掺杂稀土LiNbO_3晶体的生长和光谱性质

在一致熔化的熔料里,用提拉法生长了 LiNbO_3∶TR(TR=Nd、Er、Er+Mg、Ho、Sm、Eu)单晶。测量了它们的吸收光谱和荧光光谱。     

Cathodoluminescence study of CdTe crystals doped with Bi and Bi:Yb

Bi doped and Bi and Yb codoped CdTe crystals grown by the Bridgman method have been characterized by cathodoluminescence (CL) in the scanning electron microscope. CL images show a dense network of highly decorated grain boundaries in the Bi doped samples and dopant striations in the codoped crystals, attributed to the presence of Yb. Bi contributes to the appearance of the A luminescence band at 1.43 eV. The influence of Yb dopant on the CL spectra is discussed.     

Photoelectric Fields and Band Gap in Doped Lithium Niobate Crystals

Photoinduced light scattering and optical spectroscopy have been used to study the photorefractive effect and determine the band gap in nominally undoped congruent and stoichiometric lithium niobate crystals, as well as in a series of congruent LiNbO₃ crystals doped with Mg, Zn, B, Gd, Y, and Er cations and LiNbO₃ single crystals codoped with Mg:Gd, Mg:Fe, Mg:Y, and Mg:Ta.     

Structure and optical properties of LiNbO<Subscript>3</Subscript>:ZnO (3.43–5.84 mol %) crystals

LiNbO₃:ZnO (3.43–5.84 mol %) crystals have been studied using Raman spectroscopy and fullprofile analysis of X-ray diffraction data. The results demonstrate that, at ZnO concentrations above 3.95 mol %, their structure is free of Nb_Li basic defects, which are characteristic of congruent lithium niobate crystals. Increasing the Zn concentration leads to changes in the arrangement of structural units in the cation sublattice along the polar axis and distorts the BO₆ (B = Nb, Li, Zn, or a vacancy) oxygen octahedra. In the Raman spectra of the crystals, the width of the line at a frequency of 876 cm^–1, which corresponds to stretching modes of the oxygens in the BO₆ octahedra, has been shown to increase considerably, which may be due to changes in the character of bonding in the B–O–B bridges in response to changes in the Zn concentration in the crystals. The gradual increase in the electro-optical coefficients of the LiNbO₃:ZnO crystals with increasing zinc concentration can be accounted for by changes in the ionic contribution to these bonds.     

Application of infrared emission spectroscopy to the thermal transition of indium hydroxide to indium oxide nanocubes

Cubic indium hydroxide nanomaterials were obtained by a low-temperature soft-chemical method without any surfactants. The transition of nano-cubic indium hydroxide to cubic indium oxide during dehydroxylation has been studied by infrared emission spectroscopy. The spectra are related to the structure of the materials and the changes in the structure upon thermal treatment. The infrared absorption spectrum of In(OH)(3) is characterized by an intense OH deformation band at 1150 cm(-1) and two O-H stretching bands at 3107 and 3221 cm(-1). In the infrared emission spectra, the hydroxyl-stretching and hydroxyl-bending bands diminish dramatically upon heating, and no intensity remains after 200 °C. However, new low intensity bands are found in the OH deformation region at 915 cm(-1) and in the OH stretching region at 3437 cm(-1). These bands are attributed to the vibrations of newly formed InOH bonds because of the release and transfer of protons during calcination of the nanomaterial. The use of infrared emission spectroscopy enables the low-temperature phase transition brought about through dehydration of In(OH)(3) nanocubes to be studied.     

Investigation on the defect structure and light-induced scattering of LiNbO3:Fe:Mg:Zr crystals with various Li/Nb ratios

A series of LiNbO₃:Fe:Mg:Zr single crystals with various Li/Nb ratios in the melt were grown by the Czochralski method in the air. The ultraviolet–visible and infrared transmittance spectra were measured to investigate the defect structures of these crystals. A new vibration peak of 3502 cm⁻¹ was observed in infrared transmittance spectra. The sequence of substitution was concluded according to the spectroscopic characterization. The light-induced scattering of LiNbO₃:Fe:Mg:Zr crystals was characterized quantitatively via the incident exposure energy, and the relationship between the defect structures and light-induced scattering was discussed.     

Luminescence efficiency enhancement of BaZr(BO3)2:Eu with Si or Al addition

Si4+ and Al3+ doped BaZr(BO3)2:Eu phosphors were prepared by solidstate reaction. BaZr(BO3)2:Eu3+, BaZr(BO3)2:Eu3+, Si4+ and BaZr(BO3)2:Eu3+, Al3+ were characterized by X-ray diffraction spectra (XRD) and photoluminescence spectra. After codoped with Si or Al, the charge-transfer state (CTS) band of Eu3+-O(2-) shows blue shift accompanied by increasing intensity due to shorter ionic radius and stronger electro negativity of Si or Al compared with Zr4+. The high value of asymmetric ratio R(2-1) and omega2 of BaZr(BO3)2:Eu3+ with Si or Al codoping indicates a less symmetrical local structure of Eu3+. This implies that the quantum efficiencies of the 5D0 level of these complexes can be enhanced by doping with Si and Al respectively. Calculation of the Judd-Ofelt parameters of Eu3+ under different crystal fields gives similar results.     

Investigation on the growth and structure of Fe-doped near-stoichiometric LiNbO3 crystal

The Fe-doped near-stoichiometric LiNbO₃ crystal has been grown from the Li-rich melt by Czochralski method. The UV-Vis absorption spectra, IR transmittance spectra and X-ray diffraction were measured and used to study the defect structure of the crystal. Compared with that of congruent Fe:LiNbO₃, in near-stoichiometric Fe:LiNbO₃, the lattice parameter reduces, the basal absorption edge shifts towards shorter wavelength, and the OH stretching vibration absorption band shifts towards the lower wavenumber side (3466 cm^–1) in the Fe-doped near-stoichiometric LiNbO₃.     

Nonlinear Optical Properties of Ba3R(BO3)3(R = Y, Ho–Lu) Polar Crystals

Ba₃R(BO₃)₃(R = Y, Ho–Lu) crystals were prepared by a flux growth process, and there nonlinear optical properties were characterized by second harmonic generation measurements. The optical nonlinearity of the crystals was found to increase as the ionic radius of the rare-earth cation decreases.     

Manifestation of structural features of LiNbO<Subscript>3</Subscript>:Zn and LiNbO<Subscript>3</Subscript>:Mg crystals in their IR absorption spectra in the stretching region of OH<Superscript>–</Superscript> groups

Analysis of IR absorption spectra of LiNbO₃:Zn (0.04–4.46 mol % ZnO) and LiNbO₃:Mg (0.19–5.91 mol % MgO) single crystals in the stretching region of OH^– groups has been used to gain insight into composition-dependent structural changes in the crystals. The results demonstrate that, characteristically, the OH^– groups occupy different sites in the doped and congruent LiNbO₃ crystals and have different quasielastic O–H bond constants in their structure. In stoichiometric lithium niobate crystals, all of the OH^– sites and quasi-elastic O–H bond constants are identical. At threshold Zn and Mg dopant concentrations, the frequencies, widths, and intensities of the observed lines change sharply. The linewidths in the spectra of the LiNbO₃:Zn crystals near their first concentration threshold (≈2.0 mol % ZnO) and the LiNbO₃:Mg crystals near their first and second concentration thresholds (≈3.0 and 5.5 mol % MgO) decrease markedly, indicating ordering of the position of the OH^– groups in the structure of the crystals.