Search

The Czochralski growth of Dy3+-doped (Lu1−xGdx)2SiO5solid solution single crystals with different mixtures of Lu2SiO5and Gd2SiO5oxides (x= 0, 0.2, 0.4, 0.6, 0.8, and 1) is reported. It was found that the (Lu1−xGdx)2SiO5crystals retain structural, physical, and optical properties of Lu2SiO5even for x= 0.8. Optical investigation of Dy:(Lu1−xGdx)2SiO5revealed that the structural disorder of the host brings about a strong inhomogeneous broadening of Dy3+spectral bands while influencing weakly rates of its radiative and nonradiative transitions. Dielectric characteristics of solid solution crystals are presented and discussed. Finally, (Lu1−xGdx)2SiO5solid solution crystals seem to be an attractive alternative to a Lu2SiO5host for the design of novel phosphors, radiation converters, and lasers owing to a significantly lower melting temperature and hence easier and less expensive manufacturing.

The aim of this research was to find out the way of the synthesis temperature reduction without deterioration of the phosphors optical properties. Since crystallization of Eu,Ca-α-sialon occurs by means of sialon crystallization from the oversaturated oxynitride liquid, thus a rise of the liquid phase amount could be performed not only via an increase of temperature but also through the application of the low eutectic additives. Al2O3 and AlF3 additives have been chosen as the sources of liquid at the reaction temperature. The syntheses were carried out in a graphite furnace at 1650°C and the powders were characterized for their phase composition, particles morphology, excitation and emission properties and their quantum yield of luminescence was compared. It has been found that alumina addition to the initial mixture of nitrides was the most effective in formation of sialon solid solution with a minor contamination with AlN. Emission intensity of sialon phosphor was doubled if they were synthesized with each of additives. Quantum yield of tested phosphors was over 0.85 if excited at 380 nm for alumina and similar for AlF3 modified composition. A significant particles refinement was observed if AlF3 was applied.

The purpose of the presented research was to compare the effect of changing the aluminium source in the mixture of initial powders on the properties of the final phosphor powder of Ca – α-SiAlON doped with Eu2+. The phosphor composition was designed as Eu0,048Ca0,752Si9,6Al2,4O0,8N15,2 and it was prepared by the solid state reaction in a temperature range of 1450-1650 °C. AlN and/or η-Al2O3 powders were used as a source of aluminium. It has been found that presence of aluminium nitride or oxide in the mixture of initial materials significantly changed the course of α-sialon formation, chemical composition of that solid solution and the resultant photoluminescence properties. It has been established that a small amount of η-Al2O3 with a suitable carbon addition was profitable for liquid formation and enhanced crystallization of Ca,Eu-α-sialon. The excessive oxide-rich liquid at reaction temperature led to sintering of phosphor particles and decreased emission intensity while lack of sufficient amount of liquid (nitrogen-rich starting composition) resulted in AlN presence and considerably reduced emission intensity of this phosphor.

Oxynitrides compounds are interesting for white LED industry because more covalent matrix's bonds in comparison to oxides enable to obtain higher color temperature of wLED. The Sialon's luminescence material doped by rare earth ions with high mechanical and chemical resistance and a broad emission band may become an alternative for garnet phosphors. The goal of the study was to investigate influence of divalent stabilizing cations on luminescence properties of M-α-Sialon doped with Eu2+ in order to estimate its potential for YAG:Ce replacement in WLEDs. The compound of general formula EuxM1-xSi9,6Al2,4O0,8N15,2, where M=Ca, Ba, Sr, was prepared by the solid state reaction method from the mixture of the relevant oxides, nitrides and carbonates. Synthesis was carried out at the temperature of 1650°C for 4 h in a reduction atmosphere (N2+CO). The structure and morphology of obtained powders were analyzed by XRD and SEM/EDS methods, respectively. Optical properties were investigated by excitation, emission and reflection spectra and compared to photoluminescence properties of standard YAG:Ce. The obtained specimens show the significant effect of synthesis parameters on the phase composition and intensity of emission of M-α-Sialon:Eu2+ powder.

Oxynitrides compounds are interesting for white LED industry because more covalent matrix's bonds in comparison to oxides enable to obtain higher color temperature of wLED. The Sialon's luminescence material doped by rare earth ions with high mechanical and chemical resistance and a broad emission band may become an alternative for garnet phosphors. The goal of the study was to investigate influence of divalent stabilizing cations on luminescence properties of M-α-Sialon doped with Eu2+ in order to estimate its potential for YAG:Ce replacement in WLEDs. The compound of general formula EuxM1-xSi9,6Al2,4O0,8N15,2, where M=Ca, Ba, Sr, was prepared by the solid state reaction method from the mixture of the relevant oxides, nitrides and carbonates. Synthesis was carried out at the temperature of 1650°C for 4 h in a reduction atmosphere (N2+CO). The structure and morphology of obtained powders were analyzed by XRD and SEM/EDS methods, respectively. Optical properties were investigated by excitation, emission and reflection spectra and compared to photoluminescence properties of standard YAG:Ce. The obtained specimens show the significant effect of synthesis parameters on the phase composition and intensity of emission of M-α-Sialon:Eu2+ powder.

We observed two ultrabroadband near-infrared (NIR) luminescence bands around 1.2 and 1.5?μm in as-grown bismuth-doped CsI halide crystals, without additional aftertreatment. Dependence of the NIR emission properties on the excitation wavelength and measurement temperature was studied. Two kinds of NIR active centers of subvalent bismuth and color centers were demonstrated to coexist in Bi:CsI crystal. The eye-safe 1.5?μm emission band with an FWHM of 140?nm and lifetime of 213?μs at room temperature makes Bi:CsI crystal promising in the applications of the ultrafast laser and ultrabroadband amplifier.

Optical spectra and luminescence decay curves were measured for thulium-doped YVO_4, GdVO_4, and LuVO_4 single crystals as a function of temperature in the 300–670K temperature region. In spite of structural similarity, the three systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found, in particular, that the peak value of the pump band absorption intensity diminishes by about 30% for Tm:YVO_4 and Tm:GdVO_4, and the effective emission cross section for the laser transition of Tm^3+ diminishes by a factor of 2 roughly when temperature increases from 300 to 500K. An unusually small quantum efficiency of the upper laser level in Tm:LuVO_4 has been derived from the analysis of luminescence decay curves.

High optical quality Nd-doped Sc_2SiO_5 crystal with size of diameter 27 mm×60 mm was obtained by Czochralski method. An x-ray diffraction pattern of Nd:SSO crystal confirmed that the as-grown crystal was isostructual with the SSO crystal. Absorption and emission spectra were recorded at 10 K. The Judd-Ofelt theory was applied to obtain standard parameters Ωt(t=2,4,6) and the fitting result of experimental absorption line strengths, which provided the F3/24 radiative lifetime (τ_rad) of 219 μs and the luminescence branching ratio β of 0.57 for the ^4F_3/2-^4I_9/2 laser transition. The stimulated emission cross section of 1.04×10^−19 cm^2 at 1074 nm was calculated using the Füchtbauer-Ladenburg equation. The ^4F_3/2 luminescence lifetimes with 215 μs at 10 K and 198 μs at 300 K were determined from luminescence decay curves, indicating high quantum efficiency in the Nd:SSO crystal. All these results showed that Nd:SSO would be a promising gain media in solid-state lasers.

Optical spectra and luminescence decay curves were measured for erbium-doped YVO_4 and GdVO_4 single crystals as a function of temperature in the 300 K-670 K temperature region. In spite of structural similarity the two systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found in particular that the intensity of parasitic upconverted emission excited at 978 nm depends weakly on temperature for YVO_4:Er^3+, whereas it decreases monotonously with increasing temperature for GdVO_4:Er^3+ and becomes negligibly small at 670 K. It was concluded that GdVO_4:Er^3+ may be a promising laser active material operating at high thermal loading conditions encountered in high-power diode-pumped IR lasers.