# Growth and Characterization of L-Glycinium Phosphate: A Promising Crystal for Opto – Electronics Applications

K Rajesh, P Praveen Kumar, A Mani

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K Rajesh, P Praveen Kumar, A Mani. Growth and Characterization of L-Glycinium Phosphate: A Promising Crystal for Opto – Electronics Applications. Mechanics, Materials Science & Engineering Journal, 2017, 9 (2), 10.2412/mmse.18.52.862. hal-01502490

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# Growth and Characterization of L-Glycinium Phosphate: A Promising Crystal for Opto-Electronics Applications

K. Rajesh¹, A. Mani²,³, P. Praveen Kumar²

1. Department of Physics, AMET University, 135, ECR Kanathur, Inida

2. Department of Physics, Presidency College, Chennai, India

3. Sri Venkateswaraa College of Technology, Sriperumbudur, India

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.18.52.862 provided by [Seo4U.link](https://linkages.seo4u.com/)

**Keywords:** NLO, mechanical, dielectric, LDT, Vicker's hardness, phosphate.

**ABSTRACT.** An amino acid based semiorganic nonlinear optical single crystal of L-Glycinium Phosphate (GLP) was grown by the slow solvent evaporation method at room temperature. The single-crystal XRD analysis shows that the grown crystals have a monoclinic structure. Fourier transforms infrared (FTIR) spectral analysis and UV-Vis spectral studies were also carried out. Microhardness mechanical studies show that the hardness number of a GLP single crystal decreases with the load as measured by the Vickers microhardness method. The dielectric properties of the grown crystal were analyzed by varying the applied frequency. The nonlinear optical properties were studied using the Kurtz and Perry powder method and the second harmonic generation efficiency was found to be 3 times higher than that of KDP crystals. Laser Damage threshold studies was carried out and ability of the crystal against intense laser beam was calculated.

**Introduction:** There are many potential practical applications for nonlinear optical single crystal in the field of opto electronics and photonics [1]. For optical switching materials having large nonlinearity is essential. But it is very difficult to find materials with large nonlinearities with lesser losses [2]. Organic materials are interesting candidates for nonlinear optical applications like optical switching and optical limiting [3]. Organic materials posses a conjugated system caused by nonlinear polarization that occurs because of the interaction of laser light with strong electromagnetic waves [4]. In this respect, organic amino acid crystals are the potential candidates for optical applications. Most of the amino acids are available in natural organic materials [5]. Semi organic materials which are derived from the combination of organic and inorganic materials are plays a major role in SHG and third order nonlinear optical application [6]. For finding a better NLO material, several attempts are made on many amino acids, particularly, L-Serine and L-Arginine [7, 8]. Among all these semiorganic crystals, L-Glycine is an interesting material from both the crystal engineering and supramolecular point of views. The L-Glycine gives much attention because it has higher second-harmonic generation efficiency than other organic crystals and KDP [9]. This present investigation is made on L-glycine Phosphate a new semiorganic NLO material. Various properties of the crystal like electrical, mechanical, surface threshold and SHG are discussed.

**Crystal Growth and synthesis.** Glycinium Phosphate single crystal was grown in aqueous solution of L-glycine and ortho phosphoric acid in ratio of 1:1 at room temperature. The solution was continuously stirred for 9 hours with the help of hot magnetic plate. The solubility of glycinium phosphate in water was gravimetrically analyzed and the solubility found to be increase with increase in temperature. The saturated solution then filtered and was allowed for complete evaporation at room temperature for few days. Seed crystals were obtained in a period of 13 days. The crystalline quality of the seed crystal was improved by successive recrystallization process. Optically transparently and
good quality bulk crystal was obtained after a period of 2 weeks days from the day of recrystallization process. The grown crystal with dimension of 12 × 12 × 2 mm³ was taken for further studies and is shown in Fig. 1.

<figure><img src="image_3.png" /><figcaption>Fig. 1. Photograph of as grown GLP crystal.</figcaption></figure>

## Result and discussions

**Single crystal X-ray diffraction study.** Single crystal X-ray diffraction study was carried out for finding the cell parameters and crystal structure of glycinium phosphate crystal using Enraf Nonius CAD-4/MACH 3 diffractometer, with MoKα. The glycinium phosphate crystal is belonging to monoclinic crystal system with the space group P2₁. Cell parameters and space group of the grown crystal found from single XRD are in good agreement with the reported value [10] and are shown in table 1.

<table><caption>Table 1. XRD data of GLP crystal.</caption><thead><tr><th>Cell Parameters</th><th>Present work</th><th>Reported Values</th></tr></thead><tbody><tr><td>a</td><td>9.619 Å</td><td>9.7920(10)</td></tr><tr><td>b</td><td>8.467 Å</td><td>8.4870(10)</td></tr><tr><td>c</td><td>7.621 Å</td><td>7.411(2)</td></tr><tr><td>Crystal system</td><td>monoclinic</td><td>monoclinic</td></tr><tr><td>α = γ</td><td>90°</td><td>90°</td></tr><tr><td>β</td><td>100.11</td><td>100.43(2)</td></tr><tr><td>Space group</td><td>P2<sub>1</sub></td><td>P2<sub>1</sub></td></tr></tbody></table>

**FT-IR Study.** In order to confirm functional groups present in GLP crystal, fourier transform infrared (FTIR) spectrum was recorded in the range 400–4000 cm⁻¹ using the Perkin Elmer Infrared spectrophotometer. L-Glycine Phosphate single crystal was powdered and made as pellet shaped and subjected to FT-IR analysis. The absorption peaks are observed in between 400 to 4000 cm⁻¹ and it is shown in figure.3. The very strong absorption peak at 3400 cm⁻¹ indicates the presence of primary amine in the grown crystal. NH₂ plane deformation of primary amine is observed at the absorption peaks 1594 cm⁻¹ and 1666 cm⁻¹. The P-O stretching frequency and deformation of Phosphate ion were
identified at the peaks 1113 cm⁻¹ and 500 cm⁻¹ respectively [11]. This confirms the presence of phosphate ion in the grown crystal lattice.

**UV-Visible analysis.** From the transparency window of the material one can easily find out the usefulness of the crystal in linear and nonlinear applications. The optical absorption spectrum of GLP crystal was recorded in the wavelength region 190 nm to 1500 nm and is shown in Fig. 4. The lower cutoff wavelength of the grown GLP crystal is found to be 224 nm. Less absorption was found in the visible region and the crystal has the superior transmittance in the entire UV-Vis spectrum. The absence of strong absorption in the entire visible range and good transmittance suggests that the grown GLP crystal is a useful material for the SHG applications [12]. Hence it is concluded that the grown crystal can be used for optoelectronic applications. The energy gap (Eg) of the grown GLP crystal was calculated as 2.26 eV.

<figure><img src="image_4.png" /><figcaption>Fig. 3. FT-IR spectrum of GLP Crystal.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 4. UV-Vis spectrum of GLP.</figcaption></figure>

**Laser Damage threshold study.** The Laser Damage Threshold (LDT) of a crystal is an important factor affecting its optical applications. It depends on the material specific heat, thermal conductivity of the crystal and optical absorption of the crystal. LDT measurement of the GLP crystal has been carried out using a Q-witched Nd:YAG Laser beam of wavelength 1.064 µm with the pulse width rate of 10 ns. The repetition rate of the measurement is 10 Hz. The Laser beam of focal length 0.5 mm is focused on the sample area of 0.7 mm. The LDT value of the grown crystal obtained from single shot method is found to be 4.27 GW/cm².

**Second Harmonic Efficiency.** The Nonlinear optical property of the grown crystal is studied by Kurtz-Perry powder technique [23]. The standard KDP crystal has been used as the reference material for the grown crystal. The input energy of the laser source was 5 mJ/pulse. The SHG output wave at 532 nm was collected by the mirror, collimated and focused on to an photomultiplier for detection. The output SHG signal of 59.4 mV was obtained from the GLP crystal, whereas, the KDP crystal
gave an output of 21.4 mV for the same input signal. Thus it is evident that the SHG efficiency of the
Glycinium Phosphate crystal is almost 3 times that the KDP crystal and the crystal is suitable for
device fabrication.

**Dielectric measurement.** Single crystals of GLP was subjected to dielectric measurements, A thin coating of graphite applied on both sides of the crystal to provide necessary electrical conductivity. The capacitance of the crystal was noted at different temperatures using applied frequencies varying from 50 kHz to 5 MHz. Fig.6. shows the dielectric constant as a function of log frequency varying with temperature. The dielectric constant initially decreases with the increasing frequency, and at low temperatures of 313 K and 323 K, the dielectric constant (εr) has a higher value then the higher temperature 343 K and 353 K. The magnitude of εr depends significantly on the degree of polarization and charge displacement of the grown crystal. The low dielectric loss in higher frequency range shows (fig.7) that the grown crystal has few defects. The variations in the dielectric constant and dielectric loss as functions of frequency for GLP crystal may be considered as a normal behaviour of dielectrics and it shows that the crystal posses some minimum defects, which will be useful in device fabrication [13].

<figure><img src="image_6.png" /><figcaption>Fig. 5. dielectric constant vers log f.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 6. Dielectric loss vers log f.</figcaption></figure>

**Microhardness study.** The micro hardness test were carried out with the load range from 5 to 50 g using the Vickers hardness tester Richert MD 4000E ultra fitted with a diamond pyramidal indenter. The indentations were made at room temperature with a constant indentation time of 10 s.

<figure><img src="image_8.png" /><figcaption>Fig. 7. Hardness plot of GLP.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 8. Meyer's graph.</figcaption></figure>

As micro cracks were observed at higher loads the maximum applied load was restricted to 40 g. The lower load is due to the poor compaction [14] and highly brittle nature of the GLP crystal, that they undergo severe cracking and fracture for higher loads. The root cause of fracture is on the basis of molecular packing and attachment energies in the crystal structure [15].

The Meyer's index number was calculated from the Meyer's law, which relates the load.
$$P = Kd^n \quad (1)$$

where K is the material constant and n is the Meyer's Index.

Fig. 8 shows the plot of mayer's, yields straight line graph (before cracking plastic deformation) which is in good agreement with Meyer's law. The obtained slope value n is 1.97 for (110) plane by using the method of least square fitting. According to Onitsch [16], the value of n for soft materials is above 1.6. In this case proves GLP belongs to soft organic material category.

**Summary.** Organic nonlinear optical single crystal of Glycinium Phosphate was successfully grown by slow evaporation technique used water as a solvent. Single crystal X-ray diffraction study confirmed that the grown crystal belongs to monoclinic crystal system with the space group P21. Various functional groups were presented in the crystal was confirmed by Fourier transform infra red spectrum. The superior transmittance of the crystal in the entire visible region suggests that the GLP crystal is suitable for second order nonlinear optical applications. The hardness of the material indicates that the material belongs to soft material category which is the important property of the NLO material. This implies that GLP single crystal is a good engineering material for device fabrications. The Laser Damage Threshold value of the grown crystal is found to be 4.27 GW/cm². Both dielectric constant and loss are decreases with increase in frequency will prove that the GLP crystal posses minimum defects. The NLO efficiency of the Grown GLP crystal is 3 times of that the KDP crystal and the crystal is suitable for opto-electronics device applications.

References

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Cite the paper
K. Rajesh, A. Mani, P. Praveen kumar, (2017). Growth and Characterization of L-Glycinium Phosphate: A Promising Crystal for Opto – Electronics Applications. Mechanics, Materials Science & Engineering, Vol 9. doi 10.2412/mmse.18.52.862