Temperature and excitation intensity tuned photoluminescence in Tl4GaIn3S8 layered single crystals

Photoluminescence spectra of Tl₄GaIn₃S₈ layered crystals grown by Bridgman method have been studied in the wavelength region of 500–780 nm and in the temperature range of 26–130 K with extrinsic excitation source (λ_exc = 532 nm), and at T = 26 K with intrinsic excitation source (λ_exc = 406 nm). Three emission bands A, B and C centered at 514 nm (2.41 eV), 588 nm (2.11 eV) and 686 nm (1.81 eV), respectively, were observed for extrinsic excitation process. Variations in emission spectra have been studied as a function of excitation laser intensity in the 0.9‐183.0 mW cm^–2 range for extrinsic excitation at T = 26 and 50 K. Radiative transitions from the donor levels located at 0.03 and 0.01 eV below the bottom of the conduction band to the acceptor levels located at 0.81 and 0.19 eV above the top of the valence band were proposed to be responsible for the observed A‐ and C‐bands. The anomalous temperature dependence of the B‐band peak energy was explained by configurational coordinate model. From X‐ray powder diffraction and energy dispersive spectroscopic analysis, the monoclinic unit cell parameters and compositional parameters of Tl₄GaIn₃S₈ crystals were determined, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared photoluminescence from TlGaS2 layered single crystals

Photolimuniscence (PL) spectra of TlGaS₂ layered crystals were studied in the wavelength region 500‐1400 nm and in the temperature range 15‐115 K. We observed three broad bands centered at 568 nm (A‐band), 718 nm (B‐band) and 1102 nm (C‐band) in the PL spectrum. The observed bands have half‐widths of 0.221, 0.258 and 0.067 eV for A‐, B‐, and C‐bands, respectively. The increase of the emission band half‐width, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature are explained using the configuration coordinate model. We have also studied the variations of emission band intensity versus excitation laser intensity in the range from 0.4 to 19.5 W cm^‐2. The proposed energy‐level diagram allows us to interpret the recombination processes in TlGaS₂ crystals. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence Spectra of GaS0.75Se0.25 Layered Single Crystals

Photoluminescence (PL) spectra of GaS_0.75Se_0.25 layered single crystals have been studied in the wavelength region of 500‐850 nm and in the temperature range of 10‐200 K. Two PL bands centered at 527 ( 2.353 eV, A‐band) and 658 nm (1.884 eV, B‐band) were observed at T = 10 K. Variations of both bands have been studied as a function of excitation laser intensity in the range from 8 × 10^‐3 to 10.7 W cm^‐2. These bands are attributed to recombination of charge carriers through donor‐acceptor pairs located in the band gap. Radiative transitions from shallow donor levels located 0.043 and 0.064 eV below the bottom of conduction band to acceptor levels located 0.088 and 0.536 eV above the top of the valence band are suggested to be responsible for the observed A‐ and B‐bands in the PL spectra, respectively.     

Growth and characterization of photorefractive Bi12TiO20 single crystals

Photorefractive Bi₁₂TiO₂₀ single crystals of high optical quality were grown in a resistive heating furnace from high temperature nonstoichiometric (10:1) solutions of Bi₂O₃ and TiO₂ at pulling rates 0.3–0.8 mm/h at rotation 20–30 rpm along the <001> and <011> axis. Powder X-ray analysis, Laue method, and electron-probe microanalysis were used for characterization. BTO crystals have the bcc structure of sillenite type with a₀ = 10.178(8) Å. The chemical composition of the crystals can be written down as Bi_{12.1 ± 0.2}Tio_{0.96 ± 0.09}O_20.1. Natural optical activity ρ of BTO crystals is 6.3 ± 0.2 deg/mm at λ = 0.633 μm and 11.9 ± 0.2 deg/mm at λ = 0.5145 μm, optical absorption coefficient α = 0.42 ± 0.04 cm⁻¹ at λ = 0.633 μm and linear electro-optic coefficient r₄₁ = r₅₂ = r₆₃ = 5.3 pm/V. Fanning effect in the “fiber-like” BTO sample was studied and double phase conjugation with conversion efficiency up to 8% was observed in a wide range of incidence angles of the pump at λ = 0.633 μm for 2 × 3 mW input light power.     

Luminescence of crystals of divalent tungstates

Crystals of divalent tungstates are characterized by two main luminescence spectral ranges: a short-wavelength (blue) luminescence band in the range 390–420 nm and a group (often two groups) of longer wavelength (green) bands in the range 480–520 nm. For crystals of calcium, strontium, barium, cadmium, magnesium, zinc, and lead tungstates, it is shown that the wavelength corresponding to the maximum of the blue luminescence band (λ_max) correlates with the melting temperature (T_m) of these compounds. The position of the blue luminescence band is the same (in the range 510–530 nm) for crystals with different divalent cations. Annealing in vacuum and electron irradiation decrease the intensity of both blue and green luminescence bands but do not change the ratio of their maximum intensities. This circumstance suggests that vacancies serve as luminescence quenchers to a greater extent rather than facilitate the formation of emission centers responsible for a particular luminescence band.     

Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1‐x) mixed crystals (0.25 ≤ x ≤ 1)

The optical properties of the TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400–1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS_2xSe_2(1‐x)mixed crystals. The transmission measurements carried out in the temperature range of 10–300 K revealed that the rates of change of the indirect band gaps with temperature are γ = –9.2×10^–4 eV/K, –6.1×10^–4 eV/K, –4.7×10^–4 eV/K and –5.6×10^–4 eV/K for TlInS₂, TlInS_1.5Se_0.5, TlInSSe and TlInS_0.5Se_1.5 crystals, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of doping on OH absorption in LiNbO3 crystals

Undoped, Cr doped and Mg, Cr codoped LiNbO₃ crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV‐Visible spectroscopy. Infrared optical absorption for OH^– ion has been used to study the effect of dopants on the crystals. The peak position of OH^– shift to 3535 cm^‐1 for Mg, Cr codoped crystals compared to 3484 cm^‐1 for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm^‐1) and 653 nm (15313 cm^‐1) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm^‐1) and 678 nm (14749 cm^‐1). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO₃ crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear Optical Properties of Isomorphic Family of Crystals with Yttrium-Aluminium Borate (YAB) Structure

The second harmonics generation of Nd-laser radiation (λ = 1.06 microns) of the isomorphic family of crystals with yttrium-aluminium borate (YAB) structure — RAl₃(BO₃)₄ (R = Y, Sm, Eu, Gd, Dy, Er, Ho, Tu) — investigated using the powder method and the theoretical calculation of SHG–coefficients — are reported. The refraction indices (for λ = 5481 Å) and optical sign for all studied YAB-type crystals are determined with the help of the immersion method. All studied crystals possess PM direction and oee-interaction. The SH-intensity is of KDP order of magnitude, with reasonable correlation of experimental and theoretical data. Theoretical analysis of the contributions of different ions to the integral d magnitude has shown identical signs for all ion species in YAB structure type.     

Temperature‐tuned band gap energy and oscillator parameters of Tl2InGaSe4 semiconducting layered single crystals

The optical properties of Tl₂InGaSe₄ layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10^‐4 eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10^–7 m and 9.64 × 10¹³ m^–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Luminescence characteristics of undoped and Eu‐doped GdCa4O(BO3)3 single crystals and nanopowders

Single crystals of GdCa₄O(BO₃)₃ (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling‐down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu³⁺ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu²⁺ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol‐gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd³⁺ at about 312 nm, whereas this emission dramatically decreases in Eu‐doped crystals upon X‐ray excitation, as well as in Eu‐doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125‐333 nm for Eu‐doped samples leads to strong emission in red coming from the ⁵D₀ multiplet of Eu³⁺, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu‐doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd^{3+ 6}P_7/2 multiplet is 2.79 ms. The Eu^{3+ 5}D₀ decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu³⁺ luminescence in the 160‐200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd³⁺–O^2– charge transfer was not observed in crystal obtained by the micropulling‐down method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of optical parameters of Ga0.75In0.25Se layered crystals

The optical properties of the Ga_0.75In_0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380–1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10–300 K. The rate of change of band gap energy (γ = –6.2 × 10^–4 eV/K) and absolute zero value of the band gap (E_gi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index values. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and magneto-optical properties of Na0.37Tb0.63F2.26 cubic single crystal

Crystals of Na_0.37Tb_0.63F_2.26 solid solution with a fluorite structure have been grown from melt by the Bridgman technique. The measured values of the Verdet constant are V = 0.35 ± 0.02 and 0.105 ± 0.01 arcmin/(Oe cm) for λ = 633 and 1060 nm, respectively. The dispersion of the Verdet constant is studied in the range of 380–1060 nm. The Na_0.37Tb_0.63F_2.26 crystal is somewhat inferior to the previously studied noncubic fluoride crystals containing Tb³⁺ ions yields by V(λ) and is close to KTb₃F₁₀ crystal in totality of properties.     

Effect of Flux on thermoluminescence in Flux-grown BaFCl crystals

BaFCl crystals have been grown using BaF₂ and BaCl₂ by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF₂ flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.     

坩埚下降法生长CaF2单晶的研究

采用坩埚下降法生长了CaF2单晶体,研究了不同条件生长的单晶缺陷和光谱性能.结果表明:当晶体生长过程中进入水等含氧杂质时,所生长的晶体不仅在1500nm附近产生非常宽的OH-两倍振动吸收带,而且在可见-紫外波段也形成强烈的色心吸收带.同时,杂质离子Ce3+的存在也导致晶体出现306nm的吸收带.     

Photoluminescence from deformed CaO crystals

The plastic deformation of CaO crystals produces the increase of luminescence band centered at 385 nm and 454 nm. The bands are excited with light of 350 nm and 275 nm respectively, and their relative increase depends on the kind of deformation applied to the crystal. The results are compared with previous cathodoluminescence observations.     

InSeI单晶的制备及其结构与性能研究

利用化学气相传输法(CVT)制备了InSeI单晶。该晶体为黄色的针状物,晶体较脆。在室温下进行X射线衍射分析发现,其属于四方晶系,晶胞参数为a=b=1.864 3(5) nm,c=1.012 0(3) nm,V=3.517 2 nm³,空间群为I4₁/a。紫外可见光吸收光谱、光致发光光谱等结果显示该晶体的禁带宽度是2.48 eV,在一定波段光的激发下,InSeI单晶在600 nm左右有较宽的发射峰,表明该晶体的发光方式为缺陷态发光。介电温谱表明InSeI单晶在440 K时其四方相的结构发生了相变。     

Structure and optical properties of multilayer X-ray mirrors for long wave part (3.1–4.4 nm) of “water window”

Structure and optical properties (at λ - 0.154 nm and λ - 3.16 nm) of W Ti, W TiN, W Sc, and Cr Sc multilayer X-ray mirrors for long wave part of “water window”' wavelength range (3.1–4.4 nm) were studied by methods of X-ray diffractometry and cross-sectional electron microscopy. The reflectivities at λ - 0.154 nm are increased going from W TiN, Cr Sc, W Ti to W Sc multilayers. Cr Sc mirrors have highest reflectivity and resolution at λ - 3.16 nm. Influence of the ambient atmosphere on optical properties of multilayer mirrors is shown.     

Growth of large KDP single crystals for UV spectrum range

The influence of various technological parameters of crystallization (acidity of growth solutions, crystallization temperature, growth rate, degree of solution purification) on the optical absorption of large KDP single crystals has been studied in the UV range of the spectrum. It is shown that the method of solvent recirculation with the use of the starting material with the microimpurity content not exceeding 5 × 10^?5 wt % and solution ultrafiltration under the optimum crystallization conditions (t_cr = 80°C, V_cr ～ (0.8–1.6) × 10^?6 cm/s, pH 4) enables one to grow KDP single crystals with cross sections up to 300 × 300 mm² and the transmission in the vicinity of the fundamental absorption edge λ = 200 nm) equal to 86%.     

EPR and Optical Absorption Studies of Radiation-Induced Radicals in Biphenyl Single Crystals

Biphenyl single crystals irradiated with γ rays at liquid nitrogen temperature have been investigated by electron paramagnetic resonance and optical absorption experiments. EPR spectra at room temperature exhibit a triplet characteristic separated by 39 gauss and each line of the triplet further splits to a triplet. The main triplet has been interpreted as being caused by hydrogen added biphenyl radicals. The splitting of each line of the main triplet is consistent with the calculated splittings of 2-hydro-biphenyl radicals and 4-hydro-biphenyl radicals. The presence of 3-hydro-biphenyl radicals could not be judged from the EPR spectra due to the broadness of the lines. In the optical absorption spectra at low temperature, obtained with the light polarized to the a-, b- and c'-axes of the crystals, nine bands were detected. Transition energies were calculated using SCF-C1 molecular orbital theory for the three kinds of the hydrogen added biphenyl radicals. By comparing the experimental spectra with the theoretical transitions of the three kinds of radicals, the bands at 666 nm and 424 nm have been assigned to the transitions of 2-hydro-biphenyl radicals, the 660 nm band to that of 3-hydro-biphenyl radicals, and the bands at 604 nm and 598 nm to the ones of 4-hydro-biphenyl radicals. The decays of these radicals at room temperature are very similar and upon annealing a new absorption band appears at 462 nm.     

Optical spectra of borate glasses containing Ti and Co in relation to their structure

The optical absorption spectra of borate glasses of the base composition (mol%) 35 (Na₂O+BaO)·65 B₂O₃, to which Ti and Co ions were introduced, have been measured in the range 190–900 nm. The addition of increasing amounts of TiO₂ up to 16 g/100 g glass, introduces an intense charge transfer band in the UV region that shifts towards longer wavelengths without imparting any coloration to the glass samples.Titanium ions are present as the Ti⁴ state and its addition produces glass of more coherent structure. The cobalt ions are found to be present in two symmetries; as CoO₆ units with absorption bands (denoted here as bands a and b) around 525–530 nm and 580–595 nm (respectively), and as CoO₄ units with absorption bands (denoted here as band-c) around 620–635 nm. Replacing Na ions by Ba ions or increasing the TiO₂ content favours the conversion of CoO₄ units into the CoO₆ ones.