Valery Chani

Temperature Dependence of Scintillation Properties of Bright Oxide Scintillators for Well-Logging

Scintillation characteristics such as the pulse height, energy resolution, and decay time of single crystals of Tl-doped NaI (Tl:NaI), Ce-doped Lu2SiO5 (Ce:LSO), Ce-doped YAlO3 (Ce:YAP), Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG), Pr-doped Lu3Al5O12 (Pr:LuAG), undoped LuAG, and Ce-doped Y3Al5O12 (Ce:YAG) transparent ceramics were compared at 25–150 °C to simulate well logging conditions. For increasing temperature, the light output of the scintillators decreased, mostly because of thermal quenching. Among these samples, Pr:LuAG demonstrated the highest scintillation performance at 150 °C.

(Tb, Yb)3Al5O12 garnet : crystal-chemistry and fiber growth by micro-pulling-down technique

Abstract A process is reported for fiber crystal growth of (Tb,Yb) 3 Al 5 O 12 from mixed Tb 3 Al 5 O 12 –Yb 3 Al 5 O 12 melt using micro-pulling-down technique. A model which allow to predict segregation coefficients for different rare-earth cations in mixed garnet crystals is reported, its key feature being a selection of couple of the cations which do not fit to the equilibrium size of the dodecahedral site in equal degree. Such an approximation was found to be applicable for the Tb 3 Al 5 O 12 –Yb 3 Al 5 O 12 system. Therefore the uniform and macro defect free crystals were successfully grown from melt of about Tb 2.2 Yb 0.8 Al 5 O 12 composition with a pulling down rate of up to 2 mm/min.

Growth of Ca3(Li,Nb,Ga)5O12 garnet crystals from stoichiometric melts

Abstract Ca 3 Li x Nb (1.5 + x ) Ga (3.5 − 2 x ) O 12 garnets were synthesized and the conditions of the crystal growth are established. The measured lattice constants are about 12.54 A irrespective of x . It was found that the Ca 3 Li 0.275 Nb 1.775 Ga 2.95 O 12 garnet melts congruently at about 1450°C. Transparent and bubble-free crystals of x = 0.25 and 0.275 were grown by both modified micro-pulling down and Czochralski techniques in air using Pt crucibles. Results of solid state reaction data of other garnets are also discussed. An absorption spectrum is also reported.

Preparation and characterization of Yb:Y3Al5O12 fiber crystals

Abstract A micro-pulling-down process employing Ir crucibles and RF heating has been used to grow single crystal fibers of Yb-doped Y 3 Al 5 O 12 garnet (YAG). Single crystals ranging up to 550 mm in length have been produced. The fibers were about 1 mm in diameter and were seeded-grown in the direction. Results of X-ray rocking curve measurements and transmittance data were used to discuss the crystalline perfection of the fibers. The effective segregation coefficient of Yb 3+ in the process described is reported to be slightly less than 1.0 at a growth rate of about 5 mm/min.

Correlation between Segregation of Rare Earth Dopants in Melt Crystal Growth and Ceramic Processing for Optical Applications

The paper deals with segregation of rare earth doping cations in solid-state hosts. Increased concentration of Ce3+ and Nd3+ on the grain boundaries of transparent garnet optical ceramics was recently reported. These experimental results correlate well with low segregation coefficients of Ce3+ and Nd3+ large rare earth cations and the higher segregation coefficients for small rare earth cations like Yb3+ in the garnet structure observed in the melt crystal growth and thin film liquid phase epitaxy from flux. Thus, the segregation in solid-state grain growth is qualitatively similar to that observed in the melt/flux growth of the garnet single crystals. The data on segregation in the melt/flux crystal growth are widely available and can be used for preliminary estimation of the dopant distribution in the ceramics produced from the solid state. This information could help to predict distribution of doping cations in the solid state hosts that is important in development of uniform and highly efficient optical materials.

Crystal Growth and Evaluations of

In order to develop novel scintillating materials, we grew 0.5 mol%, 1 mol%, and 3 mol% Nd-doped LuLiF4 scintillators by the micro-pulling down method, because LuLiF4 has a very wide band gap and Nd3+ shows fast and intense 5d-4f emission as a luminescence center. The transmittance and emission peaks were examined in these three samples by using our original spectrometer made by Bunkou-Keiki Company. At wavelengths longer than 180 nm, approximately 60-80% transmittance with three absorption peaks around 140, 160 and 175 nm and emission peak at approximately 180 nm were observed for all the crystals. Light yields and decay time constants of the samples irradiated by 241Am γ-ray were measured using photomultiplier tubes R8778 (Hamamatsu). The light yield of the 1 mol% doped LuLiF4 was 700 photons/5.5MeV α that is much greater than that of Nd:LaF3 scintillator (100 photons/5.5MeV α). As for decay time profiles, the main component of Nd:LuLiF4 was 12 ns in the case of α-ray irradiation. 137Cs 662 keV γ-ray photoabsorption peak was detected in 1 mol% doped LuLiF4 only, and the light yield was 300 ph/MeV.

{\hbox {Nd}}{\hbox {:LuLiF}}_{4}

Crack-free, transparent and colorless fiber single crystals with the size of 0.8–1.2 mm in diameter and 20–80 mm in length were grown from the melts of NaxCa2.5 − x2Mg2V3O12 where x = 0.0–1.0 by the micro-pulling-down method. The crystals grown from stoichiometric, NaCa2Mg2V3O12, and Na+-rich (x < 1.0) melt in air were transparent and gray colored. It was found that lower the x value, higher is the uniformity of lattice parameters of the solidified fraction. Maximal uniformity was achieved for the Ca2.5Mg2V3O12 crystals of less than ±0.001 A.

Scintillators for Different Nd Concentration

High quality oxide and fluoride single crystals for optical, piezoelectric and other applications have been grown by advanced crystal growth techniques. La3Nb0.5Ga5.5O14 and La3Ta0.5Ga5.5O14 piezoelectric single crystals of size and quality comparable to La3Ga5SiO14 (langasite), have been produced. The piezoelectric and device properties of the crystals were investigated. A search for new langasite-type materials was also performed. Growth conditions of (La,Sr)(Al,Ta)O3 and Ca8La2(PO4)6O2 single crystals are discussed. These crystals have excellent lattice matching with GaN, a promising material for optoelectronic devices. Promising optical micro-crystals—K3Li2Nb5O15, KNbO3 and Y3Al5O12—and new structural materials, Al2O3Y3Al5O12 eutectic fibers, have been grown by the micro-pulling-down (μ-PD) technique. The advantages of the μ-PD technique have been shown. Ce-doped fluoride single crystals—LiCaAlF6, LiYF4 and BaLiF3—have been grown for solid state UV laser applications. Growth results and optical characterizations are discussed.

Growth of vanadium garnet fiber crystals and variations of lattice parameter

Using appropriate substitutions in KTiOPO4 (KTP), new crystal compositions having the same highly stable structure, have been found. The preparation of Zr4+- and V5+-substituted crystals of KTP and KTiOAsO4 (KTA) is reported. Substitutions of Nb5+Si4+ and Nb5+Ge4+ for Ti4+P5+ and Ti4+As5+ cation pairs were studied in an attempt to modify the structure. Results showed that crystals of composition KTiOAsO4:KNbOGeO4 (1:1) could be grown from melts of the almost same composition at ∼ 1100°C. Crystals prepared from stoichiometric melts had the KTP structure and exhibited second harmonic generation.

Crystal growth of oxide and fluoride materials for optical, piezoelectric and other applications

Present work describes the first detailed γ-ray light yield of Ce3+ perturbed emission in CaF2 host. (1-, 3-, 5-, 10-, and 20-mol %-) Ce3+-doped single crystalline CaF2 scintillator crystals were grown by the micro-pulling-down method. Their transmittances were measured to be approximately 80% at UV to visible wavelengths. All the crystals exhibited emission peaks at approximately 330 nm, which were identified as the Ce3+ perturbed emission, when they were irradiated by 1 GBq 137Cs. The photoluminescence decay kinetics was measured to be about 40 ns for all the crystals. Scintillation light yield in unit of photons/MeV (ph/MeV) was measured, and the 5% sample showed the highest light yield of around 900 ph/MeV with 2 µs shaping time.