Transparent Crystals Research Articles

Mechanically exfoliated low-layered [Ca2CoO3]0.62[CoO2]: A single-crystalline p-type transparent conducting oxide

Transparent conducting oxides (TCOs) are essential components of optoelectronic devices and various materials have been explored for highly efficient TCOs having a combination of high transmittance and low sheet resistance. Here, we focus on a misfit thermoelectric oxide [Ca2CoO3]0.62[CoO2] and fabricate the transparent low-layered crystals by a mechanical tape-peeling method using the single-crystalline samples. From the transmittance measurement, we find that the thickness of low-layered samples is several orders of hundred nanometers, which is comparable with the estimation from the scanning electron microscopy images. Compared to the previous results on the polycrystalline and c-axis oriented transparent films, the electrical resistivity is reduced owing to the single-crystalline nature. The figure of merit for the transparent conducting materials in the present low-layered samples is then evaluated to be higher than the values in the previous reports. The present results on the low-layered single-crystalline [Ca2CoO3]0.62[CoO2] may offer a unique class of multi-functional transparent thermoelectric oxides.

Structural, raman, optical and electrical studies of pure and compound crystal of magnesium sulphateheptahydrate and threonine

Pure and compound crystal of magnesium sulphate heptahydrate(MSH) and threonine (THR) is grown from aqueous solution by slow evaporation method at room temperature. The reaction between MSH and THR is confirmed by TLC test. Good quality and transparent crystals are harvested. Pure MSH and THR crystallize in orthorhombic crystal system, while compound crystal shows the presence of both the phases of MSH and THR.The crystallite size is found using the various methods are employed to estimate the crystallite sizes and the lattice strain. The Raman spectra show the presence of characteristic normal modes of vibrations of pure MSH and THR in the compound crystal.The optical band gap is estimated by using K-M function. The various optical parameters such as extinction coefficient, refractive index, optical conductivity and skin depth have been calculated and analyzed with incident photon energy. The dielectric constant and loss of all the grown crystals have exhibited normal behavior over the frequency range considered. The total polarizability of the crystals is calculated by two theoretically methods and matches well with experimental results. The complex impedance and modulus spectroscopy studies suggested the presence of grain effect in all the samples and the same is successfully modelled using R-CPE parallel circuit. Non-debye type relaxation is confirmed from β-parameter. From the Jonscher’s plot, the ideal long range pathways and diffusion limited hopping mechanism is confirmed for all the samples. The results of pure crystal of MSH and THR are compared with the compound crystal and discussed accordingly in detail.

Crystal growth, structural insights, spectral, Z-scan, N[sbnd]H…O hydrogen bonding interaction and non-linear optical properties of the novelly synthesized 2-aminopyridinium cyanoacetate crystal

A novel organic single crystal 2-aminopyridinium cyanoacetate (2ACY) was synthesized and analysed by using UV–Vis, FT-IR, FT-Raman and single crystal X-ray diffraction experiments. Optically transparent and defect free crystal was grown from aqueous solution by slow evaporation technique at room temperature. All theoretical computations were carried out using the density functional theory (DFT) B3LYP approach using the basis set of 6–31+G(D). The grown crystal exhibits good optical transmittance in the UV–visible spectral analysis. The thermal behaviour of the 2ACY crystal has been analysed by TG/DTA analysis. Besides, the intermolecular interactions have been inquired and revealed by NBO analysis. Intermolecular contacts and molecular surface contours were analysed by using Hirshfeld and 2D fingerprint plot analysis. Topological analysis of electron localization function (ELF), localized orbital locator (LOL) and reduced density gradient(RDG) were evaluated. Additionally molecular electrostatic potential (MEP), HOMO-LUMO and charge analysis of the title compound have been investigated. The fluorescence behaviour of 2ACY crystal has been analysed in visible region and red colour emission is evidenced at 610 nm. The outcome of SXRD, UV-visible, TG/DTA, NLO, LDT and Z-scan values were compared with earlier reported compounds and amongst which the analysed compound 2ACY show good NLO activity. The occurrence of protonated intermolecular NH…O hydrogen bonding interaction liable for the nonlinear optical activity and it was projected using theoretical along with experimental techniques.

Quantification of polarization distribution from polarizing light microscopy images of ferroelectric single crystals

Qualification of polarization can be realized either on a macroscopic scale as an average property by P-E hysteresis measurements or on a nano/micro scale by piezoelectric force microscopy, transmission electron microscopy, scanning electron microscopy, and so on. However, visualization and qualification of polarization distribution in the micron to millimeter scale is still a challenge. Polarizing light microscopy (PLM) is often used in the study of ferroelectric domain structures mainly for domain patterns. A phenomenon called “chromatic polarization” has been observed in transparent ferroelectric crystals by using a crossed-PLM system viewed with white light, which contains rich information about local polarization distribution. In this study, an automatic full-angle light intensity detection (AFALID) algorithm combined with colorimetry is developed to analyze the distribution of nonuniform local spontaneous polarization distribution in transparent ferroelectric single crystals. Temperature-dependent spontaneous polarizations from the color analysis for PMN-0.36PT single crystals with single tetragonal domain state are in good coincidence with those extracted from temperature-dependent hysteresis loops and pyroelectric current measurements. We further apply this method to quantify the nonuniform domain distributions with nano-indentations. This non-contact and non-destructive characterization can provide fast and automatic detection of polarization distributions in ferroelectric materials.

Ultralong afterglow and unity quantum yield from a transparent CsCdCl3:Mn crystal

AbstractTransparent afterglow crystals are keenly desired for three‐dimensional information storage. Herein, CsCdCl3 perovskite crystals were grown by a programmable cooling procedure in a hydrothermal reactor. The pristine crystal showed an abnormal optical behavior where the absorption increased by 2.3 folds at high temperature, leading to a fourfold boost of photoluminescence (PL) intensity. After Mn2+ doping, the PL quantum yield was improved to nearly unity. Importantly, the doped crystals exhibited an ultralong afterglow up to 12 h after ceasing UV excitation and a high transmittance up to 75% in the visible region. This work brought a new member to the library of transparent afterglow crystal, opening up many possibilities to advanced applications such as volumetric display and three‐dimensional information encryption.

Graphene Oxide Based Transparent Resins For Accurate 3D Printing of Conductive Materials

AbstractDigital Light Processing (DLP) allows the fast realization of 3D objects with high spatial resolution. However, DLP is limited to transparent resins, and therefore not well suited for printing electrically conductive materials. Manufacturing conductive materials will significantly broaden the spectrum of applications of the DLP technology. But conductive metals or carbon‐based fillers absorb and scatter light; inhibiting thereby photopolymerization, and lowering resolution. In this study, UV transparent liquid crystal graphene oxide (GO) is used as precursor for generating in situ conductive particles. The GO materials are added to a photopolymerizable resin via an original solvent exchange process. By contrast to earlier contributions, the absence of drying during the all process allows the GO material to be transferred as monolayers to limit UV scattering. The absence of UV scattering and absorption allows for fast and high‐resolution 3D printing. The chosen resin sustain high temperature to enable an in situ efficient thermal reduction of GO into reduced graphene oxide (rGO) that is electrically conductive. The rGO particles form percolated networks with conductivities up to 1.2 × 10−2 S m−1. The present method appears therefore as a way to reconcile the DLP technology with the manufacturing of 3D electrically conductive objects.

REACTIONS OF ALKYLTRIPHENYLPHOSPHONIUM HALIDES WITH ARENESULFONIC ACID

The reaction of equimolar amounts of alkyltriphenylphosphonium bromides with 1-naphthalenesulfonic, 2,4-dinitrobenzenesulfonic, and sulfosalicylic acids in water leads to the formation of ionic alkyltriphenylphosphonium arenesulfonates [Ph3PR][OSO2Ar], R = CH2OMe, Ar = Naft-1 (I); R = CH=СHPPh3, Ar = C6H3(NO2)2-2,4 (II); R = (CH2)2Br (III), R = C6H11-cyclo (IV), Ar = C6H3(COOH-3)(OH-4). Structures of complexes I‒IV have been established by X-ray diffraction analysis. Complexes I–IV are air-stable transparent crystals, readily soluble in arenes, ethanol, chloroform, acetonitrile, tetrahydrofuran, carbon tetrachloride, diethyl ether, and poorly soluble in water at room temperature. Phosphorus atoms in alkyltriphenylphosphonium cations I–IV have tetrahedral coordination, arenesulfonate anions have the usual geometry with a tetrahedral sulfur atom. Compound II crystallizes as a hydrate. The P–C bond lengths vary in the range 1.240(3)–1.827(3) Å, which is less than the sum of the covalent radii of partner atoms (1.83 Å). CPC bond angles vary within 103.77(9)°−112.80(12)°; S–C distances in sulfonate anions are 1.768(3)‒1.807(3) Å. The S–O bond lengths are close to each other and take the values 1.427(3)‒1.4710(17) Å. The bond angles OSO (111.56(10)°−115.74(18)°) are larger than the OSC angles (103.02(12)°−107.26(9)°). Cations and anions in complexes I‒IV are connected by short contacts of S=O∙∙∙Н(Рh) type [2.350‒2.717 Å] (the sum of Van der Waals partner atoms O···Н is 2.62 Å). In crystal II, short contacts of the N=O∙∙∙H(Ph) type [2.448–2.699 Å] are also observed. Crystal structures of I, III, IV contain CH∙∙∙π interactions (2.658‒2.898 Å). Moreover, the spatial structure of crystals II, III is formed with the participation of π–π interactions. (3.276‒3.359 Å). For citation: Sharutin V.V., Sharutina O.K., Mekhanoshina E.S. Reactions of alkyltriphenylphosphonium halides with arenesulfonic acid. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 18-26. DOI: 10.6060/ivkkt.20236603.6724.

Tin Bromido Aluminate Networks with Bright Luminescence.

The novel tin bromido aluminates [Sn3 (AlBr4 )6 ](Al2 Br6 ) (1), Sn(AlBr4 )2 (2), [EMIm][Sn(AlBr4 )3 ] (3) and [BMPyr][Sn(AlBr4 )3 ] (4) ([EMIm]: 1-ethyl-3-methylimidazolium, [BMPyr]: 1-butyl-1-methyl-pyrrolidinium), are obtained from a ionic-liquid-based reaction of AlBr3 and SnCl2 or SnBr2 , resulting in colorless and transparent crystals. 1 contains a neutral, inorganic ∞ 3 [Sn3 (AlBr4 )6 ] network filled with intercalated Al2 Br6 molecules. 2 represents a 3D structure isotypic to Pb(AlCl4 )2 or α-Sr[GaCl4 ]2 . 3 and 4 exhibit infinite ∞ 1 [Sn(AlBr4 )3 ]n- chains that are separated by the voluminous [EMIm]+ /[BMPyr]+ cations. All title compounds contain Sn2+ coordinated by AlBr4 tetrahedra, resulting in chains or 3D networks. Moreover, all title compounds show photoluminescence due to Br- →Al3+ ligand-to-metal charge-transfer excitation, followed by 5s2 p0 ←5s1 p1 emission on Sn2+ . Most surprisingly, the luminescence is highly efficient (quantum yield >50 %). Specifically, 3 and 4 exhibit outstanding quantum yields of 98 and 99 %, which are the highest values observed for Sn2+ -based luminescence so far. The title compounds have been characterized by single-crystal structure analysis, elemental analysis, energy-dispersive X-ray analysis, thermogravimetry, infrared and Raman spectroscopy, UV-Vis and photoluminescence spectroscopy.

Generation of 2 μm few-cycle laser pulse with dual laser filaments nonlinear processes

For the first time, we propose a new scheme for generating few-cycle 2 μm seed laser pulse in an optical parametric chirped pulse amplifier (OPCPA) front-end. The 2 μm ultrafast seed laser pulse is generated via a difference frequency generation (DFG) process between the visible and near-IR supercontinuum from two different filamentation processes inside the transparent YAG crystals. The generated DFG pulse spectrum has a broad spectrum range of 1200 nm from 1500 nm to 2700 nm. By further scaling up the pulse energy of the seed laser pulse via a non-collinear optical parametric amplification (OPA) stage, the single pulse energy is boosted to 15.6 μJ. After dispersion compensation, the pulse duration is compressed to 14.3 fs with its spectrum covering from 1600 nm to 2600 nm.

Growing solid deuterium for UCN production

We have experimentally studied growing a large (about 1 liter) ortho-deuterium crystal in a real UCN source cryostat and recorded the growing process optically using a camera. The best quality was observed when growing the crystal directly from a vapor phase. The crystal was grown at different mass flows of deuterium and annealed at different temperatures. Optimum conditions were found for both, obtaining an optically transparent crystal and cooling it down with minimal damage. We found that the quality, final shape and changes during annealing of the crystal are very much dependent on the temperature profile of the cryostat walls.

James E. Talmage and the Selenite Crystals

James E. Talmage and the Selenite Crystals

New Minerals from the Redmond Mine, North Carolina, USA: I. Redmondite, Hydroredmondite, and Sulfatoredmondite, Three Minerals Containing the Novel [Pb8O2Zn(OH)6]8+ Structural Unit

AbstractThe new minerals redmondite (IMA2021–072), [Pb8O2Zn(OH)6](S2O3)4, hydroredmondite (IMA2021–073), [Pb8O2Zn(OH)6](S2O3)4·2H2O, and sulfatoredmondite (IMA2021–089), [Pb8O2Zn(OH)6](SO4)4·6H2O, were found in the Redmond mine, Haywood County, North Carolina, USA, where they occur together in a highly unusual secondary assemblage that comprises a variety of rare Pb-Zn-Cu sulfates, thiosulfates, and carbonates. The properties of redmondite are as follows: colorless to shades of brown, transparent equant rhombs to about 1 mm; white streak; adamantine luster; brittle; Mohs hardness 2; conchoidal fracture; no cleavage; 5.757 g/cm3 calculated density; biaxial with α = 1.96–1.97, β = 1.97–1.98, γ = 1.97–1.98; extreme dispersion. The properties of hydroredmondite are as follows: colorless, transparent prisms, blades, and tablets up to about 1 mm; white streak; adamantine luster; brittle; Mohs hardness 2; curved and stepped fracture; good cleavages on {101} and ; 5.124 g/cm3 calculated density; biaxial (+) with α = 1.830(5), β = 1.880(calc), γ = 1.950(calc), 2Vmeas = 83(1)°. The properties of sulfatoredmondite are as follows: colorless, transparent wedge-shaped crystals to about 2 mm; white streak; adamantine luster; brittle; Mohs hardness 2; curved, irregular fracture; no cleavage; 5.173 g/cm3 calculated density; biaxial (+), α = 1.780(5), β = 1.850(calc), γ = 1.860(calc), 2Vmeas = 40(3)°; moderate r > v dispersion. Electron probe microanalyses provided the empirical formulae: Pb8.16Zn1.00S6+3.97S2−3.97O20H5.79, Pb8.00Zn1.00S6+4.00S2−4.00O22H9.98, and Pb8.00Zn0.99S6+4.00S2−0.89O29.11H17.98 for redmondite, hydroredmondite, and sulfatoredmondite, respectively. Redmondite is monoclinic, P21/c, a = 9.1672(4), b = 10.6576(4), c = 14.0620(10) Å, β = 101.173(7)°, V = 1347.83(12) Å3, and Z = 2. Hydroredmondite is monoclinic, P21/n, a = 12.5991(9), b = 9.2819(4), c = 12.9774(9) Å, β = 90.443(6)°, V = 1517.57(16) Å3, and Z = 2. Sulfatoredmondite is monoclinic, C2/m, a = 17.294(2), b = 7.3668(9), c = 12.7271(18) Å, β = 110.622(9)°, V = 1517.5(4) Å3, and Z = 2. The crystal structures of redmondite (R1 = 0.0346 for 2061 I > 2σI), hydroredmondite (R1 = 0.0346 for 3022 I > 2σI), and sulfatoredmondite (R1 = 0.0344 for 1661 I > 2σI) are all based on the same [Pb8O2Zn(OH)6]8+ structural unit.

Studies on synthesis, structural, thermal, optical, spectral and mechanical properties of an inorganic strontium nitrate NLO single crystal

An inorganic NLO single crystal of strontium nitrate (SrN) was successfully grown from an aqueous solution, by slow evaporation technique at ambient temperature. Good transparent SrN crystals were obtained within 2 weeks. Various characterizations were carried out to ensure the application of the grown material. Single crystal XRD study reveals that the crystal shows a cubic structure with a centrosymmetric Pa3¯ space group. The crystalline nature of the compound was confirmed by powder X-ray diffraction. The unit cell dimension of the SrN crystal was found to be, a=b=c=7.8220 Å, and the axial angle is α =β=γ=90°. The average crystalline size of the material was 52 nm. The various functional groups associated with grown crystals have been characterized by FTIR and FT-Raman spectroscopy studies. The lower cut-off wavelength is found to be 320 nm and the band gap energy of the SrN crystal was 3.9 eV. The synthesized crystal exhibits 84% transmittance in the visible region. The grown crystals were thermally stable up to 135 °C. Various mechanical parameters such as microhardness (Hv), work hardening coefficient (n), elastic stiffness (C11), and yield strength (σy) of the grown material have been carried out by the indentation method. The nonlinear refractive index (n2), nonlinear absorption coefficient (β), and third order nonlinear susceptibility (χ(3)) were studied using the Z-scan technique, which involves open and closed aperture measurements with a continuous wave laser of 632.8 nm.

Investigating the structure and optical characteristics of two new organic-inorganic hybrid crystals

Using the solvent evaporation approach at room temperature (RT), we produced transparent single crystals of two new organic-inorganic hybrid materials: (C5H6NO)SO3NH2 (crystal 1: reaction by sulfamate and 4-hydroxypyridine) and (C3H5N2)SO3NH2 (crystal 2: reaction by sulfamate and imidazole). Both crystals have the same space structure and belong to the P21/c space group of the monoclinic crystal system, according to the results of X-ray single crystal diffraction. In crystals 1 and 2, sulfamic acid and organics (4-hydroxypyridine, imidazole) are alternatively positioned by hydrogen bonds to create a layered structure. Hydrogen bonds and electrostatic Coulomb forces connect the layers to one another. Powder XRD demonstrates the remarkable phase purity of both crystals. Furthermore, the optical properties of both crystals, including IR, UV absorption, and fluorescence spectra, have been investigated in detail. The presence of functional groups such as NH2 and CC in the grown crystals was confirmed by Fourier transform infrared analysis. The optical band gaps for crystals 1 and 2 are about 4.33 and 4.31 eV, respectively, and the UV absorption findings show a low light absorption. According to the photoluminescence spectra, the two crystals have distinct fluorescence characteristics, with emission peaks of approximately 433 nm and 442 nm, apiece.

Analytical and numerical modeling of optical second harmonic generation in anisotropic crystals using ♯SHAARP package

Electric-dipole optical second harmonic generation (SHG) is a second-order nonlinear process that is widely used as a sensitive probe to detect broken inversion symmetry and local polar order. Analytical modeling of the SHG polarimetry of a nonlinear optical material is essential to extract its point group symmetry and the absolute nonlinear susceptibilities. Current literature on SHG analysis involves numerous approximations and a wide range of (in)accuracies. We have developed an open-source package called the Second Harmonic Analysis of Anisotropic Rotational Polarimetry (♯SHAARP.si) which derives analytical and numerical solutions of reflection SHG polarimetry from a single interface (.si) for bulk homogeneous crystals with arbitrary symmetry group, arbitrary crystal orientation, complex and anisotropic linear dielectric tensor with frequency dispersion, a general SHG tensor and arbitrary light polarization. ♯SHAARP.si enables accurate modeling of polarimetry measurements in reflection geometry from highly absorbing crystals or wedge-shaped transparent crystals. The package is extendable to multiple interfaces.

Ce concentration dependence on scintillation properties of SrHfO3 single crystals

Transparent and yellowish Ce-doped SrHfO3 (Ce:SHO) single crystals were grown by the xenon lamp equipped floating zone method. The synthesized crystals were in the single phase of SHO crystal structure, and no impurity phases such as HfO2 were evident by the X-ray diffraction analysis. The Ce:SHO shows blue luminescence peaking at 410 nm in both the PL and scintillation spectra, and the decay time constant was approximately 14 ns. The PL QY increases with the Ce concentration, which was confirmed up to 5%. The afterglow level is the lowest when the Ce concentration is 3%. The full energy peak can be demonstrated with all the Ce:SHO single crystals prepared in this study under 241Am alpha-ray irradiation, and the estimated light yield is 396 photons/MeV for the 3% Ce:SHO, which is the highest among the samples studied.

Visualization of transparent particles based on optical spatial differentiation.

Optical analog computing operates on the amplitude, phase, polarization, and frequency distributions of the electromagnetic field through the interaction of light and matter. The differentiation operation is widely used in all-optical image processing technology, such as edge detection. Here, we propose a concise way to observe transparent particles, incorporating the optical differential operation that occurs on a single particle. The particle's scattering and cross-polarization components combine into our differentiator. We achieve high-contrast optical images of transparent liquid crystal molecules. The visualization of aleurone grains (the structures that store protein particles in plant cells) in maize seed was experimentally demonstrated with a broadband incoherent light source. Avoiding the interference of stains, our designed method provides the possibility to observe protein particles directly in complex biological tissues.

Fluorescence Monitoring Oxidation of Extra Virgin Olive Oil Packed in Different Containers.

'Picual' olive oil was stored in different types of containers for 10 months and monitored via quality parameters. In combination with the mentioned analysis, non-destructive fluorescence spectroscopy was performed combined with multivariate analysis to monitor and quantify oil quality levels. Excitation emission matrices (EMMs) were analyzed using parallel factor analysis (PARAFAC). According to the quality parameters, it was observed that Transparent Crystal (TC) and Opaque Crystal (OC) samples were the ones that deteriorated faster due to their higher exposure to light in comparison with Plastic (P) and Canned (C) samples. In a fast and non-destructive manner, the fluorescence spectroscopy-based prototype successfully monitored the oxidation changes in the EVOOs. Unfolded partial least squares (U-PLS) was used to generate a regression model to quantify quality parameters. Good correlation coefficients were found for the peroxide index, K232 and the oxidative stability index (r2 between 0.90 and 0.94 for cross-validation and validation). For all of that, the results obtained confirmed the ability of fluorescence spectroscopy to monitor the quality of olive oil and EEMs combined with U-PLS can be used to analyze these parameters, eluding the classical methods.

Preparation of Large Volume Solid Argon Crystal and Its Feasibility Test as a Scintillation Material

An important background to the liquid argon detectors is that they are caused by the diffusion of radioactive isotopes in a scintillator (liquid phase). This radioactive isotope is produced in argon’s surrounding devices, such as circulation pipelines and liquid argon containers. The solid argon as a scintillation material in the detector can inhibit the diffusion and drift of radioactive isotopes in a solid phase scintillator. Additionally, the structure of a solid argon detector is simple and reduces the total source of radioactive background. In the CDEX-300 detection system, solid argon could substitute for liquid argon as the veto detector, preventing radioactive isotopes drifting to the central main detector (HPGe detectors array) surface to reduce backgrounds. Therefore, solid argon has great potential in the experiments since it is especially helpful to get the lower background in a larger active volume than liquid argon required in those low background detection experiments. This work introduces the preparation process and device of the large volume transparent crystalline argon, the acquisition of scintillation light, and the pulse amplitude spectrum of 137Cs obtained from a prototype detector of transparent solid argon crystal. The results show that the scheme proposed in this study can successfully produce a large volume transparent crystalline argon detector, the scintillation light signals can be effectively obtained from the solid argon scintillator, and the corresponding pulse amplitude spectrum is given. This work indicates that it is feasible to develop a solid argon crystal scintillation detector by using our approach.

Effect of shock wave on surface morphology and optical properties of acid phthalate based single crystals

Recent literature reports mentioned that the effect of shock wave on single crystals and its effect on various physical and chemical properties. In the current article, the shock wave with constant Mach number 1.7 was generated by table top shock tube to study its effects on optical and surface morphology properties of Potassium Acid Phthalate (KAP) and Sodium Acid Phthalate (NaAP) single crystals respectively. Optically transparent semi-organic single crystals of KAP and NaAP were grown using slow evaporation solution technique (SEST). A systematic investigation was carried out to examine the influence of shock waves on acid phthalate based single crystals. The optical properties of harvested crystals were scrutinized using UV–Visible and photoluminescence (PL) spectroscopy. The surface morphology analysis was examined by optical microscope. On the interaction of shock wave, the transmittance for both the crystals increased for 1st shock wave and then decreased for its higher shock numbers. There were no major changes observed in optical band gap for pre and post shock wave loaded single crystals. The modification on the surface of single crystal, study of defects concentration and crystalline perfection of the virgin and shock wave loaded samples were confirmed by PL and surface morphology studies respectively.