Andrey Novoselov

Photoluminescence of Bi3+ in Y3Ga5O12 single-crystal host

Photoluminescence spectra and decay kinetics within 10–350 K were measured in the Bi-doped Y3Ga5O12 single crystal prepared by the micro-pulling-down technique. Temperature dependences of the decay times and the integrated emission intensities obtained from the experiment were simulated using a phenomenological two-excited-state-level model. The model provided quantitative parameters of the involved excited state levels of the Bi3+ luminescence centre in this host. The results are discussed in the light of already published data obtained for other Bi-doped compounds. The influence of the defects and structural irregularities of the host on the Bi3+ emission characteristics is discussed as well.

Scintillation Properties of 2-Inch-Diameter

Pr:LuAG crystals possess interesting properties, such as high density, high light yield, and very fast 5d-4f emission decay time. Recently, we developed a Pr:LuAG single crystal with a diameter of 2 inches for scintillator applications, such as medical imaging. In this study, Pr-doped Lu3Al5O12 (Pr:LuAG) single crystals with a diameter of 2 inches were grown by means of the Czochralski method; a body length of up to 90 mm was achieved. The Pr:LuAG crystals produced a homogeneous light yield with approximately 2.5 times less intensity compared to that produced by a conventional Ce:LSO crystal. A sample with dimensions of 5 mm times 5 mm times 1 mm exhibited energy resolutions of 4.8% at 662 keV, as measured by using a photomultiplier (PMT: Hamamatsu H6531), and 5.8% at 662 keV, as measured by using an Avalanche photodiode (APD: Hamamatsu S8664-55). The Pr:LuAG crystals exhibited a very fast rise time of approximately 0.4 ns, excited by a pulsed X-ray at room temperature. The decay time was approximately 18 ns, along with a noticeable presence of slower decay components (with a decay time of 55.0 ns). Furthermore, the Pr:LuAG crystals showed good linearity between the energy and pulse height within approximately 4% of the standard deviation in the range from 122 keV (152Eu) to 1.4 MeV (241Am) .

{\rm Pr}:{\rm Lu}_{3}{\rm Al}_{5}{\rm O}_{12}

Zr,Pr-codoped and Si,Pr-codoped single crystals were grown from the melt by the micro-pulling-down method. The effect of Zr/Si-codoping on YAIO3:Pr scintillation properties, such as radioluminescence, scintillation light yield and decay time, was investigated. Absorption spectra of as-grown and air-annealed samples reveal the presence of color centers. The possible nature of the charge traps detected by high temperature thermoluminescence is discussed.

(LuAG) Single Crystal

Refractory rare-earth sesquioxides (RE2O3, RE = Y, Lu, Sc) are promising host materials for solid-state lasers due to low phonon energy and high thermal conductivity. In this work, we investigated thermodynamic properties of Yb3+-doped Y2O3 single crystals, doping level ≤15 mol % Yb3+ grown by the micro-pulling-down method (µ-PD). The thermal diffusivity lowers with increasing Yb3+ content from 7.2 to 2.37 ×10-6 m2 s-1, heat capacity from 0.44 to 0.403 J g-1 K-1, and thermal conductivity from 15.94 to 5.35 W m-1 K-1. Spectroscopic data are discussed.

Crystal Growth and Scintillating Properties of Zr/Si-Codoped

Eu1% LiCaAlF 6 (LiCAF) single crystal (nominal composition) with 2 mm in diameter and 35 mm in length was grown by the micro-pulling-down (μ-PD) method. Emission from Eu2+ centers were observed in α-ray excited luminescence. Neutron response was compared with Li-glass (GS20, Saint-Gobain) using 252Cf. It is found that the decay time of Eu1%:LiCAF is 1.6 μsec, which is slower than that of GS20. Light yield of the Eu:LiCAF single crystal indicated from 1.5 times to twice as large as that of GS20. Therefore, when light yield of GS20 is 6000 photons/neutron, that of Eu:LiCAF single crystal is estimated from 9000 to 13000 photons/neutron.

Thermal and Optical Properties of Yb3+-Doped Y2O3 Single Crystal Grown by the Micro-Pulling-Down Method

The RE2O3 (RE = Y, Lu, Sc) sesquioxides are promising host materials for solid-state lasers owing to their low phonon energy and high thermal conductivity. Our results demonstrate that the micro-pulling-down method is a viable approach to the single-crystal growth of refractory rare-earth sesquioxides with melting points over 2400°C. The method yields chemically homogeneous single-crystal rods of high crystallinity. We also present thermal conductivity data for Yb-doped Y2O3 and Lu2O3 and for Tm-doped Y2O3.

Neutron responses of Eu 2+ activated LiCaAlF 6 scintillator

Pr-doped YAlO3 (0.1, 0.5, 1, 2, 3, 4, 5, and 6 mol % Pr6O11) single crystals were grown by the micro-pulling-down method and their optical and luminescence properties were investigated in the range 80–300 K. Dominant 5d–4f double-peak emission at 254 and 282 nm was observed both in radio-and photoluminescence, and was accompanied by weak 4f–4f luminescence at 495 and 620 nm. The 5d–4f emission shows almost no temperature dependence below 300 K, and achieved radioluminescence intensity is more than 15 times higher than that of Bi4Ge3O12.

Micro-pulling-down: A viable approach to the crystal growth of refractory rare-earth sesquioxides

Ytterbium- and neodymium-substituted yttrium aluminum garnets were obtained by hydroxide coprecipitation and by the cryochemical method. A continuous series of solid solutions in the Y3Al5O12 — Yb3Al5O12 system and limited solid solutions (NdxY1 − x)3Al5O12 (0 ≤ x ≤ 0.19) were obtained. The synthetic methods used made it possible to reduce the synthesis temperature from 1800 to 950°C and to obtain more homogeneous and nanosized material.

Scintillating properties of Pr-doped YAlO3 single crystals grown by the micro-pulling-down method

Using the micro-pulling-down method, undoped and Pb-doped LiCaAlF6 single crystals were grown. Structural parameters studied by X-ray powder diffraction were consistent with P3 macr1c space group. High volatility of PbF2 leads to low dopant concentration, highest level achieved was 0.56 mol% according to electron probe micro-analysis data. Recorded absorption spectra demonstrate intense band within 192-200 nm. Radioluminescence emission at 208 nm shows the decay time of about 19 mus at room temperature.

Synthesis and study of yttrium aluminum garnets doped with neodymium and ytterbium

Pr:LuAG has interesting properties of high density, high light yield and a very fast 5d-4f emission decay time. Recently we have develop 2-inch-diameter Pr:LuAG single crystal for scintillator applications such medical imaging and high-energy physics. In this report, we study uniformity of the light yield, energy resolution, decay time and gamma-ray response in the range from 59.5 keV (241Am) to 1.4 MeV (241Am).