We present a combined experimental and theoretical investigation on the surface electronic structure of truly bulk ZnGa2O4, a transparent conducting oxide with an ultra-wide band gap of 4.6 eV. Angle-resolved photoelectron spectroscopy, X-ray photoelectron spectroscopy and low-energy electron diffraction were used to analyze the electronic band structure, band bending and surface reconstruction respectively. In combination with density functional theory, the experimental results will be discussed to provide the very first insights on the surface electronic properties of ZnGa2O4, to motivate future investigations.
In this communication we report initial results of studies on x-ray and VUV excited luminescence of YAP and YAG crystals activated with Pr3+ and YAP activated with Ce3+. Excitation and luminescence spectra of Pr3+ and Ce3+ d-f and Pr3+ f-f emissions and luminescence time profiles under pulsed synchrotron excitation are presented and analyzed in order to identify and characterize various host-to-ion energy transfer channels. The results support the notion that direct and trap mediated capture and recombination of holes and electrons via Pr3+ or Ce3+ ions provide the dominant mechanism of radio luminescence production in both YAP and YAG crystals.
The results of examinations of spectroscopic properties and generation parameters of new active media, i.e., Er3+ and Yb3+ doped YAG crystals are given. Erbium and ytterbium doped YAG single crystals were obtained by the Czochralski method. The spectral properties and laser characteristics were investigated. Absorption spectra of Er3+ and Yb3+-doped active media were measured in the spectral range 190 divided by 5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectrofluorimeter using a diode laser as an excitation source. The measurements of the lifetime of the Er3+ ions in the upper laser level of the samples were made by the direct method with pulse excitation. We present also the result of investigations on spectroscopic properties and non-linear absorption effect in YAG:Co2+ crystal-new absorber used for the systems generating giant-pulse radiation at 1.5 micrometers .
Growth conditions for Nd:YVO4 crystals and some optical properties are presented. The obtained Nd:YVO4 crystal shows lower content of point defects and consequently, lower susceptibility to ionizing radiation. ESR measurements show the presence of V ions in interstitial sites with another than 5t valency. Obtained by Czochralski method crystals reveal very good optical properties, some of which are better than for Nd:YAG.
Lithium niobate crystals doped with Dy3+ ions were grown by the Czochralski method. The doping concentrations were 0.3, 1, and 1.7 at.%, respectively. The dopant distribution was measured by the electron microprobe 'JOEL-JXA 50 A'-type device, and from these measurements the segregation coefficient has been found to be close to unity (k approximately equals 0.8). Optical homogeneity of crystals was investigated by the conoscopic and polarimetric methods. For the Z-optical axis direction it was found that the maximum residual birefringence (not exceeding 1.5 multiplied by 10-4), involved by residual stresses, occurred at the perimeters of the crystals, and the remaining crystalline areas were almost entirely free from excessive stresses. The absorption characteristics in the wavelength range of 200 - 6000 nm were measured. The photoluminescence characteristics were also measured in the visible part of the spectrum. It has been found that an important feature associated with luminescence of the Dy3+ in LiNbO3 is its high intensity and long decay time. From this it can be concluded that LiNbO3:Dy3+ is particularly well suited for visible lasers.
Lithium niobate crystals doped with Pr3+ or Yb3+, as well as double doped with Yb3+ and Pr3+ ions were pulled by the Czochralski method. The doping concentration spread distributions were measured for each ion by the electron microprobe. The optical homogeneity of crystals was investigated using the conoscopic and polarimetric techniques. The absorption characteristics were also investigated. In the absorption spectra a careful attention has been paid to the peak associated with OH group, since from this one can conclude on the location of the doping ions in the crystal lattice.
In this work practical investigations of residual stresses in LiNbO3 crystals measured by the computer-controlled imaging polarimeter are compared with theoretical model developed for oxide crystalline materials. A good qualitative agreement has been found between theory and experiment regarding residual stress distributions in wafers cut out perpendicularly to the crystal's growth axis.