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.

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LuAP:Ce and mixed LuYAP:Ce crystals are the promoted scintillation materials for positron emission tomography. These scintillators are presently being studied in three directions: 1) growth of large crystals with stable properties; 2) establishment of relationships between the composition of LuYAP:Ce crystals and the scintillation properties; and 3) scintillation mechanisms in lutetium compounds.We performed the first bunch of 16 LuYAP:Ce crystals with size for the detector module (2 2 10 mm 3 ). The crystals show good correlation among growth parameters, light yield, and transmission spectra. To clarify the scintillation mechanism in LuAP:Ce and LuYAP:Ce crystals, measurements of absorption, emission, and excitation spectra of thermoluminescence and scintillation decay curves have been performed.

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