- Email: [email protected]
Structural and photoluminescence studies of Eu3+ doped l -Tartaric single crystal through evaporation technique
Journal of Molecular Structure 1085 (2015) 115–120
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Structural and photoluminescence studies of Eu3+ doped L-Tartaric single crystal through evaporation technique P.V. Prasad a, T.K. Visweswara Rao a, Ch. Satya Kamal a, S. Rajya Lakshmi a, R.K. Ramachandra a,⇑, V. Sudarsan b, M.C. Rao c, P.S.V. SubbaRao d a
Crystal Growth and Nano Science Research Centre, Department of Physics, Government College (A) Rajahmundry, Andhra Pradesh, India Chemistry Division, Baba Atomic Research Centre, Mumbai, India Department of Physics, Andhra Loyola College, Vijayawada, India d Department of Physics, Andhra University, Visakhapatnam, India b c
h i g h l i g h t s Eu
3+
doped LTA single crystals were synthesized by evaporation method.
XRD & HRXRD confirms prepared sample is good crystalline material. SHG efficiency of Eu
a r t i c l e
3+
doped LTA single crystal is 1.2 times that of pure KDP crystal.
i n f o
Article history: Received 26 October 2014 Received in revised form 26 December 2014 Accepted 30 December 2014 Available online 6 January 2015 Keywords: L-Tartaric acid Europium ions HRXRD Photoluminescence Lifetime component
a b s t r a c t Europium doped L-Tartaric acid; a non-linear optical single crystal was grown by slow evaporation solution growth method. The grown crystal was characterized by XRD for phase analysis, HRXRD for crystalline perfection, functional group by FTIR spectroscopy and powder SHG measurement for getting an estimate of NLO efficiency. The emission spectrum of Eu3+ doped L-Tartaric acid obtained after excitation at 394 nm and corresponding excitation spectrum by monitoring at 615 nm emissions. The decay curve is recorded corresponding to the 5D0 level of Eu3+ from tartaric acid doped with europium ions. The transparency of the crystal shows >90%, thermal analysis shows that the crystal to be thermally stable up to 189 °C and estimated atomic elemental composition in grown crystal with EDAX. L-Tartaric acid with chiral structure acts as a good host material for probing Eu3+ ions in synthesis of luminescent materials. Ó 2015 Elsevier B.V. All rights reserved.
Introduction The modern world is witnessing revolutionary advancements in the various aspects of science and technology. Every new day is suppressing its predecessor by some new achievements that require novel ideas leading towards the exploration of new materials for emerging fields, which were hitherto unknown [1]. Organic nonlinear materials are attracting a great deal of attention as they have large optical susceptibilities inherent ultra-fast response times and high optical thresholds for laser power as compared with inorganic materials. A number of such materials have been reported in the literature for their potential application [2,3]. Lanthanide doped non-linear optical (NLO) single crystals
⇑ Corresponding author at: Government College (A), Rajahmundry 533 105, Andhra Pradesh, India. Tel.: +91 0883 2478736. E-mail address: [email protected] (R.K. Ramachandra). http://dx.doi.org/10.1016/j.molstruc.2014.12.086 0022-2860/Ó 2015 Elsevier B.V. All rights reserved.
play a critical role in many technological applications. Due to the unique electronic structure of lanthanides, they have a wide variety of optical applications, including lasers, solar-energy converters and optical amplifiers. Hence, the search of new non-linear optical materials has been increased in recent times [4–7]. Many attempts were made to understand the interaction between rare earth and host materials electronic states and the influence in optical properties [8]. Many researchers are attracted towards new organic NLO materials possessing large dipole moment and with chiral structures. L-Tartaric acid (LTA) is chiral and its other complexes are known to possess good NLO properties [9–12]. In tartaric acid single proton ionization is easy, that Europium ions (Eu3+) must be replacing the protons of carboxyl group and forming (ACOO)3:Eu3+ bindings [13,14]. In the present work, Eu3+ doped LTA single crystals are prepared by using slow evaporation method and characterized by using different techniques. The grown crystals were subjected to powder
116
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
XRD to estimate the crystal structure and space group. The crystalline perfection was examined by HRXRD analysis. The functional groups are confirmed by FT-IR studies. The dopant of grown crystal was confirmed with EDAX and also analyzed the thermal stability. In addition to that the optical properties of the crystals are studied using second harmonic generation (SHG) efficiency. To the best of our knowledge no one reported the growth of LTA single crystals doped with rare earth ions. Experimental study and characterizations Crystal growth LTA and Europium nitrate (Eu(NO3)3) were purchased from Merck Chemicals, India. All of the chemical reagents used in this experiment were analytical grade and used without further purification. Single crystals of Eu3+:LTA were grown from aqueous solution by slow evaporation method. 0.1 mol% of solution has been prepared by using Eu(NO3)3 with double distilled water. The required amount of LTA acid are added and stirred continuously for 3 days. The prepared solution was filtered and kept undisturbed at constant temperature bath at 34 °C. Good quality crystals were obtained by spontaneous nucleation and within a span of 36 days, the crystals were harvested. Fig. 1 shows (a) bulk Eu3+ doped LTA crystal and (b) polished Eu3+ doped LTA single crystal.
its slit. FT-IR spectra were recorded using Perkin Elmer BX spectrometer in the range 400–4000 cm 1 using KBr pellets. Photoluminescence studies All luminescence measurements were carried out at room temperature by using an Edinburgh Instruments’ FLSP 920 system, having a 450 W Xe lamp and a ls flash lamp (60 W) as excitation sources. Red sensitive PMT was used as the detector. Approximately 20 mg of sample was mixed with few drops of methanol, made into slurry and spread over a glass plate, which was then dried under ambient conditions prior to luminescence measurements. All emission spectra were corrected for the detector response and all excitation spectra for the lamp profile. All emission measurements were carried out with a spectral resolution of 3 nm. Lifetime measurements were carried out using a 60 W micro-second flash lamp. Thermal analysis The Thermal analysis (TG/DTA) of the samples were performed using SII Nanotechnology Inc., Japan, EXSTAR 6200 instrument at a constant heating rate of 10 °C/min over a temperature range of 40–950 °C using alumina powder (10 mg) as a reference material. The sample of about 26.3 mg was uniformly spread over the balance pan. The degradation of samples was carried out under nitrogen atmosphere at a flow rate of 400 ml/min.
Powder X-ray diffraction & EDAX analysis UV–Vis spectra & SHG measurement Powder XRD measurements were carried out using a PW-1830 Philips Analytical X-ray diffractometer with nickel-filtered Cu Ka radiation (35 kV, 30 mA) at a scan rate 0.02° s 1 for the 2h angular range of 10–70° at room temperature. The elemental analysis has been carried out by energy dispersive X-ray analysis (EDAX) using an FEI Quanta 200 instrument. Multicrystal X-ray diffractometry & FTIR spectroscopy The crystalline perfection of the grown single crystals was characterized by HRXRD by employing a multicrystal X-ray diffractometer [15]. The well-collimated and monochromated Mo Ka1 beam obtained from the three monochromator Si crystals set in dispersive (+, , ) configuration has been used as the exploring X-ray beam. The specimen crystal is aligned in the (+, , , +) configuration. Because of dispersive configuration, though the lattice constant of the monochromator crystal(s) and the specimen are different, unwanted dispersion broadening in the diffraction curve (DC) of the specimen crystal is insignificant. The specimen can be rotated about the vertical axis, which is perpendicular to the plane of diffraction, with minimum angular interval of 0.4 arc sec. The DC was recorded by so-called x scan method, wherein the detector was kept at the same angular position 2hB with wide opening for
The optical transparency was checked by using a Perkin Elmer LAMBDA 35 UV–Vis spectrophotometer in the range 200–900 nm. The SHG behavior of powdered material was tested using Kurtz and Perry method (Kurtz & Perry, 1968), A KDP crystal was used as a reference. An Nd:YAG laser of fundamental wavelength 1064 nm, pulse width 10 ns, with a repetition rate of 10 Hz was used as a source. The laser radiation was made incident on the specimen sample and green output radiation from the specimen was detected by a photomultiplier tube coupled with a filter. SHG signals of the specimen crystal and the standard KDP were recorded. The signal from photomultiplier tube was used to assess the relative SHG efficiency of crystals. Results and discussion Powdered X-ray diffraction analysis Fig. 2 shows the powder X-ray diffraction pattern of Eu3+ doped LTA single crystals. All the peaks observed in the XRD pattern are characteristic of LTA with monoclinic crystal structure with space group P21. The unit cell dimensions were calculated from the least square fit of the XRD peaks and are found to be a = 6.201 Å,
Fig. 1. (a) Bulk Eu3+ doped LTA crystal. (b) Polished Eu3+ doped LTA single crystal.
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
117
Photoluminescence studies Eu doped L-Tartaric acid
(110)
2000
(⎯2 2 1 )
(⎯3 1 2 )
(121)
(102)
(201)
(101)
500
(⎯1 1 1 ) (111)
(100 )
1000
(⎯1 0 1 )
Intensity (c/s)
1500
0
10
20
30
40
50
60
70
2 θ (degree) Fig. 2. Powder XRD spectrum of Eu3+ doped LTA single crystal.
b = 6.015 Å and c = 7.730 Å. The values are in good agreement with those of undoped LTA (JCPDS Card No.33-1883) [16,17]. From these results it is inferred that Eu3+ doping do not have any effect on the crystal structure of the amino acid.
EDAX The presence of carbon, oxygen and europium is confirmed in Eu3+ doped LTA single crystal from the EDAX with SEM spectra as shown in Fig. 3. From the data it is clear that the amount of europium getting into the crystal is very evident.
HRXRD studies Before recording DC, to remove the non-crystallized solute atoms remaining on the surface of the crystal and to ensure the surface planarity, the specimen was first lapped and chemically etched in a non-preferential enchants of water and acetone mixture in 1:2 volume ratio. Fig. 4 shows the high resolution X-ray diffraction curve recorded for (1 0 0) diffraction planes using Mo Ka1 radiation for a typical Eu3+ doped LTA single crystal specimen. As seen in Fig. 4, the diffraction peak is quite sharp without any satellite peaks suggesting the absence of structural grain boundaries [18]. The full width at half maximum (FWHM) of the diffraction curve is 13 arc sec, which is very close to that of expected from the plane wave theory of dynamical X-ray diffraction [19]. The single sharp diffraction curve with very low FWHM indicates that the prepared sample is good crystalline material.
FT-IR analysis Fig. 5 shows the FT-IR spectra of undoped and Eu3+ doped LTA single crystal recorded in the range of 400–4000 cm 1. In pure LTA FT-IR spectrum shows a very strong peak observed at 1731 cm 1 which is characteristic of presence of C@O in the sample [20]. The weak peak at 1414 cm 1 is due to the combination of CAO stretching and OAH deformation [21]. The strong and broad peak at 3413 cm 1 is due to the presence of OAH stretching present with the carboxyl group. Although similar spectrum is observed for Eu3+ doped LTA, but a strong peak due to OAH group of carboxyl moiety was not observed. From this result it is inferred that Eu3+ must be replacing the protons of carboxyl group and forming (–COO )3 Eu3+ linkages [22].
Fig. 6 shows the emission spectrum of Eu3+ doped LTA single crystal excited at 394 nm. The spectrum consists of sharp peaks characteristic of the intra 4f transitions of Eu3+ ion. The peak at 591 nm is purely magnetic dipole in nature (DJ = ±1, J: total angular momentum quantum number) and at 615 nm is purely electric dipole in nature (force electric dipole transition, DJ = ±2) [22]. The relative intensity of electric and magnetic dipole transitions is found to be 2.4 for this sample. The results indicate that Eu3+ ions exist in a non-centro-symmetric environment in the sample. The weak and broad peak around 491 nm is arising due to emission from tartaric acid molecules. Corresponding excitation spectrum obtained by monitoring the 615 nm emission is shown in the inset of the same figure. Main peaks characteristic of intra 4f transitions of Eu3+ ions are only seen indicating that the energy transfer from host to Eu3+ ions is weak or negligible. In order to find the extent of incorporation of Eu3+ species in the lattice of tartaric acid, decay curve corresponding to the 5D0 level of Eu3+ has been recorded from the sample and is discussed in the following section. Decay curve of Eu3+ doped LTA single crystal Fig. 7 shows the decay curve of Eu3+ doped LTA single crystal corresponding to 5D0 level of Eu3+. The decay is found to be single exponential with a lifetime value of 3.4 ms. The lifetime value is characteristic of Eu3+ ions which are complexed with COO species and are uniformly distributed in the lattice. Thermal analysis Fig. 8(a) and (b) shows TG/DTA curves for both pure and Eu3+ doped LTA single crystals. The TG curve of pure and doped LTA shows that there is a weight loss of about 95% at 189 °C for doped and 187 °C for pure samples. The complete decomposition takes place for pure at 315 °C and for doped at 317 °C with 2.5% of end residue. It is clear from DTA curve that there is an endotherm 176 °C for pure and doped LTA samples. Due to doping there is a shift in decomposition temperature when compared with that of pure LTA. From these observations it is concluded that thermal stability of doped crystal is slightly increased which is useful for NLO applications [23]. UV–Vis–NIR transmittance The grown crystal transmission was checked in the range of 100–900 nm and is shown in Fig. 9. The UV transparency cutoff region is around 226 nm and there was no remarkable absorption in the entire region of the spectrum. Between 350 and 900 nm the transmittance is almost uniform (>90%). The high transmittance shows that crystal has good bulk optical quality and is free from volume defects such as inclusions, precipitates and bubbles [17]. High transparency is an important requirement for NLO materials. Second harmonic generation Second harmonic generation (SHG) test on Eu3+ doped LTA single crystal was performed by Kurtz powder SHG method [24]. The randomly oriented microcrystals of Eu3+ doped single crystal was irradiated using the fundamental beam of 1064 nm from Q-switched Nd: YAG laser. The energy of the incident laser beam is 2.5 mJ/pulse and pulse width about 10 ns with a repetition rate of 10 Hz. The second harmonic signal was about 12.0 mV. But the standard KDP crystals gave an SHG of 10 mV/pulse from the same input energy. Hence, it is seen that the SHG efficiency of Eu3+ doped LTA single crystal is 1.2 times that of pure KDP crystal.
118
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
Fig. 3. EDAX with SEM spectrum for Eu3+ doped LTA single crystal.
1000
100
800
MoK α 1
90
(+,−,−,+)
80
% Transmittence
Diffracted X-ray Intensity (c/s)
L-Tartaric + Eu
600
13
400
ii
200
Eu + L Tar Pure L Tar
70 60 50 40 30 20 10
0
0 -200
-100
0
100
200
Glancing Angle (arc sec)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (1/cm)
Fig. 4. Diffraction curve of Eu3+ doped LTA single crystal.
Fig. 5. FT-IR spectra of Pure and Eu3+ doped LTA single crystal.
The output could be seen as bright green color emission from the sample. The green emission confirmed the second harmonic gener-
ation in the grown crystals and the rare earth metal doping influenced the efficiency of undoped LTA [25].
119
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
3+
Emission spectrum of Eu doped LTA single crystal 5
7
D0
F2
Intensity
Intensity
12000
7
20000
F0
5
100
L6
80
10000
60
6000
300
%T
0 200
400
Wavelength (nm) 5 5
D0
7
D0
7
40
F4
F1
20
0
0
500
550
600
650
700
750
800
Wavelength (nm) Fig. 6. Emission spectrum of Eu
3+
200
400
600
800
1000
Wavelenth (nm) doped LTA single crystal. Fig. 9. Transmission spectrum of Eu3+ doped LTA single crystal.
1000
Conclusions
Decay curve of Eu3+ doped LTA
Intensity
100
10
1 1
3
2
4
Time (milli sec) Fig. 7. Decay curve of Eu3+ doped LTA single crystal corresponding to 5D0 level.
(a)
50 0
80
Pure Tartaric acid ------ TG ------ DTA
187 C
Acknowledgements
45 40 35 30
40
25 259 0 C
20 15
TG (ug)
DTA (uV)
60
20
10
0
0
315 C
-20
5
200
300
(a)
400
500
600
700
800
-5
References
900
Temparature (0C)
(b)
100 30
Eu doped L-Tartaric acid ------ TG ------ DTA
0
189 C 80
25 20
40
15 10
268 0 C
5
0
0
317 C 0
0
178 C
-20
(b)
-5 100
200
300
400
500
600
700
800
900
Temparature (0C) Fig. 8. TG/DTA curves of (a) pure and (b) Eu3+ doped LTA single crystal.
TG (%)
DTA (uV)
60
20
The authors are grateful to Dr. G. Bhagavannarayana, NPL Delhi for HRXRD studies. KRR is grateful to Dr. V. Sudarshan, Baba Atomic Research Centre (BARC), Mumbai for XRD and FTIR studies and Dr. SunilVerma, RRCAT, Indore for his valuable suggestions. He also wishes to thank Prof. P.K. Das, IASc, Bangalore and Dr. Ch. Mastanaiah, Principal, Government College (A), Rajahmundry, Andhra Pradesh for SHG measurements and Lab facilities.
0
0
176 C
100
In conclusion, slow evaporation technique has been used for preparation of Eu3+ doped LTA single crystal. Steady state luminescence and decay curve corresponding to 5D0 level of Eu3+ revealed that Eu3+ ions are incorporated in the crystal lattice. The crystallinity of the grown crystal has been confirmed by XRD analysis. The observed FT-IR spectrum of Eu3+ doped LTA single crystal confirms the incorporation of europium with COOA group in LTA crystal lattice. The crystalline perfection evaluated using HRXRD, indicates good crystalline quality of the single crystal. The thermal behavior indicated that sample is thermally stable up to 189 °C without any weight loss. Optical transmission study shows that the crystal has more than 90% of transmittance in visible and near infrared region. SHG conversion efficiency of Eu3+ doped LTA single crystal was found to be 1.2 times more efficient than KDP crystals.
[1] K.J. Arun, S. Jayalekshmi, J. Optoelectron. Adv. Mater. Rapid Commun. 2 (2008) 11. [2] M.D. Shirsat, S.S. Hussaini, N.R. Dhumane, V.G. Dongre, Cryst. Res. Technol. 43 (2008) 756. [3] S.S. Hussaini, N.R. Dhumane, V.G. Dongre, M.D. Shirsat, J. Optoelectron. Adv. Mater. Rapid Commun. 2 (2008) 108. [4] M.N. Palatnikov, I.V. Biryukova, N.V. Sidorov, A.V. Denisov, V.T. Kalinnikov, P.G.R. Smith, V.Ya. Shur, J. Cryst. Growth 291 (2006) 390. [5] U. Karunanithi, S. Arulmozhi, M. Dinesh Raja, J. Madhavan, Int. J. Eng. Res. Dev. 3 (2012) 51. [6] D. Hreniak, A. Speghini, M. Bettinelli, W. Strek, J. Lumin. 119 (2006) 219. [7] C. Zaldo, M. Rico, F. Diaz, J.J. Carvajal, Opt. Mater. 13 (1999) 175. [8] C.W. Thiel, Y. Sun, R.L. Cone, J. Mod. Opt. 49 (2002) 2399. [9] K. Moovendaran, B.R. Srinivasan, J. Kalyana Sundar, S.A. Martin Britto Dhas, S. Natarajan, Spectrochim. Acta A 92 (2012) 388. [10] M. Vimalan, T.R. Kumar, S. Tamilselvan, P. Sagayaraj, C. Mahadevan, Physica B 405 (2010) 3907. [11] S.A. Martin Britto Dhas, S. Natarajan, Cryst. Res. Technol. 42 (2007) 471. [12] A. Haja Hameed, C. Lan, J. Cryst. Growth 270 (2004) 475. [13] Y. Kubozono, A. Hirano, S. Nagasawa, Bull. Chem. Soc. Jpn. 66 (1993) 2166. [14] R.C. Bott, D.S. Sagatys, D.E. Lynch, Acta Crystallogr. C C49 (1993) 1150. [15] Krishan Lal, G. Bhagavannarayana, J. Appl. Cryst. 22 (1989) 209.
120
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
[16] S.A. Martin Britto Dhas, M. Suresh, G. Bhagavannarayana, S. Natarajan, J. Cryst. Growth 309 (2007) 48. [17] M.N. Rode, G.G. Muley, D.V. Meshram, S.S. Hussaini, V.G. Dongre, B.H. Pawar, M.D. Shirsa, J. Optoelectron. Adv. Mater. Rapid Commun. 3 (2009) 927. [18] G. Bhagavannarayana, R.V. Ananthamurthy, G.C. Budakoti, B. Kumar, K.S. Bartwal, J. Appl. Cryst. 38 (2005) 768. [19] B.W. Betterman, H. Cole, Rev. Mod. Phys. 36 (1964) 681. [20] V. Revathi, V. Rajendran, Int. J. Rec. Sci. Res. 4 (2013) 1332.
[21] M.N. Rode, S.S. Hussaini, G. Muley, B.H. Pawar, M.D. Shirsat, J. Optoelectron. Adv. Mater. Rapid Commun. 2 (2008) 12. [22] K. Moovendaran, V. Jayaramakrishnan, S. Natarajan, Photonics Optoelectron. 3 (2014) 9. [23] N. Vijayan, R. Remesh Babu, R. Gopalakrishanan, P. Ramasamy, M. Ichimura, M. Palnichamy, J. Cryst. Growth 273 (2005) 564. [24] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798. [25] M. Gunasekaran, N. Vijayan, R. Ramesh Babu, R. Gopalakrishnan, P. Ramasamy, C.W. Lan, J. Cryst. Growth 244 (2002) 194.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Structural and photoluminescence studies of Eu3+ doped L-Tartaric single crystal through evaporation technique P.V. Prasad a, T.K. Visweswara Rao a, Ch. Satya Kamal a, S. Rajya Lakshmi a, R.K. Ramachandra a,⇑, V. Sudarsan b, M.C. Rao c, P.S.V. SubbaRao d a
Crystal Growth and Nano Science Research Centre, Department of Physics, Government College (A) Rajahmundry, Andhra Pradesh, India Chemistry Division, Baba Atomic Research Centre, Mumbai, India Department of Physics, Andhra Loyola College, Vijayawada, India d Department of Physics, Andhra University, Visakhapatnam, India b c
h i g h l i g h t s Eu
3+
doped LTA single crystals were synthesized by evaporation method.
XRD & HRXRD confirms prepared sample is good crystalline material. SHG efficiency of Eu
a r t i c l e
3+
doped LTA single crystal is 1.2 times that of pure KDP crystal.
i n f o
Article history: Received 26 October 2014 Received in revised form 26 December 2014 Accepted 30 December 2014 Available online 6 January 2015 Keywords: L-Tartaric acid Europium ions HRXRD Photoluminescence Lifetime component
a b s t r a c t Europium doped L-Tartaric acid; a non-linear optical single crystal was grown by slow evaporation solution growth method. The grown crystal was characterized by XRD for phase analysis, HRXRD for crystalline perfection, functional group by FTIR spectroscopy and powder SHG measurement for getting an estimate of NLO efficiency. The emission spectrum of Eu3+ doped L-Tartaric acid obtained after excitation at 394 nm and corresponding excitation spectrum by monitoring at 615 nm emissions. The decay curve is recorded corresponding to the 5D0 level of Eu3+ from tartaric acid doped with europium ions. The transparency of the crystal shows >90%, thermal analysis shows that the crystal to be thermally stable up to 189 °C and estimated atomic elemental composition in grown crystal with EDAX. L-Tartaric acid with chiral structure acts as a good host material for probing Eu3+ ions in synthesis of luminescent materials. Ó 2015 Elsevier B.V. All rights reserved.
Introduction The modern world is witnessing revolutionary advancements in the various aspects of science and technology. Every new day is suppressing its predecessor by some new achievements that require novel ideas leading towards the exploration of new materials for emerging fields, which were hitherto unknown [1]. Organic nonlinear materials are attracting a great deal of attention as they have large optical susceptibilities inherent ultra-fast response times and high optical thresholds for laser power as compared with inorganic materials. A number of such materials have been reported in the literature for their potential application [2,3]. Lanthanide doped non-linear optical (NLO) single crystals
⇑ Corresponding author at: Government College (A), Rajahmundry 533 105, Andhra Pradesh, India. Tel.: +91 0883 2478736. E-mail address: [email protected] (R.K. Ramachandra). http://dx.doi.org/10.1016/j.molstruc.2014.12.086 0022-2860/Ó 2015 Elsevier B.V. All rights reserved.
play a critical role in many technological applications. Due to the unique electronic structure of lanthanides, they have a wide variety of optical applications, including lasers, solar-energy converters and optical amplifiers. Hence, the search of new non-linear optical materials has been increased in recent times [4–7]. Many attempts were made to understand the interaction between rare earth and host materials electronic states and the influence in optical properties [8]. Many researchers are attracted towards new organic NLO materials possessing large dipole moment and with chiral structures. L-Tartaric acid (LTA) is chiral and its other complexes are known to possess good NLO properties [9–12]. In tartaric acid single proton ionization is easy, that Europium ions (Eu3+) must be replacing the protons of carboxyl group and forming (ACOO)3:Eu3+ bindings [13,14]. In the present work, Eu3+ doped LTA single crystals are prepared by using slow evaporation method and characterized by using different techniques. The grown crystals were subjected to powder
116
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
XRD to estimate the crystal structure and space group. The crystalline perfection was examined by HRXRD analysis. The functional groups are confirmed by FT-IR studies. The dopant of grown crystal was confirmed with EDAX and also analyzed the thermal stability. In addition to that the optical properties of the crystals are studied using second harmonic generation (SHG) efficiency. To the best of our knowledge no one reported the growth of LTA single crystals doped with rare earth ions. Experimental study and characterizations Crystal growth LTA and Europium nitrate (Eu(NO3)3) were purchased from Merck Chemicals, India. All of the chemical reagents used in this experiment were analytical grade and used without further purification. Single crystals of Eu3+:LTA were grown from aqueous solution by slow evaporation method. 0.1 mol% of solution has been prepared by using Eu(NO3)3 with double distilled water. The required amount of LTA acid are added and stirred continuously for 3 days. The prepared solution was filtered and kept undisturbed at constant temperature bath at 34 °C. Good quality crystals were obtained by spontaneous nucleation and within a span of 36 days, the crystals were harvested. Fig. 1 shows (a) bulk Eu3+ doped LTA crystal and (b) polished Eu3+ doped LTA single crystal.
its slit. FT-IR spectra were recorded using Perkin Elmer BX spectrometer in the range 400–4000 cm 1 using KBr pellets. Photoluminescence studies All luminescence measurements were carried out at room temperature by using an Edinburgh Instruments’ FLSP 920 system, having a 450 W Xe lamp and a ls flash lamp (60 W) as excitation sources. Red sensitive PMT was used as the detector. Approximately 20 mg of sample was mixed with few drops of methanol, made into slurry and spread over a glass plate, which was then dried under ambient conditions prior to luminescence measurements. All emission spectra were corrected for the detector response and all excitation spectra for the lamp profile. All emission measurements were carried out with a spectral resolution of 3 nm. Lifetime measurements were carried out using a 60 W micro-second flash lamp. Thermal analysis The Thermal analysis (TG/DTA) of the samples were performed using SII Nanotechnology Inc., Japan, EXSTAR 6200 instrument at a constant heating rate of 10 °C/min over a temperature range of 40–950 °C using alumina powder (10 mg) as a reference material. The sample of about 26.3 mg was uniformly spread over the balance pan. The degradation of samples was carried out under nitrogen atmosphere at a flow rate of 400 ml/min.
Powder X-ray diffraction & EDAX analysis UV–Vis spectra & SHG measurement Powder XRD measurements were carried out using a PW-1830 Philips Analytical X-ray diffractometer with nickel-filtered Cu Ka radiation (35 kV, 30 mA) at a scan rate 0.02° s 1 for the 2h angular range of 10–70° at room temperature. The elemental analysis has been carried out by energy dispersive X-ray analysis (EDAX) using an FEI Quanta 200 instrument. Multicrystal X-ray diffractometry & FTIR spectroscopy The crystalline perfection of the grown single crystals was characterized by HRXRD by employing a multicrystal X-ray diffractometer [15]. The well-collimated and monochromated Mo Ka1 beam obtained from the three monochromator Si crystals set in dispersive (+, , ) configuration has been used as the exploring X-ray beam. The specimen crystal is aligned in the (+, , , +) configuration. Because of dispersive configuration, though the lattice constant of the monochromator crystal(s) and the specimen are different, unwanted dispersion broadening in the diffraction curve (DC) of the specimen crystal is insignificant. The specimen can be rotated about the vertical axis, which is perpendicular to the plane of diffraction, with minimum angular interval of 0.4 arc sec. The DC was recorded by so-called x scan method, wherein the detector was kept at the same angular position 2hB with wide opening for
The optical transparency was checked by using a Perkin Elmer LAMBDA 35 UV–Vis spectrophotometer in the range 200–900 nm. The SHG behavior of powdered material was tested using Kurtz and Perry method (Kurtz & Perry, 1968), A KDP crystal was used as a reference. An Nd:YAG laser of fundamental wavelength 1064 nm, pulse width 10 ns, with a repetition rate of 10 Hz was used as a source. The laser radiation was made incident on the specimen sample and green output radiation from the specimen was detected by a photomultiplier tube coupled with a filter. SHG signals of the specimen crystal and the standard KDP were recorded. The signal from photomultiplier tube was used to assess the relative SHG efficiency of crystals. Results and discussion Powdered X-ray diffraction analysis Fig. 2 shows the powder X-ray diffraction pattern of Eu3+ doped LTA single crystals. All the peaks observed in the XRD pattern are characteristic of LTA with monoclinic crystal structure with space group P21. The unit cell dimensions were calculated from the least square fit of the XRD peaks and are found to be a = 6.201 Å,
Fig. 1. (a) Bulk Eu3+ doped LTA crystal. (b) Polished Eu3+ doped LTA single crystal.
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
117
Photoluminescence studies Eu doped L-Tartaric acid
(110)
2000
(⎯2 2 1 )
(⎯3 1 2 )
(121)
(102)
(201)
(101)
500
(⎯1 1 1 ) (111)
(100 )
1000
(⎯1 0 1 )
Intensity (c/s)
1500
0
10
20
30
40
50
60
70
2 θ (degree) Fig. 2. Powder XRD spectrum of Eu3+ doped LTA single crystal.
b = 6.015 Å and c = 7.730 Å. The values are in good agreement with those of undoped LTA (JCPDS Card No.33-1883) [16,17]. From these results it is inferred that Eu3+ doping do not have any effect on the crystal structure of the amino acid.
EDAX The presence of carbon, oxygen and europium is confirmed in Eu3+ doped LTA single crystal from the EDAX with SEM spectra as shown in Fig. 3. From the data it is clear that the amount of europium getting into the crystal is very evident.
HRXRD studies Before recording DC, to remove the non-crystallized solute atoms remaining on the surface of the crystal and to ensure the surface planarity, the specimen was first lapped and chemically etched in a non-preferential enchants of water and acetone mixture in 1:2 volume ratio. Fig. 4 shows the high resolution X-ray diffraction curve recorded for (1 0 0) diffraction planes using Mo Ka1 radiation for a typical Eu3+ doped LTA single crystal specimen. As seen in Fig. 4, the diffraction peak is quite sharp without any satellite peaks suggesting the absence of structural grain boundaries [18]. The full width at half maximum (FWHM) of the diffraction curve is 13 arc sec, which is very close to that of expected from the plane wave theory of dynamical X-ray diffraction [19]. The single sharp diffraction curve with very low FWHM indicates that the prepared sample is good crystalline material.
FT-IR analysis Fig. 5 shows the FT-IR spectra of undoped and Eu3+ doped LTA single crystal recorded in the range of 400–4000 cm 1. In pure LTA FT-IR spectrum shows a very strong peak observed at 1731 cm 1 which is characteristic of presence of C@O in the sample [20]. The weak peak at 1414 cm 1 is due to the combination of CAO stretching and OAH deformation [21]. The strong and broad peak at 3413 cm 1 is due to the presence of OAH stretching present with the carboxyl group. Although similar spectrum is observed for Eu3+ doped LTA, but a strong peak due to OAH group of carboxyl moiety was not observed. From this result it is inferred that Eu3+ must be replacing the protons of carboxyl group and forming (–COO )3 Eu3+ linkages [22].
Fig. 6 shows the emission spectrum of Eu3+ doped LTA single crystal excited at 394 nm. The spectrum consists of sharp peaks characteristic of the intra 4f transitions of Eu3+ ion. The peak at 591 nm is purely magnetic dipole in nature (DJ = ±1, J: total angular momentum quantum number) and at 615 nm is purely electric dipole in nature (force electric dipole transition, DJ = ±2) [22]. The relative intensity of electric and magnetic dipole transitions is found to be 2.4 for this sample. The results indicate that Eu3+ ions exist in a non-centro-symmetric environment in the sample. The weak and broad peak around 491 nm is arising due to emission from tartaric acid molecules. Corresponding excitation spectrum obtained by monitoring the 615 nm emission is shown in the inset of the same figure. Main peaks characteristic of intra 4f transitions of Eu3+ ions are only seen indicating that the energy transfer from host to Eu3+ ions is weak or negligible. In order to find the extent of incorporation of Eu3+ species in the lattice of tartaric acid, decay curve corresponding to the 5D0 level of Eu3+ has been recorded from the sample and is discussed in the following section. Decay curve of Eu3+ doped LTA single crystal Fig. 7 shows the decay curve of Eu3+ doped LTA single crystal corresponding to 5D0 level of Eu3+. The decay is found to be single exponential with a lifetime value of 3.4 ms. The lifetime value is characteristic of Eu3+ ions which are complexed with COO species and are uniformly distributed in the lattice. Thermal analysis Fig. 8(a) and (b) shows TG/DTA curves for both pure and Eu3+ doped LTA single crystals. The TG curve of pure and doped LTA shows that there is a weight loss of about 95% at 189 °C for doped and 187 °C for pure samples. The complete decomposition takes place for pure at 315 °C and for doped at 317 °C with 2.5% of end residue. It is clear from DTA curve that there is an endotherm 176 °C for pure and doped LTA samples. Due to doping there is a shift in decomposition temperature when compared with that of pure LTA. From these observations it is concluded that thermal stability of doped crystal is slightly increased which is useful for NLO applications [23]. UV–Vis–NIR transmittance The grown crystal transmission was checked in the range of 100–900 nm and is shown in Fig. 9. The UV transparency cutoff region is around 226 nm and there was no remarkable absorption in the entire region of the spectrum. Between 350 and 900 nm the transmittance is almost uniform (>90%). The high transmittance shows that crystal has good bulk optical quality and is free from volume defects such as inclusions, precipitates and bubbles [17]. High transparency is an important requirement for NLO materials. Second harmonic generation Second harmonic generation (SHG) test on Eu3+ doped LTA single crystal was performed by Kurtz powder SHG method [24]. The randomly oriented microcrystals of Eu3+ doped single crystal was irradiated using the fundamental beam of 1064 nm from Q-switched Nd: YAG laser. The energy of the incident laser beam is 2.5 mJ/pulse and pulse width about 10 ns with a repetition rate of 10 Hz. The second harmonic signal was about 12.0 mV. But the standard KDP crystals gave an SHG of 10 mV/pulse from the same input energy. Hence, it is seen that the SHG efficiency of Eu3+ doped LTA single crystal is 1.2 times that of pure KDP crystal.
118
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
Fig. 3. EDAX with SEM spectrum for Eu3+ doped LTA single crystal.
1000
100
800
MoK α 1
90
(+,−,−,+)
80
% Transmittence
Diffracted X-ray Intensity (c/s)
L-Tartaric + Eu
600
13
400
ii
200
Eu + L Tar Pure L Tar
70 60 50 40 30 20 10
0
0 -200
-100
0
100
200
Glancing Angle (arc sec)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (1/cm)
Fig. 4. Diffraction curve of Eu3+ doped LTA single crystal.
Fig. 5. FT-IR spectra of Pure and Eu3+ doped LTA single crystal.
The output could be seen as bright green color emission from the sample. The green emission confirmed the second harmonic gener-
ation in the grown crystals and the rare earth metal doping influenced the efficiency of undoped LTA [25].
119
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
3+
Emission spectrum of Eu doped LTA single crystal 5
7
D0
F2
Intensity
Intensity
12000
7
20000
F0
5
100
L6
80
10000
60
6000
300
%T
0 200
400
Wavelength (nm) 5 5
D0
7
D0
7
40
F4
F1
20
0
0
500
550
600
650
700
750
800
Wavelength (nm) Fig. 6. Emission spectrum of Eu
3+
200
400
600
800
1000
Wavelenth (nm) doped LTA single crystal. Fig. 9. Transmission spectrum of Eu3+ doped LTA single crystal.
1000
Conclusions
Decay curve of Eu3+ doped LTA
Intensity
100
10
1 1
3
2
4
Time (milli sec) Fig. 7. Decay curve of Eu3+ doped LTA single crystal corresponding to 5D0 level.
(a)
50 0
80
Pure Tartaric acid ------ TG ------ DTA
187 C
Acknowledgements
45 40 35 30
40
25 259 0 C
20 15
TG (ug)
DTA (uV)
60
20
10
0
0
315 C
-20
5
200
300
(a)
400
500
600
700
800
-5
References
900
Temparature (0C)
(b)
100 30
Eu doped L-Tartaric acid ------ TG ------ DTA
0
189 C 80
25 20
40
15 10
268 0 C
5
0
0
317 C 0
0
178 C
-20
(b)
-5 100
200
300
400
500
600
700
800
900
Temparature (0C) Fig. 8. TG/DTA curves of (a) pure and (b) Eu3+ doped LTA single crystal.
TG (%)
DTA (uV)
60
20
The authors are grateful to Dr. G. Bhagavannarayana, NPL Delhi for HRXRD studies. KRR is grateful to Dr. V. Sudarshan, Baba Atomic Research Centre (BARC), Mumbai for XRD and FTIR studies and Dr. SunilVerma, RRCAT, Indore for his valuable suggestions. He also wishes to thank Prof. P.K. Das, IASc, Bangalore and Dr. Ch. Mastanaiah, Principal, Government College (A), Rajahmundry, Andhra Pradesh for SHG measurements and Lab facilities.
0
0
176 C
100
In conclusion, slow evaporation technique has been used for preparation of Eu3+ doped LTA single crystal. Steady state luminescence and decay curve corresponding to 5D0 level of Eu3+ revealed that Eu3+ ions are incorporated in the crystal lattice. The crystallinity of the grown crystal has been confirmed by XRD analysis. The observed FT-IR spectrum of Eu3+ doped LTA single crystal confirms the incorporation of europium with COOA group in LTA crystal lattice. The crystalline perfection evaluated using HRXRD, indicates good crystalline quality of the single crystal. The thermal behavior indicated that sample is thermally stable up to 189 °C without any weight loss. Optical transmission study shows that the crystal has more than 90% of transmittance in visible and near infrared region. SHG conversion efficiency of Eu3+ doped LTA single crystal was found to be 1.2 times more efficient than KDP crystals.
[1] K.J. Arun, S. Jayalekshmi, J. Optoelectron. Adv. Mater. Rapid Commun. 2 (2008) 11. [2] M.D. Shirsat, S.S. Hussaini, N.R. Dhumane, V.G. Dongre, Cryst. Res. Technol. 43 (2008) 756. [3] S.S. Hussaini, N.R. Dhumane, V.G. Dongre, M.D. Shirsat, J. Optoelectron. Adv. Mater. Rapid Commun. 2 (2008) 108. [4] M.N. Palatnikov, I.V. Biryukova, N.V. Sidorov, A.V. Denisov, V.T. Kalinnikov, P.G.R. Smith, V.Ya. Shur, J. Cryst. Growth 291 (2006) 390. [5] U. Karunanithi, S. Arulmozhi, M. Dinesh Raja, J. Madhavan, Int. J. Eng. Res. Dev. 3 (2012) 51. [6] D. Hreniak, A. Speghini, M. Bettinelli, W. Strek, J. Lumin. 119 (2006) 219. [7] C. Zaldo, M. Rico, F. Diaz, J.J. Carvajal, Opt. Mater. 13 (1999) 175. [8] C.W. Thiel, Y. Sun, R.L. Cone, J. Mod. Opt. 49 (2002) 2399. [9] K. Moovendaran, B.R. Srinivasan, J. Kalyana Sundar, S.A. Martin Britto Dhas, S. Natarajan, Spectrochim. Acta A 92 (2012) 388. [10] M. Vimalan, T.R. Kumar, S. Tamilselvan, P. Sagayaraj, C. Mahadevan, Physica B 405 (2010) 3907. [11] S.A. Martin Britto Dhas, S. Natarajan, Cryst. Res. Technol. 42 (2007) 471. [12] A. Haja Hameed, C. Lan, J. Cryst. Growth 270 (2004) 475. [13] Y. Kubozono, A. Hirano, S. Nagasawa, Bull. Chem. Soc. Jpn. 66 (1993) 2166. [14] R.C. Bott, D.S. Sagatys, D.E. Lynch, Acta Crystallogr. C C49 (1993) 1150. [15] Krishan Lal, G. Bhagavannarayana, J. Appl. Cryst. 22 (1989) 209.
120
P.V. Prasad et al. / Journal of Molecular Structure 1085 (2015) 115–120
[16] S.A. Martin Britto Dhas, M. Suresh, G. Bhagavannarayana, S. Natarajan, J. Cryst. Growth 309 (2007) 48. [17] M.N. Rode, G.G. Muley, D.V. Meshram, S.S. Hussaini, V.G. Dongre, B.H. Pawar, M.D. Shirsa, J. Optoelectron. Adv. Mater. Rapid Commun. 3 (2009) 927. [18] G. Bhagavannarayana, R.V. Ananthamurthy, G.C. Budakoti, B. Kumar, K.S. Bartwal, J. Appl. Cryst. 38 (2005) 768. [19] B.W. Betterman, H. Cole, Rev. Mod. Phys. 36 (1964) 681. [20] V. Revathi, V. Rajendran, Int. J. Rec. Sci. Res. 4 (2013) 1332.
[21] M.N. Rode, S.S. Hussaini, G. Muley, B.H. Pawar, M.D. Shirsat, J. Optoelectron. Adv. Mater. Rapid Commun. 2 (2008) 12. [22] K. Moovendaran, V. Jayaramakrishnan, S. Natarajan, Photonics Optoelectron. 3 (2014) 9. [23] N. Vijayan, R. Remesh Babu, R. Gopalakrishanan, P. Ramasamy, M. Ichimura, M. Palnichamy, J. Cryst. Growth 273 (2005) 564. [24] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798. [25] M. Gunasekaran, N. Vijayan, R. Ramesh Babu, R. Gopalakrishnan, P. Ramasamy, C.W. Lan, J. Cryst. Growth 244 (2002) 194.