The absorption and fluorescence spectra of Eu3+ in LaCl3 were obtained and analyzed. Crystal-field calculations give good agreement with the observed Stark components for B20 = A20〈r2〉 = 89 cm—1, B40 = —38 cm—1, B60 = —51 cm—1, and B66 = 495 cm—1.
The Judd-Ofelt (JO) theory was applied to optical-absorption transitions in Nd+3 : YVO4 to obtain intensity parameters (Ω2=5.88×10−20 cm2; Ω4=4.08×10−20 cm2; Ω6=5.11×10−20 cm2) and the radiative lifetime (152 μs) and quantum efficiency (0.72) of the 4F3/2 state. The variations of the absorptions with respect to the optic axis measured for Nd+3 in a uniaxial crystal were taken into account in applying the JO theory. In addition, transition-matrix elements using new intermediate-coupling coefficients were obtained and used in the JO fitting procedure.
Laser action at 530 nm using H3 centers in diamond was observed with an efficiency of 13.5% at room temperature. Optical double-resonance experiments on N3 centers provided direct evidence for a 2 A metastable level. Its presence results in rapid decay of the excited 2 E state and low quantum efficiency as well as significant excited-state absorption in the N3 luminescence region.Since the pioneering spectroscopy on FA (II) centers in KCl by Fritz et al. ,1 which led to construction of the first color-center laser by Fritz and Menke, 2 many efficient, widely tunable sources of coherent radiation based on defect structures in alkali halides have been developed.
3These ionic crystals have hitherto required cooling to cryogenic temperatures, however, both to prolong the shelf-life of laser-active centers and to achieve high quantum efficiency. While stable, tunable laser operation and Q switching using F-aggregate centers in LiF at room temperature have been achieved recently with special techniques, 4 in the work reported in this Letter we have followed a different approach to secure hightemperature operation. We have investigated substitutional impurities in a covalent crystal and have obtained efficient, visible laser action using H3 centers in diamond at room temperature. Diamonds contain a variety of color centers owing to the presence of impurity atom and vacancy complexes.
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