In this review, the major achievements and research and development (R&D) trends from the last decade in the field of single crystal scintillator materials are described. Two material families are included, namely, those of halide and oxide compounds. In most cases, the host crystals are doped with Ce3+, Pr3+ or Eu2+ rare earth ions. Their spin- and parity-allowed 5d–4f transitions enable a rapid scintillation response, on the order of tens to hundreds of nanoseconds. Technological recipes, extended characterization by means of optical and magnetic spectroscopies, and theoretical studies are described. The latter provide further support to experimental results and provide a better understanding of the host electronic band structure, energy levels of specific defects, and the emission centers themselves. Applications in medical imaging and dosimetry, security measures, high-energy physics and the high-tech industry, in which X(γ)-rays or particle beams are used and monitored, are recognized as the main driving factor for R&D activities in this field.

Recent R&D Trends in Inorganic Single-Crystal Scintillator Materials for Radiation Detection

Why so deep research on Yb3+-doped optical inorganic materials?

http://lib.fibopt.ru/Articles/PAPER/GPI/OptMat-2007-AP-96.pdf

Challenge and study for developing of novel single crystalline optical materials using micro-pulling-down method

Concentration dependence of Mn(2+) luminescence in NaCaPO(4)/Mn(2+) is investigated by structural analyses and optical and laser excitation spectroscopies in the temperature range 19-300 K. NaCaPO(4)/Mn(2+) forms solid solution over the Mn(2+) concentration range 1.0-22 mol %. We observe the red shift and unusual band narrowing of Mn(2+) emission by increasing Mn(2+) concentration in NaCaPO(4). The lifetime of Mn(2+) emission lengthens unexpectedly for higher Mn(2+) concentration. The results are discussed in relation with crystal structure, photon reabsorption, exchange interaction, and energy transfer and energy migration in NaCaPO(4)/Mn(2+).

Emission Red Shift and Unusual Band Narrowing of Mn2+ in NaCaPO4 Phosphor

Fifty years of advances in solid-state laser materials

We have grown high-quality LuAG:Yb3+ crystals with 0.75, 3.8, 10, 12, 15, 20, and 50 at. % concentrations by the vertical Bridgman method. With low-temperature spectroscopy the Stark sublevel structure of the 2F7/2 ground state and the 2F5/2 excited state has been determined. With room-temperature spectroscopy, the emission cross section was found to be 3×10−20 cm2, being 1.5 times the YAG:Yb3+ emission cross section. The luminescence quantum efficiency was measured in samples with different Yb3+ concentrations. Its value was found to be 90% for 3.8 and 10 at. %, 84% for 20 at. %, and 70% for 50 at. % Yb3+. The laser-emission tunability under diode pumping was found to extend from 1045 up to 1095 nm in a 12 at. % sample with 3.15 mm thickness.

Growth, spectroscopic, and laser properties of Yb 3+ -doped Lu 3 Al 5 O 12 garnet crystal

Two major fiber crystal growth methods have been applied for the synthesis and spectroscopic characterizations of Yb3+-doped Y3Al5O12 (Yb:YAG) to show the feasibility of a flexible single crystal fiber laser. One is the micropulling-down (μ-PD) method and the other is the laser heated pedestal growth (LHPG) method. 500 mm length fiber with no Yb segregation has been grown by the μ-PD method. A detailed analysis of Yb:YAG spectroscopy is made to contribute to the discussion on the determination of energy levels. On the other hand, a combinatorial chemistry approach has been applied on concentration gradient crystal fibers grown by the LHPG method allowing the measurement of the intrinsic radiative lifetime and the analysis of concentration quenching processes of Yb3+ ions in YAG.

Growth and spectroscopic analysis of Yb3+-doped Y3Al5O12 fiber single crystals

LuAlO/sub 3/:Ce/sup 3+/ (LuAP) and Lu/sub x/Y/sub 1/-xAlO/sub 3/:Ce/sup 3+/ (LuYAP) crystals are used as scintillation materials for positron emission tomography. The actual study of these scintillators develops in three directions: (i) growth of large size LuAP crystals with stable properties, (ii) the relationship between the composition of LuYAP crystals and scintillation properties, and (iii) scintillation mechanisms in lutetium compounds. After improving of growth conditions a large size samples (length >40 mm) have been prepared. Crystals show a good correlation between growth parameters, light yield and transmission spectra. We studied a series of samples with calibrated size (2/spl times/2/spl times/10 mm3) and compare the light yield with standard BGO and LSO samples. Mixed crystals with composition of 0.6<x<0.8 show a significant increase of light yield. We suggest that the short order clusterisation in mixed crystals may play an important role in governing the scintillation efficiency. In order to clarify the scintillation mechanism in LuAP and LuYAP crystals measurements of absorption, emission and excitation spectra, thermoluminescence and scintillation decay curves have been performed.

Progress in the development of LuAlO/sub 3/ based scintillators

Yb 3+ spectroscopic properties are given in garnet crystals. Especially, radiative energy transfer between Yb 3+ ions and non-radiative energy transfer between Yb 3+ and unexpected rare earth impurities are occurring as quenching mechanisms. Other mechanisms are also suspected from Yb 3+ pairs, OH- groups and even traces off Yb 2+ .

H. Canibano

Papers

Growth, spectroscopic, and laser properties of Yb 3+ -doped Lu 3 Al 5 O 12 garnet crystal

Growth and spectroscopic analysis of Yb3+-doped Y3Al5O12 fiber single crystals

Progress in the development of LuAlO/sub 3/ based scintillators

Spectroscopic properties and quenching mechanisms of Yb$^{3+}$- doped garnet crystals