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.     

Radiation-Induced Radicals in Anthracene Single Crystals

EPR and optical absorption studies have been made on anthracene single crystals irradiated with electrons at liquid nitrogen temperature. Studies of annealing of the EPR spectra induced by irradiation at liquid nitrogen temperature revealed that they consisted of a broad singlet and two sets angular dependent lines. The angular dependence of the latter was studied and they were ascribed to the 9- and 1-dibenzo-cyclohexadienyl radicals. From comparison of the change in the EPR spectra with the change in the optical absorption spectra at room temperature, optical absorption bands at 535 and 675 nm were ascribed to 9- and 1-dibenzo-cyclohexadienyl radicals. An optical absorption band at 645 nm, which is created by irradiation at liquid nitrogen temperature and decays within two hours at room temperature was suggested to arise from the 2-dibenzo-cyclohexadienyl radical. The broad singlet, which is annealed below room temperature, was ascribed to the 9-anthracyl radical.     

Radiation induced color centers in 50PbO–50P2O5 glass

The effect of γ-irradiation in the dose range of 5 kGy up to 25 kGy on the optical absorption spectra of 50PbO–50P₂O₅ glasses is reported. The spectral absorption of these glasses before and after γ-irradiation was measured in the spectral range of 300–900 nm at room temperature. The radiation induced absorption in this spectral range shown to consist of two bands centered approximately at 545 nm and 730 nm. The fundamental absorption edge shifts generally to lower energies with increasing γ-irradiation dose up to 25 kGy in this glass sample. The intensity of the induced absorption bands increases linearly with increasing γ-irradiation dose. The higher energy band (HEB) may be due to a hole in a singly bonded non-bridging oxygen distant from a modifier cation, while the lower energy band (LEB) is also due to a hole in similar oxygen which is interacting with a neighboring cation.     

Absorption bands due to silver particles in the glasses containing halogen ions

The absorption bands due to silver particles formed in the glasses containing a small amount of halogen ions were measured and the peak positions were compared with those calculated by the Mie theory. The absorption peaks occurred at about 405–410 nm in the glasses without halogen ions. However, they shifted to far longer wavelengths in the halogen-containing glasses, occurring at about 470–510 nm in the glasses with Cl ions (0.26%) and at about 520–530 nm with Br ions (0.19%), respectively. The comparison of the experimental results with the calculated values on the peak position suggested that the absorption bands observed in the halogen-containing glasses heat treated for a prolonged time were due to nearly spherical silver particles formed in silver halide crystals.     

Optical absorption study on radiation damage in fluoride glasses

The effect of 1.7 MeV electrons on the coloration of fluorozirconate (ZBL) and fluorohafnate (HBL) glasses has been investigated. Irradiation can produce intense broad absorption bands at 325 nm and 253 nm in the glasses. However, the size and shape of the absorption bands in zirconate-based glass (ZBLA) which has Al³⁺ ions as network stabilizers is different from those in ZBL and HBL glass. The optical absorption bands due to self-trapped hole centers can be assigned from dichroic absorption measurements. It appears that the radiolysis damage mechanism may contribute to the coloration of these fluoride glasses.     

UV–visible and infrared absorption spectra of transition metals-doped lead phosphate glasses and the effect of gamma irradiation

Undoped and transition metals (TM 3d)-doped lead phosphate glasses were prepared. Ultraviolet–visible absorption spectra were measured in the range 200–1100 nm before and after successive gamma irradiation. Experimental results indicate that the undoped lead phosphate glass reveals before irradiation strong and broad ultraviolet absorption which is related to the co-sharing of absorption due to both trace iron impurities and lead ions (Pb²⁺). In the TM-doped glasses, characteristic absorption bands are obtained in both the UV and/or visible regions due to each respective TM ion in addition to that observed by the base undoped UV absorption. Gamma irradiation produces with the undoped glass a prominent induced ultraviolet broad band centered at about 300 nm originating mostly from the contribution of trace iron impurities and the visible spectra reveal markedly high shielding behavior towards successive gamma irradiation, due to the presence of both high content of heavy Pb²⁺ ions and the sharing of phosphate as a partner. With TM-doped samples, the observed induced bands are virtually varying and related to the type of the sharing TM ions. Infrared absorption spectra reveal in the undoped and TM-doped glasses characteristic structural phosphate groups mainly consisting of metaphosphate and pyrophosphate units. Transition metals are assumed to cause depolymerization of the phosphate glass network with different ratios but the changes in IR spectral data are limited due to the low doping level. Gamma irradiation of the samples is assumed to cause changes in the bond angles or bond lengths of the structural phosphate units within network as evident in the variation of the intensities of the IR bands.     

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.     

Crystal Structure and Third-Order Nonlinear Optical Properties Study of Tetraphenylporphyrin and Its Nickle Complex at Wavelength 532 nm and 1064 nm

Tetraphenylporphyrin (TPP) and its nickel(II) (NiTPP) complex have been synthesized, their crystal structures have been determined by means of X-ray single crystal diffraction. The TPP possesses good planarity in the porphyrin core, while in the complex the planarity disappeared. The central nickel(II) ion coordinates with four nitrogen atoms, which constructed a distorted square environment. Their third-order nonlinear optical properties have been studied using Z-scan technique at wavelength 532 nm and 1064 nm in picosecond (ps) domain. At 532 nm nonlinear absorption were observed, TPP shows two-photon absorption (TPA) combined with saturable absorption (SA), while NiTPP shows SA. At 1064 nm nonlinear refraction were observed, the molecular second hyperpolarizability γ of the NiTPP was about 1.4 times larger than that of the TPP.     

Growth of large-sized Ce:Y3Al5O12 (Ce:YAG) scintillation crystal by the temperature gradient technique (TGT)

In this work, Ce:YAG crystal with the size of ?4 in was successfully grown by the TGT method. The optical and scintillation properties of as-grown Ce:YAG crystals were investigated. Three obvious absorption bands at 223, 340 and 460 nm and two weak color-center absorption bands at 296 and 370 nm are observed in as-grown Ce:YAG crystal. Fluorescence with an emission peak at 398 nm is observed due to the color centers, and absorption bands of the color centers can be eliminated by annealing in O₂ or H₂ atmosphere at 1673 K for 24 h. Yellow-green fluorescence centered at 530 nm is found when the crystal was excited at 460 nm and the 530 nm excitation spectrum shows two peaks at 340 and 460 nm. X-ray fluorescence spectrum of as-grown crystal shows three emission peaks at 300, 360 and 530 nm. An average light output of 1360 phe/MeV and a single exponential decay with the decay time constant of 62.97 ns are found in as-grown Ce:YAG crystal.     

Effect of UV irradiation on Cu+-containing glasses

Optical absorption spectra of copper-containing silicate glasses were determined and the effects of UV irradiation on the spectra were studied. Oxalic acid was used as a reducing agent in order to obtain monovalent copper ions. Several absorption bands were observed as a result of UV irradiation at wavelengths of 430–480, 565–570, 620–690, 720–790, 800–900 and 307–310 nm. These bands were interpreted in terms of photochemical reaction and attributed to color centers, cupric ions (Cu¹⁺⁺), metastable copper atoms (Cu^o), and aggregates of copper atoms which were induced by UV irradiation.     

Radiation-induced defects in fluoride glasses

Fluorozirconate (ZBLA) and fluorohafnate (HBL) glasses have been exposed to ionizing radiation at room temperature, and the resulting defects have been characterized using optical absorption and electron spin resonance techniques. Prominent absorption bands were found to peak in the ultraviolet at 290 nm for the ZBLA glass and at 240 and 310 nm for the HBL glass. Two major electron spin resonance spectra having g values of 1.883 and 2.043 were induced in the HBL glass. Similar electron spin resonance spectra were found in the ZBLA glass. A third spectrum with a g value of 2.008 was also observed in the ZBLA material. The optical and electron spin resonance spectra in these glasses thermally annealed between room temperature and 300°C. Possible models for the defects are discussed.     

The dielectric properties of as-received and gamma irradiated fused silica

Audio frequency capacitance and conductance measurements have been carried out on 15 kinds of fused silica over the temperature range 5.5–380 K. The results are used to arrive at corresponding values for the complex dielectric constant. It is shown that the relative strengths of the three relaxations observed in as-received fused silica are characteristic of the type of fused silica. In addition, it is found that one of the relaxations can be destroyed by gamma rays and that the destruction is accompanied by the creation of a lower activation energy relaxation. A corresponding growth of optical absorption bands in the visible portion of the spectrum is observed. The gamma-ray sensitive relaxation is attributed to an aluminum-alkali center and the gamma-ray induced relaxation is attributed either to an aluminum-oxygen-hole center or to a “non-local” alkali ion. Finally, accurate values for the real part of the dielectric constant at various temperatures are presented.     

Spectroscopic and structural properties of Cr in silicate glasses: Cr does not probe the average glass structure

Cr³⁺-containing alkali, alkaline earth and mixed alkali-alkaline earth silicate glasses have been investigated using Cr K-edge extended x-ray absorption fine structure (EXAFS) and optical absorption spectroscopy. The local environment of Cr³⁺ appears similar in all glasses regarding EXAFS analysis, in particular for Cr-O distance (1.99 Å). By contrast, optical absorption spectra show variations of crystal field values and disorder effects with the nature of the modifier cation, revealing that some differences exist in the local surrounding of Cr³⁺ in glasses. In addition, in mixed alkali-alkaline earth glasses optical absorption parameters remain close to the values found in binary silicate glasses with the same alkali, which reveals a preference for alkalis in the surrounding of Cr³⁺. As a whole, these data show that Cr³⁺ is not probing the average glass structure and demonstrate its heterogeneous distribution at a local scale.     

The effect of different alkali ions on the optical and magnetic properties of R2O−B2O3 + MnO2 glasses

Spectrophotometric, magnetic studies and chemical analyses of a number of binary alkali borate glasses containing manganese were carried out in order to throw some light on the structure of these glasses and on the forms in which manganese exists in borate glasses.The results obtained could be explained on the basis that manganese exists in glasses in two different states; divalent manganese coordinated with tetrahedral arrangements with oxygen and shows four bands at about 400, 460, 490 and 530 nm with very low molecular extinction coefficients, and trivalent manganese assuming octahedral symmetry having a broad band at 470–500 nm which under some conditions shows splittings to two or three peaks with high values of molecular extinction coefficients.The paramagnetic character of the glasses containing manganese is usually attributed to the presence of five and four unpaired electrons in the divalent and trivalent states of manganese, respectively. The ratio of trivalent to divalent manganese ions depends on several factors, including the polarisability of the oxygen ligands surrounding the manganese ions, the presence of bridging and non-bridging oxygen and the type of alkali ion present.     

Glow curves of flux-grown NaMgF3 crystals

Glow curves and optical absorption spectra of X-irradiated flux grown crystals are studied. Two glow peaks at 370, 585 K and three shoulders at 420, 540 and 610 K are obtained. Optical absorption studies reveal two absorption bands at 405 and 475 nm and a well defined peak at 295 nm. Room temperature annealing and bleaching studies have suggested that the glow peaks at 370 and 585 K may correspond to impurities and F-centers of 295 nm band respectively. The other shoulders at 420, 540 and 610 K are attributed to other F-aggregate centers. The glow peaks are analysed using first order kinetics.     

Czochralski growth and optical spectral properties of GInGG: Cr single crystal

GInGG: Cr³⁺ crystal was grown by the Czochralski technique for the first time. The Optical absorption and fluorescence spectra were measured at room temperature and 77 K. Two wide absorption bands occur at 457 and 643nm. A highly efficient emission from 670–1050nm with a peak at 771nm was observed at 289K. The energy levels were fitted by means of Tanabe-Sugano matrices and the values of Dq, B and C were calculated to be 1555, 637 and 3226 cm⁻¹, respectively.     

Neodymium ion environment in germanate crystals and glasses

Absorption and fluorescence spectra are presented for neodymium-doped alkali germanate and bismuth germanate glasses and crystals. Narrower spectral components and a shift in intensity distribution toward shorter wavelengths for the composite bands corresponding to the principal neodymium absorption and fluorescence transitions are observed as the radius of the glass modifier ion is increased (Li⁺Na⁺K⁺). These changes in component band width and intensity distribution become more pronounced as the concentration of large radius modifier ion is increased, and result in effectively narrower widths for the fluorescent bands involved in laser emission. Optical spectra for neodymium in a sodium germanate single crystal show broad bands characteristic of those of glasses. Electron microprobe scans reveal non-uniform distribution and clustering of neodymium in alkali germanate crystals. Narrow, temperature sensitive bands similar to those of neodymium in other crystals are found for single crystal and polycrystalline neodymium-doped bismuth germanate, while the glass exhibits broad bands. Substitutional replacement of Bi³⁺ with Nd³⁺ in the bismuth germanate crystal lattice is indicated from the optical spectra but the environment of neodymium in crystalline sodium germanate appears to have only short-range order. The difficulty encountered in introducing neodymium into substitutional positions in alkali germanate crystals may result from the charge difference between neodymium and the alkali cations as well as the oxygen: germanium ratio of these compounds, which favors glass network formation rather than crystallization.     

Dye centres in magnesium doped corundum monocrystal

Results of absorption spectra studies in Mg doped Al₂O₃ monocrystals are described. It is shown that due to Mg doping dye centres appear together with the associated additional absorption bands with maxima at 585, 475 and 260 nm. Kinetics of the formation (destruction) of these centres) of these centres in the process of thermal treatment is considered. An assumption on the nature of dye centres and the related absorption bands is proposed together with an evaluation of oscillator strength. Dependences of diffusion coefficients of the subject centres on thermal treatment temperatures are derived.     

Matrix effect on absorption and infrared fluorescence properties of Bi ions in oxide glasses

Absorption and fluorescence spectra of Bi ions in multi-component oxide glasses melted in air were measured. Absorption bands in the range of 400–1000 nm and fluorescence bands at round 1210 nm were only detected in the silicate, borosilicate, borate, and germanate glasses with or without a small amount of alkali or alkaline-earth oxides. The relative IR fluorescence intensity increased with decreasing basicity of matrix glasses and with adding the Al₂O₃. The compositional dependence of the relative IR fluorescence intensity and the IR fluorescence mechanism are discussed in terms of redox reaction and energy diagram of bismuth-related species in oxide glasses.     

Structure and properties of silver phosphate glasses — Infrared and visible spectra

The infrared and visible spectra of glasses in the Ag₂OP₂O₅ glass-forming system were obtained. The infrared data were interpreted as indicating the presence of polymeric chains in these glasses. The partial covalent nature of the AgOP bond was discussed. A mixed NaPO₃AgPO₃ glass showed no unexpected bands in the infrared spectrum, again showing that silver is behaving in a manner similar to alkali metal ions in phosphate glasses. The shift in the absorption edge in the visible spectra of glasses of different Ag/P ratio was shown to arise from either an increase in the concentration of nonbridging oxygens with increasing silver content, or the presence of colloidal silver metal particles.