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Home Search Collections Journals About Contact us My IOPscienceSynthesis and characterization of borate based and AgGaS2 materialsThis article has been downloaded from IOPscience. Please scroll down to see the full text article.2009 IOP Conf. Ser.: Mater. Sci. Eng. 2 012014(/1757-899X/2/1/012014)View the table of contents for this issue, or go to the journal homepage for moreDownload details:IP Address: 222.20.93.164The article was downloaded on 17/05/2013 at 10:45Please note that terms and conditions apply.Synthesis and characterization of borate based and AgGaS2 materialsR. DhanasekaranCrystal Growth Centre, Anna University-Chennai, Chennai 600 025.E-mail: rdhanasekaran@Abstract: In recent years, there has been tremendous development in the fabrication of suitablematerials for optoelectronic, laser, photovoltaic devices, acousto-optic, sonar and infrareddetectors applications. Mastering in synthesis, growth and characterization is an essentialrequirement for fully realizing the potential applications of the materials technology for theconstruction of novel devices for Laser, microwave, optoelectronic and other applications. Theanisotropy in the crystals gives them enhanced properties as required in the field of non-linearoptics. With the advent of laser sources, a nonlinear optical phenomenon has got tremendousinterest and nonlinear optical (NLO) materials play a key role in the development of lasertechnology. Because of the variety and complexity of the material systems involved, severalapproaches towards synthesis, growth and characterization have been developed during thepast decades. Laser materials can be classified into Inorganic, Organic and Semi organiccategories. Urea, DAST, mNA, POM, NPP, MAP are examples of organic family crystalswhere as L-Arginine phosphate (LAP), Zinc tris thiourea sulphate (ZTS), BTCC, ZCTCbelongs to semi organic class. Inorganic NLO crystals are Potassium titanyl phosphate (KTP),GdYCOB, KAB, Beta Barium Borate (BBO), LBO, KDP and LiNbO3. Synthesis andcharacterization of technologically important Borate based materials for NLO applications willbe reviewed. The raising demand for UV lasers has led to the development of various NLOmaterials. A series of borate materials – Rare earth calcium oxy borate (RECOB) with thegeneral chemical formula RECa4O(BO3)3with RE=Y,Gd, Nd, Sm, etc. are reported to besynthesized from their repective melts. The RECOB crystals are excellent NLO materials andwhen doped with ‘laser-active’ ions (Nd3+, Yb3+), they become efficient laser-host crystals. Thesingle crystals of YCOB were grown by flux technique using boron-tri-oxide as a flux. Thistechnique enables to grow YCOB crystals below its melting point (1510°C) . Powder XRDstudies were carried out on both the polycrystalline and single crystals of YCOB using theCuK X-rays ( =1.540 Å) at a scan rate of 0.05°/ min. The formation of YCOB was confirmedin both the samples. The powder XRD pattern of the grown crystals reveals the formation pureYCOB single phase. There are no excess peaks due to impurities or flux incorporations. UV-VIS-NIR studies were carried out on the as-grown crystals of YCOB which indicates thatYCOB crystals have a sharp cut-off around 220 nm and the crystal is highly transparent(>75%) from 220 – 1100 nm. The high transparent nature of the crystals from the deep UVregion enables it to be an excellent NLO material for UV applications. The results obtainedsuggest that flux technique is an excellent method to grow YCOB crystals. Crystal growth andcharacterization of novel borate materials like XAl3(BO3)4 where X = Nd, Yb and Er will bereviewed in detail.1. IntroductionThe propagation of electromagnetic waves through nonlinear media gives rise to vibrations at harmonics of the fundamental frequency, at sum and difference frequencies, and so on. In the optical frequency range, the same effect is observed when light waves propagate through weakly nonlinear optical dielectrics. When one or more sufficiently powerful beams of laser radiation pass through these dielectrics, the frequency of the radiation may be transformed to the second, third and higher harmonics and to combination (sum and difference) frequencies. In this way, the range of wavelengths generated by a certain laser source can be considerably increased. For instance, the second harmonic of the ruby laser radiation lies in the UV region ((λ= 0.3471 µm), whereas the second harmonic of the neodymium glass laser radiation lies in the green spectral region (λ= 0.53 µm). As early as 1961, FRANKEN and co-workers observed radiation at a doubled frequency when a ruby lasers beam was directed into a quartz crystal. However, because of phase mismatch of the waves at the fundamental and doubled frequencies upon propagation of the waves in a quartz crystal, the efficiency of conversion to the second harmonic proved to be very low, less than 10-10%. At the beginning of the 1960s, along with research into second harmonic generation first experiments were carried out on generation of optical radiation at combination frequencies, namely: sum frequency generation of radiation from two lasers, sum frequency generation of radiation from a laser and a noncoherent source, and difference frequency generation. It should be mentioned especially optical parametric oscillation, which is a nonlinear effect that allowing obtaining coherent continuously tunable optical radiation.The ferroelectrics ADP and KDP used in electroopical and acoustooptical devices were the first crystals applied for nonlinear frequency conservation techniques. However, some special nonlinear optical problems called for crystals with improved properties (high transparency in the UV region, higher non-linearity, lower hygroscopic, and so on). The resulting intensive scientific search for new materials has led to the synthesis of the number of new nonlinear crystals of high optical quality LiNbO3in 1964, Ba2NaNb5O15in 1967, proustite in 1967, LiIO3in1964, and others. The nonlinear optical crystals play a vital role in the photonics industry as they can perform frequency doubling, optical parametric oscillation (OPO) and optical parametric amplification (OPA). With the invention of several nonlinear optical (NLO) crystals the application of nonlinear optics is also expanding. Hence, the nonlinear optical crystals are being used for various applications including communications, medical surgery, data storage, etc. The properties of laser-diode-pumped solid-state lasers have been greatly improved and the output laser wavelengths with desired properties are also being made available by employing NLO crystals such as KTiOPO4(KTP), LiB3O5(LBO) and -BaB2O4 (BBO) [1]. So the single crystal growth for NLO applications has gained increasing importance in the field of materials research. The requirements for the excellent NLO crystal includes high nonlinear coefficient, moderate birefringence for phase matching, high transparency for the wavelength of interest, non-hygroscopic nature, high-laser-damage threshold, good mechanical properties and so on. Borate-based crystals are found to be excellent NLO crystals and now-a-days a large quantum of research is being focused on the growth and characterization of borate crystals [2]. Several borate crystals have high-laser-induced damage threshold. They are highly transparent in the UV and the visible regions. In the recent years, many types of NLO borate crystals have been reported, such as CsLiB6O10(CLBO), BiB3O6(BiBO), K2Al2B2O7(KAB), KBe2BO3F2 (KBBF) and YCa4O(BO3)3 (YCOB). Among them, the yttrium calcium oxy borate single crystals are grown by the melt techniques of crystal growth such as the Bridgmann and the Czochralski techniques [3–5]. The YCOB crystal belongs to the RECOB (with the general formula RECa4O(BO3)3) family of crystals with RE=Gd, Sm, Nd, Er, La and Y. These crystals have excellent nonlinear optical qualities and provide suitable sites for doping with laser active ions such as Nd3+, Yb3+, Er3+ and so on to facilitate its application in phosphor-based devices [6,7]. The flux growth of YCOB single crystals from thelithium carbonate flux was performed earlier and reported [8]. This paper reports the successful growth of YCOB single crystals from the self-flux (boron-tri-oxide flux) for the first time. The quality of the YCOB crystals has been improved by using the self-flux. The synthesis of the polycrystalline YCOB material, single crystal growth of YCOB and the characterization studies performed on the grown crystals are presented in detail. AgGaS2 is one of the attractive IR nonlinear optical materials for device applications due to its unique properties, including large nonlinear optical coefficients and appropriate birefringence. It is widely used for making nonlinear optical devices such as second harmonic generators, optical parametric oscillators and up-converters. The CVT growth of AgGaS2 materials and their characterizations are presented.2. Synthesis and preparation of YCOB materialThe starting material for crystal growth was prepared by mixing the high-pure chemicals of Y2O3, CaCO3and B2O3in platinum crucible. The mixture was carefully grounded and was taken in a platinum crucible. It was heated to 1000°C for 24 h. This was done to eliminate the carbon-di-oxide present in the mixture. The obtained product was again well-mixed in the platinum crucible and was heated to 1200°C for 24 h. The powder XRD studies confirm that the obtained product is the YCOB polycrystalline material. The polycrystalline YCOB powder was taken along with the boron-tri-oxide flux in the ratio of 1:2 (YCOB:B2O3) in a platinum crucible. The melting point of the YCOB material is reported to be 1510°C. But the YCOB polycrystalline powder is found to dissolve in the boron-tri-oxide flux in the temperature range of 1000–1030°C. Hence the thermal cycle was designed accordingly. Several transparent crystals of dimensions 5x5x10mm3 were obtained.3. Synthesis and preparation of AgGaS2 materialAg, Ga and S elements of 4N purity were used to grow AgGaS2 single crystals. The 1:1:2 mole ratio of Ag, Ga and S with an excess of 0.5% sulfur, as the precursor materials and 10 mgcm-3of high purity iodine as the transporting agent were taken in a quartz ampoule. In order to prevent the component deviation from stoichiometry resulting from all possible volatile loss of sulfur during initial steps, it was found necessary to add some excess sulfur. The starting materials were taken in a quartz ampoule (15 mm in diameter and 180 mm in length) evacuated to 2×10-6 torr and then sealed off. The ampoule was placed into the double zone [source and growth zones] horizontal electrical furnace. The furnace was controlled by Eurotherm temperature controller and the accuracy is ± 0.1 K. During the first stage the furnace was slowly heated up at the rate of 10 K/h. The temperatures of the source and the growth zones were allowed to reach up to 1023 and 1073 K, respectively in order to clean the wall of the ampoule. The duration was 20 h. After this, the temperature of source zone and growth zone were maintained at 1073 and 1023 K, respectively for the next 15 days. After these 15 days the furnace was slowly cooled off at a rate of 20 K/h. When the temperature of the ampoule reached the room temperature it was opened to obtain yellow colored AgGaS2 crystals. The crystals were then cleaned in an ultrasonic bath containing a mixture of acetone-methanol and then rinsed with deionized water.Similarly single crystals of AgGaS2 were grown with same iodine concentration and source zone temperature of 1073 K. The temperature differences of 100 K were maintained between source and growth zone so that, the temperature of the growth zone was maintained at 973 K. The growth was carried out for a period of 15 days. The AgGaS2single crystals obtained were yellow in color. Experimental details and the size of as-grown AgGaS2 single crystals by CVT are given in the Table 1. The AgGaS2single crystals grown at growth zone temperatures of 1023 and 973 K are shown in Figures 1a and 1b, respectively [12].Table 1. Comparison of different experimental results of as-grown AgGaS 2 single crystals by CVT method Source zone temperature (K) Growth zone temperature (K)Temperature difference (K)Crystals size (mm 3) Color of the crystals 1073 1023 50 5×5×6 and 6×4.5×5 Yellow 10739731002.5×1.5×2YellowFigure 1 a. AgGaS 2 crystals grown at 1023 K.Figure 1 b. AgGaS2 crystals grown at 973 K.4. Characterization StudiesThe powder of the YCOB crystal was analyzed by the powder X-ray diffraction studies using a Rich Seifert diffractometer with CuKa radiation source (l=1.540 ) at a scan rate of 0.051/min. The X-ray studies were carried out at room temperature. The powder XRD pattern matches well with the previously available reports. Hence, the formation of YCOB single phase is confirmed. The X-ray diffraction data of the YCOB single crystal was collected using a Enraf-Nonius CAD-4 diffractometer, with graphite monochromated CuKa radiation source. Single crystals XRD studies reveal that YCOB crystal belongs to the monoclinic system. The space group is Cm and the cell parameters are a=8.0 , b=15.9 , c=3.5 , = =90° and =101.2°. The obtained cell parameters are in good agreement with the earlier reports [9]. Transmission spectral studies are an important study for any NLO material, since an NLO material can be employed in devices only if it has a wide transparency window. To find the transmission range of the YCOB crystals, the UV–vis–NIR spectral transmittance was recorded for as-grown single crystal of YCOB of 2mm thickness in the wavelength range of 190–1100 nm. The lower cutoff wavelength for the YCOB crystal was around 220 nm. The as-grown crystal is nearly 78% transparent in the UV and visible regions. The lower cutoff value is in good agreement with the YCOB crystals grown using the Czochralski method [10]. The crystal was nearly 55% transparent in the UV and visible regions (4220 nm) when lithium carbonate was used asthe flux [8]. But the transmission percentage has increased to 78% for the crystal when the YCOB single crystals grown from borontri- oxide flux. Hence, the change in the flux has played a vital role in enhancing the optical quality of the crystals. The presence of a wide transmission in the UV and visible regions enables sufficient transmission of the higher order harmonics of Nd:YAG laser sources. The FTIR spectrum was recorded using the KBr pellet method which present investigation is in good agreement with the results obtained for other borates indicating the wavenumbers of fundamental vibrations of (BO3)3- ions in the four distinct regions 1350–1200, 950–930, 790–730 and 680–590 cm-1[11]. The absorption peaks at 1210.0 cm-1and 940.06 cm-1are due to the asymmetric and the symmetric stretching modes of (BO3)3- ions. The absorption peaks at 740.25 and 617.27 cm-1 are due to the symmetric and asymmetric bending modes of (BO3)3- ions. The absorption peak at 515.30 cm-1 is due to the internal vibration of Ca–O bond. The vibration due to the yttrium and oxygen atom which is not bonded with (BO3)3- ions is indicated by the peak at 452.9 cm-1. All possible peaks of the YCOB crystal are present in the FTIR spectrum.5. ConclusionPolycrystalline YCOB powder was synthesized by the solid state reaction method. The growth of YCOB single crystals from the boron-tri-oxide flux was carried out for the first time. The grown crystals were subjected to various characterization studies to confirm the formation of YCOB single phase. The lattice parameters of the YCOB crystals were calculated from the single crystal XRD analysis. The as-grown YCOB crystal is highly transparent in the visible and UV regions (4220 nm). This makes the crystal more suitable for device applications. The FTIR analysis confirms the presence of all the functional groups in the grown YCOB single crystal. The results obtained indicate that the flux technique is a best alternate method to melt technique for the growth of YCOB single crystals with high optical quality. Stoichiometric AgGaS2 single crystals were grown by CVT method. 50 K temperature difference between the source and growth zones yielded big size AgGaS2 single crystals when compared to the crystals grown with temperature difference of 100 K. The powder XRD and X-ray rocking curves studies revealed the desired phase formation of AgGaS2and good crystalline perfection of the grown crystal without any structural grain boundaries respectively. Therefore, the quality of the crystals obtained in the present investigations was found to be good. Single crystal XRD studies of AgGaS2single crystals grown at different growth zone temperatures confirmed the chalcopyrite structure. From optical transmittance spectra, 60 % transmittance was observed of as-grown AgGaS2 single crystals. PL spectra of as-grown AgGaS2 single crystals show prominent band edge emission at 2.61 eV. DTA curve indicates a sharp endothermic peak at 995.4˚C. The results obtained from the resistivity measurement shows that as-grown AgGaS2 single crystals were of semi-insulating nature.References[1]Vivien D, Aka G, Kahn-Harari A, Aron A, Mougel F, Benitez J M, Ferrand B, Klein R, KugelG, Nain N L and Jacquet M 2002 J. Crystal Growth237-239 621-28.[2]Sasaki T, Mori Y, Yoshimura M, Yap Y K and Kamimura T 2000 Mater. Sci. Eng. 30 1-54.[3]Luo J, Fan S, Wang J, Zhong Z, Qian G and Sun R 2001 J. Crystal Growth229 261-64.[4]Li L X, Guo M, Jiang H D, Hu X B, Shao Z S, Wang J Y, Wei J Q, Xia H R, Liu Y G andJiang M H 2000 Cryst. Res. 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