We are engaged in a systematic study of the optical and laser properties of Cr 2ϩ -doped cadmium chalcogenides. Previously, we demonstrated quasi-continuous wave lasing from Cr 2ϩ -doped Cd 0.55 Mn 0.45 Te with slope efficiencies as high as 64% and a laser tuning range from 2,170-3,010 nm. In this paper, we report the first demonstration of lasing from Cr:CdTe at room temperature. Pulsed-laser operation was obtained with a free-running spectrum centered at 2,535 nm. The slope efficiency of the laser was low (ϳ1%) because of large parasitic losses at the laser wavelength. The spectroscopic properties of Cr:CdTe are favorable for laser applications because of a large emission cross section (ϳ2.5 ϫ 10 Ϫ18 cm 2 ) and a high emission-quantum yield (ϳ88%). In addition, CdTe can easily incorporate Cr ions either through melt growth or diffusion doping. Along with our results on Cr 2ϩ :CdTe, we report on the optical properties of several other Cr 2ϩ -doped II-VI semiconductors (ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, Cd 0.9 Zn 0.1 Te, Cd 0.65 Mg 0.35 Te, Cd 0.85 Mn 0.15 Te, and Cd 0.55 Mn 0.45 Te) and compare them for applications as solid-state laser materials.

Results of the spectroscopic characteristics and upconversion luminescence in Er 3+ doped yttria (Y 2 O 3 ) transparent ceramics prepared by a modified two-step sintering method are presented. The near-infrared (1.5 lm) luminescence properties were evaluated as a function of Er 3+ concentration. Judd-Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er 3+ -doped Y 2 O 3 single crystal and nanocrystals. Following pumping at 1.532 lm, weak blue (~0.41 lm, 2 H 9/2 ? 4 I 15/2 ), strong green (~0.56 lm, 2 H 11/2 , 4 S 3/2 ? 4 I 15/2 ), and red (~0.67 lm, 4 F 9/2 ? 4 I 15/2 ) emission bands were observed as well as weak near-infrared emissions at 0.8 lm ( 4 I 9/2 ? 4 I 15/2 ) and 0.85 lm ( 4 S 3/2 ? 4 I 13/2 ) at room temperature. The upconversion luminescence properties under 1.5 lm pumping were further investigated through pump power dependence and decay time studies. Sequential twophoton absorption leads to the 4 I 9/2 upconversion emission, whereas energy-transfer upconversion is responsible for the emission from the higher excited states 2 H 9/2 , 2 H 11/2 , 4 S 3/2 , and 4 F 9/2 . The enhanced red emission with increasing Er 3+ concentration most likely occurred via the cross-relaxation process between ( 4 F 7/2 ? 4 F 9/2 ) and ( 4 I 11/2 ? 4 F 9/2 ) transitions, which increased the population of the 4 F 9/2 level. 2105

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