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Effect of optical, mechanical and thermal properties of bio-organic chlorophyll-a of Ficus religiosa added ADP optical single crystal: A Novel NLO material
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Short note
Effect of optical, mechanical and thermal properties of bio-organic chlorophyll-a of Ficus religiosa added ADP optical single crystal: A Novel NLO material
T
S. Senthilkumara, S. Chidambaramb, R. Manimekalaib,* a b
Department of Physics, Parisutham Institute of Technology and Science, Thanjavur-613006, Tamilnadu, India A.V.V.M. Sri Pushpam College (Autonomous), Poondi, 613 503, Tamilnadu, India
A R T IC LE I N F O
ABS TRA CT
Keywords: A1.Solution growth A2.Chlorophyll-a A3.Linear and non-linear optical
A 0.5 mol% of organic Chlorophyll-a of Ficus religiosa and inorganic ammonium dihydrogen phosphate are added to an aqueous solution to form a semi-organic Chl-a doped ADP (CHLAADP) single crystal, grown by slow evaporation method. CHLAADP is subjected to linear optical, nonlinear optical, mechanical and thermal studies. UV–vis-NIR is taken for analyzing and to identify the optical properties, in terms of the cutoff wavelength, band gap, refractive index, optical conductivity, extinction coefficient, and electrical conductivity of CHLAADP crystal. It is observed that the inclusion of Chl-a enhance the optical properties of ADP. Vickers microhardness analysis establishes that CHLAADP belongs to the soft material category, The Optical parameter analysis confirmed that, CHLAADP is preferred for optoelectronics applications. The organic material (Chl-a) doped ADP may also be applied in communications systems, optical computing and healthcare applications like medical imaging process under Photonics. In the current work, the researcher has adopted the innovative idea of organic(Chl-a) doped inorganic (ADP) to study the optical characteristics of dopant materials in terms of optical and electrical conductivity, its response to light and temperature have been fulfilled. These properties are found to be suitable for sensors, power grids, electronics and lenses. The study and results for the parameters of CHLAADP prove that it is suitable for optoelectronic applications.
1. Introduction Ammonium dihydrogen phosphate (NH4H2PO4) crystal is a remarkable and renowned inorganic material with allied nonlinear optical (NLO), antiferroelectric and dielectric properties. Ammonium dihydrogen phosphate has a wide range of applications such as parametric generators, electro-optic modulator, optical switches, optical storage devices, acoustic–optical devices, transducers and high speed optical information processing [1–4] etc. The hydrogen-bonded ADP lattice can easily admit both inorganic and organic dopants [5]. Since the literature survey, dopant of organic impurities increases the optoelectronics application of the ADP. Based on the above mentioned fact, it is planned to use ADP and Chl-a of Ficus religiosa as an additive agent to prepare crystal using slow evaporation technique. The optical and mechanical parameters of the Chl-a doped ADP crystal is compared with Chl-a doped KDP [6], it was
⁎
Corresponding author. E-mail addresses: [email protected] (S. Senthilkumar), [email protected] (S. Chidambaram), [email protected] (R. Manimekalai). https://doi.org/10.1016/j.ijleo.2020.164530 Received 16 December 2019; Received in revised form 22 February 2020; Accepted 8 March 2020 0030-4026/ © 2020 Published by Elsevier GmbH.
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Fig. 1. As grown CHLAADP crystal.
found that notable changes were made by the doped element and it is well suited for optoelectronic device fabrication. The grown crystal has been investigated through various techniques, namely UV–vis Spectroscopy, Fourier transforms infrared spectroscopy (FTIR), Single crystal X-ray Diffraction (single XRD), Vickers’s microhardness, Energy dispersive X-ray spectroscopy (EDAX), TGA/DTA, SHG and Photoluminescence analysis (PL). 2. Materials and Methods The prepared 1 mol% of ADP solution is added with 0.5 mol % of Chl-a, then it was stirred more than 5 hour continuously using a magnetic stirrer. The well prepared solution was shifted to Petri disk and perfectly closed and the solvent was kept at ambient temperature. The as grown crystal (CHLAADP) was harvested in the time taken of 7–9 days. Then the as grown crystal was sent through recrystallization processes repetitively. A high quality, good transparent single crystal was harvested and is shown in Fig.1 3. Results and discussion 3.1. Single crystal X -ray diffraction The single crystal X-ray diffraction study was carried out on CHLAADP crystals to determine the unit cell parameters and the crystal structure. The results reveal that the CHLAADP single crystals have a tetragonal structure with lattice parameter a = b = 0.753Å, c = 0.758Å, volume = 0.430m3 and belongs to the I42d space group. The grown CHLAADP crystal has been compared with the pure ADP crystal [7]. 3.2. EDAX analysis `The incorporation of Chl-a in ADP has been confirmed by employing energy dispersive spectroscopic (EDAX) technique using the OXFORD instrument. The grown CHLAADP crystals were powdered and subjected to EDAX analysis in the energy range between 0–10 KeV. From the observed peaks the presence of dopants such as carbon and magnesium was confirmed in the crystal lattice of ADP. The chemical elements of CHLAADP crystals are shown in Table 1. 3.3. FT-IR spectra analysis The FTIR spectrum of the CHLAADP crystals were analyzed by KBr pellet technique using Perkin Elmer Spectrometer. The observed FTIR spectrum is compared and is in good agreement with the previouss works reported in the literature [8–10], which confirms the inclusion of varies functional groups in the grown sample. The FTIR vibrational band assignments of pure ADP and CHLAADP crystals are compared in Table 2. The broadband, appearing at 3131 cm−1 corresponds to NH- vibrations of ammonium [9]. The band at 2408 cm-1 is assigned to P-H stretching. The NH- bending of NH4 in parent is shifted from 1707 to 1675 cm−1. The band at 1293 cm−1 indicates the combination of asymmetric bending vibration of PO4 with lattice. The bands at 1101 cm−1 and 910 cm−1 indicate the PO] bending vibration and P-OH vibrations. Although the FTIR spectrum of 0.5 mol % Chl-a doped ADP carries similar features as that of pure ADP, there is a clear evidence for the presence of Chl-a in the lattice of ADP. The broadband in the high energy region of the FTIR spectrum of CHLAADP is found to be narrower and shifted to 3131 cm−1. There is also a shift in all other Table 1 EDAX-spectrum of CHLAADP. Element
C
N
O
Mg
P
Total%
Weight% Atomic%
20.35 18.48
3.6 5.1
41.04 53.26
10.98 11.98
19.03 11.18
100 100
2
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Table 2 FTIR spectrum of CHLAADP crystal. Pure ADP [11]
CHLAADP
Functional Groups Assignment
3245 3127 2877 2371 1707 1447 1296 1105 916
– 3131 – 2408 1675 – 1293 1101 910
Asymmetric stretching mode of NH3+ N-H vibration of Ammonium, (O=) PO-H stretching P-H stretching N-H bending of NH4 Bending vibration of Ammonium (NH4) Combination of Asymmetric bending vibration of PO4 with lattice P = O bending vibration P-O-H bending vibration
bands compared to pure ADP [11]. A slight shift in the peak positions of CHLAADP is seen when compared to that of pure ADP and also the narrowing of the band in the high energy region show the dissimilar peaks of proof and confirms the incorporation of Chl-a into the ADP crystal lattice. 3.4. UV–vis-NIR spectral analysis The optical properties of grown CHLAADP single crystals were studied using UV–vis-NIR spectrophotometer in the range of 190 nm–1100 nm. The optical band gap of the CHLAADP single crystal was calculated from the absorption spectrum using the relation, (αhν)n=A(hν)-Eg), where A - the optical transition constant, h - Planck’s constant, ν- frequency of the incident beam, Eg - energy gap, n characteristic transition. The pure ADP has cutoff wavelength around 202 nm [11]. With Chl-a addition, the cutoff wavelength is increased to 422.4 nm, it may be due to the inclusion of additive. These absorption peaks confirm the existence of Chl-a in doped ADP lattice. The analysis of optical constants plays a vital role in identifying the crystal’s application for optoelectronics [12]. The Chl-a doped ADP crystal with increased cutoff wavelength and high transmittance is may found to be more advantageous in NLO materials and UV tunable lasers [13]. The direct energy band gap of pure ADP crystal is found to be 6.13 eV [11]. The direct band gap energy of CHLAADP crystal is 4.24 eV as shown in Fig. 2. Thus the dimnished energy band gap, perhaps due to the inclusion of Chl-a. The reflectance (R), absorption coefficient (α), extinction coefficients (K) and refractive indices (n) were calculated. The refractive index (2.24) was found to decrease as a result of Chl-a doping in ADP crystal when compared to chl-a doped KDP (3.4) [7] and hence CHLAADP has lower refractive index. These low refractive indexed materials are widely used in antireflection coating material for solar thermal devices and holographic data storage devices [14,15]. The optical conductivity (σ) for CHLAADP crystals were eval∝cn uated from the refractive index (n) and absorption coefficient (α) as follows: σ= 4π , where c represents the speed of light. The optical conductivity improves by means of an increase in photon energy which is broadly used in information processing and computing applications [16,17]. Optical parameters of the CHLAADP are shown in Table 3. 3.5. Mechanical studies The Vickers hardness number was studied using microhardness tests that are suitable to analyse the hardness of the crystal, and to 1.8544 P kg , where ‘P’ compute the mechanical strength it can endure [10]. The Vickers hardness number was calculated using: Hv= d mm2 and ‘d’ are the load in kg and average diagonal length of the indentation in mm. It is observed that the hardness number of CHLAADP crystal has increased from 46.3–66.1 up to 100 kg. The addition of Chl-a enhances the hardness value than that of pure ADP crystals [18,19]. The higher hardness number of the CHLAADP crystal indicates that larger stress is required to form dislocation, thus
Fig. 2. Tauc plot of CHLAADP crystal. 3
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Table 3 Optical parameters of CHLAADP crystal (*present work) (α -no data available). Parameters
Pure ADP [11]
CHLAKDP [7]
*CHLAADP
Cutoff wavelength (λ) Band Gap (Eg) (eV) Extinction coefficient (k) Refractive index (n) Reflectance (R) Optical conductivity (σop) Electrical conductivity (σel)
202 6.13 α α α α α
336 4.01 1.91 × 10−5 3.4 33.3 3.2 α
422.4 4.24 1.41 × 10−5 2.24 45 3.88 3.64
confirming the better crystalline perfection. A plot of log p versus log d (Fig.3) shows a straight line graph and its slope gives the work hardening index n and is found to be 2.15, if the material having the value of ‘n’ is above 1.6, those components are soft material category [20]. From the observed grown crystal ‘n’ value, it is confirmed that the grown CHLAADP crystal belongs to the soft material Hv {1 − (2 − n)}(12.5(2 − n )2 − n
group. Yield strength σv is computed using the relation σv = . The nature of the bonding between successive 2.9(1 − (2 − n )) atom is determined by stiffness constant. The stiffness constants are calculated by Wooster’s empirical relation C11 = Hv7/4 for various loads. All the calculated mechanical parameters are compared with pure KDP [21,22], shown in Table 4. 3.6. Thermal studies Fig.4 shows the TGA and DSC thermographs of CHLAADP crystal. The TGA curve clearly shows that there is no weight loss up-to 216 °C, indicating that the doped crystal is thermally stable in the temperature range, 50 °C–216 °C, pure ADP crystal’s thermal stability ranges between ambient temperature to 470 K, which is reported by various authors [23]. Above 216 °C – 890 °C, 42.85% of total weight loss takes place, which may be due to the decomposition of the ADP. Total weight loss of pure ADP was 13.5%, which is already reported by earlier authors. [24]. It was found that the decomposition temperature of the CHLAADP is increased when compared to pure ADP [8]. The DSC curve shows an endothermic peak at 216.9 °C for the pure ADP, which is reported by S. Goel. et al. [11], at 215 °C for CHLAADP crystal. Similar results were reported in xylenol orange doped ADP single crystals [8]. 3.7. Photoluminescence The intensity of photoemission is calculated as a function of wavelength as shown in Fig.5. In the PL analysis of pure ADP, a broad blue emission band at 419 nm was observed [8]. For the Chl-a doped ADP sample (CHLAADP), emission spectrum consisting of two peaks at 449.89 nm and 676.33 nm were observed. Besides the characteristic blue emission band for pure ADP, a red emission band centered at 676.33 nm was also observed for the CHLAADP. This red emission confirms the Chl-a inclusion in ADP lattice. 3.8. SHG efficiency The Kurtz and Perry powder sample analysis was attained to study the second harmonic generation efficiency of the grown crystal. The grown samples CHLBADP were subjected to SHG test. The sample powder was illuminated by Nd:YAG laser working at 1064 nm having the input of the1.1 mJ/pulse, width of 8ns and repetition rate of 10 Hz. The second harmonic signals generated in
Fig. 3. log d vs log p. 4
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Table 4 Mechanical parameters of CHLAADP crystal (α - no data available) (*Present work). Hardness Parameters
Pure ADP [21,22] *CHLAADP
n
K1 kg/m
1.98 2.15
α 47.3
K2 kg/m
A 35.2
Hv
81 55.5
Pm
A 100
Ps
α 25
Kc
β
(MNm−3/2)
(m−1/2)
0.0141 0.080
5744.66 697
Σv (MPa)
C11 (Pa)
27 1430
20.91 × 106 [22] 1138
Fig. 4. TGA/DTA curves of CHLAADP crystal.
Fig. 5. Photoluminescence spectra of CHLAADP crystal.
the grown samples were recognized from emission of green radiation. An output SHG signal of CHLBADP was compared with pure KDP. The SHG efficiency of the CHLBADP crystal was found to be 1.33 times that of KDP crystal. The output SHG efficiency has been found a hike in the present case of organic CHLAADP crystal and is more than that of earlier reported value for organic metals doped ADP [25], it is established in Table 5. This study corroborates that, the grown CHLAADP crystal may be a potent NLO material which Table 5 Comparison of SHG efficiency of CHLAADP crystal (*Present work). Crystal
SHG efficiency with respect to KDP
Pure ADP [22] ADP +1 mole% of KI [22] ADP +1 mole% of MgCl2 [22] ADP +1 mole% of LiCl2 [22] *CHLAADP
0.8772 0.9474 1.0877 1.0526 1.33
5
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
are used for the applications in second harmonic generation and electro-optic devices [25]. 4. Conclusion Good quality transparent single crystals (CHLAADP) of Chl-a doped ammonium dihydrogen phosphate (ADP) have been grown by the slow evaporation method at room temperature. From UV–vis-NIR analysis, it is seen that optical transparency and direct energy band gap of CHLAADP crystal is decreased. The optical parameters such as reflection, reflectance, absorption coefficient, electrical conductivity, refractive index and optical conductivity were computed from the above-mentioned analysis and hence it is precise candidate for optoelectronic applications in the field of lenses, electronics, holographic data storage utilities and antireflection coating material. The hardness parameter such as elastic stiffness, yield strength and Meyer’s index has been calculated. The thermal studies showed that the CHLAADP crystal was stable between ambient temperature and 216 °C. Above 216 °C–950 °C, the weight loss is ∼ 43%. The photoluminescence spectrum of the CHLAADP crystal is confirmed the blue and red emission centered at 449.89, 676.33 nm. The SHG efficiency of the CHLAADP is 1.33 times that of pure KDP, it delineates that the title material is more appropriate for NLO applications. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement The authors extend their heartfelt thanks to SAIF, IIT Chennai for providing single crystal –XRD facilities. We also express our thanks to St. Joseph College and National College, Trichy for spectral and EDAX studies. We express our thanks to SASTRA University (CARISM), Thanjavur, for thermal studies. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.ijleo.2020. 164530. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]
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6
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Short note
Effect of optical, mechanical and thermal properties of bio-organic chlorophyll-a of Ficus religiosa added ADP optical single crystal: A Novel NLO material
T
S. Senthilkumara, S. Chidambaramb, R. Manimekalaib,* a b
Department of Physics, Parisutham Institute of Technology and Science, Thanjavur-613006, Tamilnadu, India A.V.V.M. Sri Pushpam College (Autonomous), Poondi, 613 503, Tamilnadu, India
A R T IC LE I N F O
ABS TRA CT
Keywords: A1.Solution growth A2.Chlorophyll-a A3.Linear and non-linear optical
A 0.5 mol% of organic Chlorophyll-a of Ficus religiosa and inorganic ammonium dihydrogen phosphate are added to an aqueous solution to form a semi-organic Chl-a doped ADP (CHLAADP) single crystal, grown by slow evaporation method. CHLAADP is subjected to linear optical, nonlinear optical, mechanical and thermal studies. UV–vis-NIR is taken for analyzing and to identify the optical properties, in terms of the cutoff wavelength, band gap, refractive index, optical conductivity, extinction coefficient, and electrical conductivity of CHLAADP crystal. It is observed that the inclusion of Chl-a enhance the optical properties of ADP. Vickers microhardness analysis establishes that CHLAADP belongs to the soft material category, The Optical parameter analysis confirmed that, CHLAADP is preferred for optoelectronics applications. The organic material (Chl-a) doped ADP may also be applied in communications systems, optical computing and healthcare applications like medical imaging process under Photonics. In the current work, the researcher has adopted the innovative idea of organic(Chl-a) doped inorganic (ADP) to study the optical characteristics of dopant materials in terms of optical and electrical conductivity, its response to light and temperature have been fulfilled. These properties are found to be suitable for sensors, power grids, electronics and lenses. The study and results for the parameters of CHLAADP prove that it is suitable for optoelectronic applications.
1. Introduction Ammonium dihydrogen phosphate (NH4H2PO4) crystal is a remarkable and renowned inorganic material with allied nonlinear optical (NLO), antiferroelectric and dielectric properties. Ammonium dihydrogen phosphate has a wide range of applications such as parametric generators, electro-optic modulator, optical switches, optical storage devices, acoustic–optical devices, transducers and high speed optical information processing [1–4] etc. The hydrogen-bonded ADP lattice can easily admit both inorganic and organic dopants [5]. Since the literature survey, dopant of organic impurities increases the optoelectronics application of the ADP. Based on the above mentioned fact, it is planned to use ADP and Chl-a of Ficus religiosa as an additive agent to prepare crystal using slow evaporation technique. The optical and mechanical parameters of the Chl-a doped ADP crystal is compared with Chl-a doped KDP [6], it was
⁎
Corresponding author. E-mail addresses: [email protected] (S. Senthilkumar), [email protected] (S. Chidambaram), [email protected] (R. Manimekalai). https://doi.org/10.1016/j.ijleo.2020.164530 Received 16 December 2019; Received in revised form 22 February 2020; Accepted 8 March 2020 0030-4026/ © 2020 Published by Elsevier GmbH.
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Fig. 1. As grown CHLAADP crystal.
found that notable changes were made by the doped element and it is well suited for optoelectronic device fabrication. The grown crystal has been investigated through various techniques, namely UV–vis Spectroscopy, Fourier transforms infrared spectroscopy (FTIR), Single crystal X-ray Diffraction (single XRD), Vickers’s microhardness, Energy dispersive X-ray spectroscopy (EDAX), TGA/DTA, SHG and Photoluminescence analysis (PL). 2. Materials and Methods The prepared 1 mol% of ADP solution is added with 0.5 mol % of Chl-a, then it was stirred more than 5 hour continuously using a magnetic stirrer. The well prepared solution was shifted to Petri disk and perfectly closed and the solvent was kept at ambient temperature. The as grown crystal (CHLAADP) was harvested in the time taken of 7–9 days. Then the as grown crystal was sent through recrystallization processes repetitively. A high quality, good transparent single crystal was harvested and is shown in Fig.1 3. Results and discussion 3.1. Single crystal X -ray diffraction The single crystal X-ray diffraction study was carried out on CHLAADP crystals to determine the unit cell parameters and the crystal structure. The results reveal that the CHLAADP single crystals have a tetragonal structure with lattice parameter a = b = 0.753Å, c = 0.758Å, volume = 0.430m3 and belongs to the I42d space group. The grown CHLAADP crystal has been compared with the pure ADP crystal [7]. 3.2. EDAX analysis `The incorporation of Chl-a in ADP has been confirmed by employing energy dispersive spectroscopic (EDAX) technique using the OXFORD instrument. The grown CHLAADP crystals were powdered and subjected to EDAX analysis in the energy range between 0–10 KeV. From the observed peaks the presence of dopants such as carbon and magnesium was confirmed in the crystal lattice of ADP. The chemical elements of CHLAADP crystals are shown in Table 1. 3.3. FT-IR spectra analysis The FTIR spectrum of the CHLAADP crystals were analyzed by KBr pellet technique using Perkin Elmer Spectrometer. The observed FTIR spectrum is compared and is in good agreement with the previouss works reported in the literature [8–10], which confirms the inclusion of varies functional groups in the grown sample. The FTIR vibrational band assignments of pure ADP and CHLAADP crystals are compared in Table 2. The broadband, appearing at 3131 cm−1 corresponds to NH- vibrations of ammonium [9]. The band at 2408 cm-1 is assigned to P-H stretching. The NH- bending of NH4 in parent is shifted from 1707 to 1675 cm−1. The band at 1293 cm−1 indicates the combination of asymmetric bending vibration of PO4 with lattice. The bands at 1101 cm−1 and 910 cm−1 indicate the PO] bending vibration and P-OH vibrations. Although the FTIR spectrum of 0.5 mol % Chl-a doped ADP carries similar features as that of pure ADP, there is a clear evidence for the presence of Chl-a in the lattice of ADP. The broadband in the high energy region of the FTIR spectrum of CHLAADP is found to be narrower and shifted to 3131 cm−1. There is also a shift in all other Table 1 EDAX-spectrum of CHLAADP. Element
C
N
O
Mg
P
Total%
Weight% Atomic%
20.35 18.48
3.6 5.1
41.04 53.26
10.98 11.98
19.03 11.18
100 100
2
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Table 2 FTIR spectrum of CHLAADP crystal. Pure ADP [11]
CHLAADP
Functional Groups Assignment
3245 3127 2877 2371 1707 1447 1296 1105 916
– 3131 – 2408 1675 – 1293 1101 910
Asymmetric stretching mode of NH3+ N-H vibration of Ammonium, (O=) PO-H stretching P-H stretching N-H bending of NH4 Bending vibration of Ammonium (NH4) Combination of Asymmetric bending vibration of PO4 with lattice P = O bending vibration P-O-H bending vibration
bands compared to pure ADP [11]. A slight shift in the peak positions of CHLAADP is seen when compared to that of pure ADP and also the narrowing of the band in the high energy region show the dissimilar peaks of proof and confirms the incorporation of Chl-a into the ADP crystal lattice. 3.4. UV–vis-NIR spectral analysis The optical properties of grown CHLAADP single crystals were studied using UV–vis-NIR spectrophotometer in the range of 190 nm–1100 nm. The optical band gap of the CHLAADP single crystal was calculated from the absorption spectrum using the relation, (αhν)n=A(hν)-Eg), where A - the optical transition constant, h - Planck’s constant, ν- frequency of the incident beam, Eg - energy gap, n characteristic transition. The pure ADP has cutoff wavelength around 202 nm [11]. With Chl-a addition, the cutoff wavelength is increased to 422.4 nm, it may be due to the inclusion of additive. These absorption peaks confirm the existence of Chl-a in doped ADP lattice. The analysis of optical constants plays a vital role in identifying the crystal’s application for optoelectronics [12]. The Chl-a doped ADP crystal with increased cutoff wavelength and high transmittance is may found to be more advantageous in NLO materials and UV tunable lasers [13]. The direct energy band gap of pure ADP crystal is found to be 6.13 eV [11]. The direct band gap energy of CHLAADP crystal is 4.24 eV as shown in Fig. 2. Thus the dimnished energy band gap, perhaps due to the inclusion of Chl-a. The reflectance (R), absorption coefficient (α), extinction coefficients (K) and refractive indices (n) were calculated. The refractive index (2.24) was found to decrease as a result of Chl-a doping in ADP crystal when compared to chl-a doped KDP (3.4) [7] and hence CHLAADP has lower refractive index. These low refractive indexed materials are widely used in antireflection coating material for solar thermal devices and holographic data storage devices [14,15]. The optical conductivity (σ) for CHLAADP crystals were eval∝cn uated from the refractive index (n) and absorption coefficient (α) as follows: σ= 4π , where c represents the speed of light. The optical conductivity improves by means of an increase in photon energy which is broadly used in information processing and computing applications [16,17]. Optical parameters of the CHLAADP are shown in Table 3. 3.5. Mechanical studies The Vickers hardness number was studied using microhardness tests that are suitable to analyse the hardness of the crystal, and to 1.8544 P kg , where ‘P’ compute the mechanical strength it can endure [10]. The Vickers hardness number was calculated using: Hv= d mm2 and ‘d’ are the load in kg and average diagonal length of the indentation in mm. It is observed that the hardness number of CHLAADP crystal has increased from 46.3–66.1 up to 100 kg. The addition of Chl-a enhances the hardness value than that of pure ADP crystals [18,19]. The higher hardness number of the CHLAADP crystal indicates that larger stress is required to form dislocation, thus
Fig. 2. Tauc plot of CHLAADP crystal. 3
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S. Senthilkumar, et al.
Table 3 Optical parameters of CHLAADP crystal (*present work) (α -no data available). Parameters
Pure ADP [11]
CHLAKDP [7]
*CHLAADP
Cutoff wavelength (λ) Band Gap (Eg) (eV) Extinction coefficient (k) Refractive index (n) Reflectance (R) Optical conductivity (σop) Electrical conductivity (σel)
202 6.13 α α α α α
336 4.01 1.91 × 10−5 3.4 33.3 3.2 α
422.4 4.24 1.41 × 10−5 2.24 45 3.88 3.64
confirming the better crystalline perfection. A plot of log p versus log d (Fig.3) shows a straight line graph and its slope gives the work hardening index n and is found to be 2.15, if the material having the value of ‘n’ is above 1.6, those components are soft material category [20]. From the observed grown crystal ‘n’ value, it is confirmed that the grown CHLAADP crystal belongs to the soft material Hv {1 − (2 − n)}(12.5(2 − n )2 − n
group. Yield strength σv is computed using the relation σv = . The nature of the bonding between successive 2.9(1 − (2 − n )) atom is determined by stiffness constant. The stiffness constants are calculated by Wooster’s empirical relation C11 = Hv7/4 for various loads. All the calculated mechanical parameters are compared with pure KDP [21,22], shown in Table 4. 3.6. Thermal studies Fig.4 shows the TGA and DSC thermographs of CHLAADP crystal. The TGA curve clearly shows that there is no weight loss up-to 216 °C, indicating that the doped crystal is thermally stable in the temperature range, 50 °C–216 °C, pure ADP crystal’s thermal stability ranges between ambient temperature to 470 K, which is reported by various authors [23]. Above 216 °C – 890 °C, 42.85% of total weight loss takes place, which may be due to the decomposition of the ADP. Total weight loss of pure ADP was 13.5%, which is already reported by earlier authors. [24]. It was found that the decomposition temperature of the CHLAADP is increased when compared to pure ADP [8]. The DSC curve shows an endothermic peak at 216.9 °C for the pure ADP, which is reported by S. Goel. et al. [11], at 215 °C for CHLAADP crystal. Similar results were reported in xylenol orange doped ADP single crystals [8]. 3.7. Photoluminescence The intensity of photoemission is calculated as a function of wavelength as shown in Fig.5. In the PL analysis of pure ADP, a broad blue emission band at 419 nm was observed [8]. For the Chl-a doped ADP sample (CHLAADP), emission spectrum consisting of two peaks at 449.89 nm and 676.33 nm were observed. Besides the characteristic blue emission band for pure ADP, a red emission band centered at 676.33 nm was also observed for the CHLAADP. This red emission confirms the Chl-a inclusion in ADP lattice. 3.8. SHG efficiency The Kurtz and Perry powder sample analysis was attained to study the second harmonic generation efficiency of the grown crystal. The grown samples CHLBADP were subjected to SHG test. The sample powder was illuminated by Nd:YAG laser working at 1064 nm having the input of the1.1 mJ/pulse, width of 8ns and repetition rate of 10 Hz. The second harmonic signals generated in
Fig. 3. log d vs log p. 4
Optik - International Journal for Light and Electron Optics 211 (2020) 164530
S. Senthilkumar, et al.
Table 4 Mechanical parameters of CHLAADP crystal (α - no data available) (*Present work). Hardness Parameters
Pure ADP [21,22] *CHLAADP
n
K1 kg/m
1.98 2.15
α 47.3
K2 kg/m
A 35.2
Hv
81 55.5
Pm
A 100
Ps
α 25
Kc
β
(MNm−3/2)
(m−1/2)
0.0141 0.080
5744.66 697
Σv (MPa)
C11 (Pa)
27 1430
20.91 × 106 [22] 1138
Fig. 4. TGA/DTA curves of CHLAADP crystal.
Fig. 5. Photoluminescence spectra of CHLAADP crystal.
the grown samples were recognized from emission of green radiation. An output SHG signal of CHLBADP was compared with pure KDP. The SHG efficiency of the CHLBADP crystal was found to be 1.33 times that of KDP crystal. The output SHG efficiency has been found a hike in the present case of organic CHLAADP crystal and is more than that of earlier reported value for organic metals doped ADP [25], it is established in Table 5. This study corroborates that, the grown CHLAADP crystal may be a potent NLO material which Table 5 Comparison of SHG efficiency of CHLAADP crystal (*Present work). Crystal
SHG efficiency with respect to KDP
Pure ADP [22] ADP +1 mole% of KI [22] ADP +1 mole% of MgCl2 [22] ADP +1 mole% of LiCl2 [22] *CHLAADP
0.8772 0.9474 1.0877 1.0526 1.33
5
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are used for the applications in second harmonic generation and electro-optic devices [25]. 4. Conclusion Good quality transparent single crystals (CHLAADP) of Chl-a doped ammonium dihydrogen phosphate (ADP) have been grown by the slow evaporation method at room temperature. From UV–vis-NIR analysis, it is seen that optical transparency and direct energy band gap of CHLAADP crystal is decreased. The optical parameters such as reflection, reflectance, absorption coefficient, electrical conductivity, refractive index and optical conductivity were computed from the above-mentioned analysis and hence it is precise candidate for optoelectronic applications in the field of lenses, electronics, holographic data storage utilities and antireflection coating material. The hardness parameter such as elastic stiffness, yield strength and Meyer’s index has been calculated. The thermal studies showed that the CHLAADP crystal was stable between ambient temperature and 216 °C. Above 216 °C–950 °C, the weight loss is ∼ 43%. The photoluminescence spectrum of the CHLAADP crystal is confirmed the blue and red emission centered at 449.89, 676.33 nm. The SHG efficiency of the CHLAADP is 1.33 times that of pure KDP, it delineates that the title material is more appropriate for NLO applications. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement The authors extend their heartfelt thanks to SAIF, IIT Chennai for providing single crystal –XRD facilities. We also express our thanks to St. Joseph College and National College, Trichy for spectral and EDAX studies. We express our thanks to SASTRA University (CARISM), Thanjavur, for thermal studies. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.ijleo.2020. 164530. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]
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