zn doped SP samples were refined using checkcell software and lattice parameters were evaluated. XRD patterns for both crystals are shown in Figure 5.2. All the peaks in XRD patterns are indexed with their corresponding hkl values.

Fig. 5.2: XRD patterns of pure and Zn doped sodium phthalate crystals

The unit cell parameters and space group are in good agreement with the

reported data and are tabulated in table 5.1 [9]. Table 5.1: Lattice parameters of pure and Zn doped sodium phthalate single crystals

Property a (Å)

b (Å)

c (Å)

α (degree)

β (degree)

γ (degree)

Volume (Å3)

Pure SP 6.6674(8) 9.2376(2) 26.4167(8) 90.00 90.00 90.00 1627.022 Zn doped SP 6.7288(3) 9.3292(3) 26.5979(8) 90.00 90.00 90.00 1669.665


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From the powdered X-ray analysis, it was confirmed that both pure and doped crystals crystallized in the orthorhombic structure. Narrow peaks indicate the good crystallinity of the material. No new peaks or phases were observed in XRD patterns by doping with transition metal zinc. Due to change in morphology, slight change in intensity of some peaks were observed as a result of doping while the intensity of two peaks at 21.1 and 26.9o gets reduced as a result of doping. There is also a slight change in the lattice parameters of the doped crystals. The slight change in the intensity of peaks and lattice parameters may be due to lattice distortion by doping in the parent crystal. The ionic radii of the dopant Zn2+ (88pm) is very small compared with that of Na+ (116pm). Hence it is reasonable that dopant can enter in the substitutional position in the host lattice without causing much distortion. The partial substitution of Na+ by Zn2+ leads to the formation of cation vacancies to maintain charge neutrality. Similar type of defects with cation vacancy has been observed in Mn doped KDP crystals [22].

5.4. Vibrational Spectroscopy FTIR and Raman spectra of the pure and Zn doped sodium phthalate crystals were carried out to study the characteristic vibrations of carboxylic acid, carboxylate, water molecules and phenyl rings present in the sodium phthalate crystals [11]. The observed FTIR and Raman spectra are given in Figure 5.3 and Figure 5.4, respectively. C-H stretching vibrations present in the phenyl rings is observed at 3071 cm-1

as a strong band in the Raman spectra. A strong IR and Raman band at 1600 cm-1 corresponds to the C-C stretching vibration of phenyl rings. Simultaneous activation of both IR and Raman band at same frequency gives evidence for charge transfer interaction present from donor to acceptor group through a single bond conjugated path. This charge transfer from donor to acceptor group make the molecule highly polarized which makes NLO properties possible in SP crystals [23].

C-C stretching in phenyl ring is also present at 1290 cm-1 as a strong IR band and at 1296 cm-1 as weak Raman band. Strong band at 1155 cm-1 in Raman spectra and at 1157 cm-1 in FTIR spectra corresponds to the C-H in plane bending vibrations of phenyl ring. Also a weak IR band at 1039 cm-1 and strong Raman band at 1040 cm-1 are responsible for C-H in plane bending vibrations. Vibrations present at 812 cm-1 in IR spectra and at 815 cm-1 in Raman spectra corresponds to the C-H out of plane bending of the phenyl ring. Strong band at 802 cm-1 and weak band at 798 cm-1 can also be assigned


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to the C-H out of plane bending vibrations. Band present at 702 cm-1 in the IR spectra is assigned to the O-H out-of-plane bending vibration in carboxylic group. Strong band at 1355 cm-1 and medium band at 1350 cm-1 corresponds to the C-O stretching vibrations present in the carboxylic group. In the IR spectra band present at 1574 cm-1 can be assigned to the asymmetric stretching vibrations of the carboxylate ion. The observed frequencies are found to be in good agreement with the reported values [11]. The doping of Zn in SP crystal matrix had no effect on the band position in Raman and FTIR spectra.

Fig. 5.3: FTIR spectra of pure and Zn doped sodium phthalate crystals

Fig. 5.4: Raman spectra of pure and Zn doped sodium phthalate crystals


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5.5. Atomic Absorption Spectroscopy The exact amount of Zn present in Zn-doped SP crystals was found by atomic absorption spectroscopy analysis by preparing the solutions of the doped crystals in aqua-regia. The results showed that the dopant concentration incorporated into the SP lattice was 2.72 ppm. It was seen that amount of Zn entered in sodium phthalate lattice is less than that of Zn present in the aqueous growth medium. This can be due to limited accommodation capability of SP lattice for dopant ions. 5.6. Optical Characterization 5.6.1. UV-Vis –NIR Analysis UV–Vis spectral study is a very useful technique to determine the transparency which is an important requirement for optically active material [24]. Transmission spectra are very important for any NLO material because a nonlinear optical material can be of practical use only if it has a wide transparency window. The UV-Vis spectrum (Figure 5.5a) of pure and Zn doped SP reveals that the cut off wavelength of both the samples is ~325nm. Absorption is minimum in the 325–1100 nm region. It is also inferred from the spectra that both pure and doped crystals have large transmission window in the entire visible region, and the Zn doped SP crystal has higher transmittance compared to pure SP crystal. This is because zinc belongs to the group (II B) of metals (Zn, Cd, Hg), which usually have high transparency in the UV region, because of their closed d10 shells [25]. Hence, the incorporation of Zn in the semi organic material (SP) as a dopant progressively improved the optical quality of SP crystals with higher transparency. This results in a high percentage of transmission in doped crystals, which is one of the most desired properties of the crystals used for the device fabrication and which will also increase the NLO property of doped crystals. The measured transmittance (T) was used to calculate the absorption coefficient (α) using the formula:

where, t is the sample thickness in mm.


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The absorption coefficient α of a crystalline solid obeys the relation:

where, Eg is the optical band gap of the crystal , n is an index determined by the nature of the electron transition during the absorption process, (n = 2 for allowed direct transition, and n = 1/2 for allowed indirect transition) and A is a constant nearly independent of photon energy, known as the disorder parameter [26]. For the present case n=1/2 was found to be best fitted for both pure and Zn2+ doped SP showing indirect transition nature of the material. Plot of (αhν)2 vs. photon energy for pure and Zn2+ doped SP is given in Figure 5.5b and optical band gap found to be 4.04 eV and 4.06 eV for SP and ZSP crystals, respectively. This shows that transition metal doping in SP enhances its optical quality and optical band gap which makes it more suitable for optical applications.

Fig. 5.5: (a) UV-vis. – NIR spectrum of pure and Zn doped SP crystals with increased transparency due to Zn-doping.(b) Variation of (αhν)2 vs. hν of the pure and Zn-doped SP crystals

5.6.2. Photoluminescence Analysis PL spectra of pure and Zn doped SP single crystals are given in Figure 5.6. Both pure and doped crystals were excited at 325 nm and spectra were recorded in the range 350-700 nm. PL spectra show a broad greenish emission of high intensity centered at 522 nm in addition to the small peak at 412 nm. Photoluminiscent peak of low intensity at 412 nm can be attributed to the intrinsic defects in the forbidden band region of pure SP crystals [27].


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Fig. 5.6: PL emission spectra for (a) pure sodium phthalate crystals and (b) Zn-doped sodium phthalate crystals in the wavelength region 350-700 nm

The emission band at 522 nm can be assigned to the transitions between filled π

to π* orbital of the metal and the ligand and radiative recombination between deep donors and shallow acceptors [28]. Zn-doping in these crystals gives rise to change in FWHM and area under both peaks. Zn-doping also causes inhomogeneous broadening of peaks which can be due to some energy levels created in the excited state and also due to high concentration of defects due to Zn-dopant. As discussed earlier, there is a creation of a number of cation vacancies because of dopants. Due to presence of these cation vacancies there is an increase in the PL emission property in visible region of the spectra for doped crystals. Increase in PL intensity of doped crystals may also be due to transfer of energy through the dopant energy level.

5.7. Non-linear Optical Characterization 5.7.1. SHG Efficiency The non linear optical conversion efficiency test was carried out for the grown crystals by the Kurtz powder technique [29]. SP crystals basically consist of a metal ion (Na+) surrounded by an organic ligand (phthalic acid). The organic ligand is more dominant in the NLO effect because it is a benzene derivative and a π- electron system. Metals in metal- organic coordination complexes not only help in increasing the SHG efficiency of


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SP crystals through metal-ligand (organic) bridging interactions but are also involved in NLO processes [30]. The π- electron cloud movement from donor to acceptor makes the molecule highly polarized, and the intramolecular charge transfer interaction is responsible for the NLO property in SP crystals. It has been reported that the SHG can be greatly enhanced by attaining the molecular alignment through inclusion complexation, therefore Zn doping in SP crystals was done to increase the SHG efficiency [31]. SHG efficiency of SP and ZSP are compared with KDP crystal powder of same particle size (63µm). For KDP value of SHG coefficient was found to be 4.8 mV while for SP and ZSP it was found to be 2.3 mV and 4.1 mV respectively. This implies that SHG efficiency of pure SP is almost half of KDP and for ZSP it is almost equal to that of KDP. This shows that zinc doping enhances the non linear optical property of sodium phthalate crystals to almost double; hence ZSP is more efficient material for NLO applications. As discussed above, Zn have high transparency in the UV region because of their closed d shell (d10). Therefore it is expected that substitution of Na by Zn in doped crystals will enhance the transparency and hence the SHG efficiency of ZSP crystals [24, 32]. 5.7.2. Laser Damage Threshold The laser damage threshold (LDT) studies were carried out for conventional solution grown pure and Zn-doped SP crystals using a continuous pulsed Nd: YAG (1064 nm) laser for a pulse width of 10 ns and pulse duration of 30 s. Both crystals were exposed to a laser beam on the (001) plane. The output of the laser beam was controlled by an attenuator and the beam is allowed to pass through a converging lens. The diameter of the beam spot on the sample was 1mm. During laser irradiation on increasing the energy density of the laser beam until the surface of the samples gets damaged and the corresponding energies were recorded [33]. During laser irradiation, localized heating due to absorption by the inclusion results in its vaporization, followed by damage to the crystal through local melting as well as fracture from thermal stresses [34-36]. The laser damage threshold for both crystals was calculated using the relation:

Power density (Pd) = E/τ πr2

where E is the energy (mJ), τ is the pulse width (ns) and r the radius of the spot (mm).


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Laser damage threshold values are found to be 0.32 GW cm-2 and 0.25 GW cm-2 respectively, for SP and ZSP single crystals.

5.8. Dielectric Analysis As discussed in the previous chapter, dielectric measurements for pure and Zn-doped crystals were carried out in c-direction. From these studies, dielectric tensor component (ε33) and dielectric loss was evaluated as a function of temperature and frequency. The variation of dielectric tensor (ε33) with frequency (10 mHz-10 MHz) in temperature range (RT-100 oC) for pure and Zn doped sodium phthalate crystals are shown in Figure 5.7a and Figure 5.7b, respectively.

Fig. 5.7: Frequency dependence of dielectric tensor (ε33) and dielectric loss at different temperatures for pure (a,b) and Zn doped (c,d) samples

It was observed that dielectric tensor decreases very rapidly at low frequencies, and then slowly as frequency increases, and finally it becomes saturated with further increase in frequency. At 100oC, value of dielectric tensor for pure sodium phthalate

(a) (c)

(d) (b)


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crystal is 405 at 10 mHz and decreases to 40 at 10MHz. Whereas for Zn doped sodium phthalate, at same temperature it is 63 at 10 mHz and decreases to 35 at 10MHz. This shows that on zinc doping, there is no much effect on dielectric tensor at high frequency but value at low frequency is highly affected. These graphs reveal that dielectric tensor decreased to very low value on zinc doping. This also indicates that the value of dielectric tensor increases with increase in temperature. As the net polarization present in the material is due to ionic polarization, electronic polarization, dipolar polarization and space charge polarization [37]. First two contributions do not decrease very significantly with rise in temperature. Contribution of decrease in dielectric tensor due to electronic polarization is very less. Dipolar polarization is also expected to decrease with temperature as it is inversely proportional to temperature. The contribution of space charge to polarizability depends on purity and perfection of crystals. At low temperature and high frequency we may take it as negligible. However it is significant in the low frequency region. As the temperature increases the contribution from space charge effect towards polarization may have tendency to increase. The dielectric loss with frequency is also measured for both pure and doped crystals shown in Figure 5.7c and Figure 5.7d, respectively. It is well observed that the dielectric loss decreases with increasing frequency. The low value of dielectric loss in Zn doped crystals as compared to pure ones indicates good quality of the doped crystals. The larger value of dielectric loss at lower frequencies may be attributed to space-charge polarization owing to charged lattice defects [38]. 5.9. Thermal Analysis The simultaneously recorded TG and DTA curves of both the pure and Zn (II)-doped SP crystal are displayed in Figure 5.8a and Figure 5.8b, respectively. The TGA curve gives useful information regarding the thermal stability and decomposition of the sample under investigation. The TG curve of pure SP shows a sharp weight loss of about 4.75% in the temperature range 92–127 oC. This is due to the loss of water of crystallization in the compound. This is followed by a major weight loss of about 30.23% occurring in two stages between 134 and 221 oC. The weight loss in these stages may be due to the decomposition and volatilization of the material. But, in the


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case of Zn (II) - doped crystal, the first stage of weight loss (4.48%) occurs in the temperature range 98–136 oC and the next stage of weight loss (38.86%) occurs in the temperature range 218-313 oC. Experimental values of weight loss of water matches very closely with the theoretical weight loss (4.86%) of half water molecule. The DTA curve of pure SP shows an endothermic peak at about 117 oC which is due to the loss of lattice water. It is followed by another peak at 211 oC which indicates the major decomposition of the material and this corresponds to the melting point of the pure SP. Meanwhile, the DTA curve of doped crystal shows peaks at about 124 and 295 oC and this may be attributed to the removal of lattice water and decomposition of the doped crystal. Hence, the TG and DTA studies clearly indicate that the melting point of the pure SP is significantly increased from 211 to 295 oC with the inclusion of Zn (II) in the SP crystal. To check the influence of dopant thermal stability of SP, the temperature corresponding to peak maximum of first stage of decomposition is taken into account for comparison. It was found that in Zn doped crystal this temperature increases from 117 oC to 124 oC. This increase of melting temperature may be due to smaller ionic radii of Zn (88 pm) than Na (116 pm). Smaller ionic radius of Zn can give more bonding interaction with phthalic acid therefore gives more thermal stability in ZSP [39]. It was observed that, after facing all decomposition or weight loss, residue left in pure SP crystals is 25 % whereas it is 40 % in ZSP crystals. Also there are more flat plateaus in doped crystals as compared to pure crystals. Therefore, ZSP crystals are more efficient for device applications requiring higher thermal stability of the crystals.

Fig. 5.8: TG-DTA curve of (a) pure and (b) Zn doped SP crystals with melting point at 211oC and 295oC respectively

� Endo � Endo


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5.10. Summary � Optically good quality single crystals of pure and zinc doped sodium phthalate

crystals were grown by slow evaporation technique at room temperature. � Bulk large size single crystals of both pure and doped crystals were grown by

seed rotation technique using seeds grown by slow evaporation technique. � Addition of zinc to the sodium phthalate crystals changes the morphology of

crystals from rhombic bipyramidal shape to pentagon with improved optical quality of doped crystals.

� XRD profile of crystals reveals that SP crystal lattice gets lattice strain because of substitution of Na+ by Zn2+ without changing its orthorhombic structure resulting cation vacancies in the original lattice.

� Various functional groups present in SP crystals were assigned and confirmed by FTIR and Raman analysis. It was found that there are very negligible changes in the spectra of doped crystals.

� From AAS studies 2.72 ppm of zinc was found to be present in the crystalline matrix of Zn doped SP crystals.

� UV-Vis-NIR studies reveals that there is no change in the band gap due to dopant though transmittance increases by Zn inclusion in SP lattice.

� From photoluminescence studies, peaks at 412 and 522 nm were observed in pure SP crystals. Intensity of peak at 522 nm increases by Zn dopant while that of peak at 412 nm remains unchanged.

� NLO study reveals that SHG efficiency of sodium phthalate crystals get double by zinc dopant.

� From Laser damage threshold studies, LDT values were found to be 0.32 and 0.25 GW/cm2 of SP and ZSP crystals, respectively.

� Dielectric tensor component (ε33) and loss gets reduced due to zinc doping in sodium phthalate crystals.

� From thermal studies, it was found that thermal stability and melting point of the SP crystal get increased as a result of Zn doping.


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Chapter 5 Results and Discussion: Pure & Zn Doped Sodium ...shodhganga.inflibnet.ac.in/bitstream/10603/32066/12/12_chapter 5.pdf · the properties of potassium hydrogen phthalate