Spectroscopic properties of alexandrite crystals II |
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| Institution: | 1. Department of Materials Science, Sichuan University, 610064 Chengdu, China;2. Southwest Institute of Technical Physics, Chengdu 610041, China;1. Promising Centre for Sensors and Electronic Devices (PCSED), Advanced Materials and Nano-Research Centre, Najran University, P.O. Box: 1988, Najran 11001, Saudi Arabia;2. Nanostructured Materials and Nanotechnology Division, Central Metallurgical Research and Development Institute (CMRDI), P.O. Box: 87, Helwan, Cairo 11421, Egypt;3. College of Science and Arts-Sharoura, Najran University, Saudi Arabia;4. Department of Physics, College of Science and Arts, Najran University, P.O. Box: 1988, Najran 11001, Saudi Arabia;1. Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, A-6020 Innsbruck, Austria;2. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Department of Crystallography, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany;1. Electron Microscope Unit, University of the Western Cape, Robert Sobukwe Drive, Bellville 7535, South Africa;2. Physics Department, University of the Western Cape, Robert Sobukwe Drive, Bellville 7535, South Africa |
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| Abstract: | Several aspects of the optical spectroscopic properties of alexandrite crystals not previously investigated are reported here. For Cr3+ ions occupying the Al3+ lattice sites with mirror symmetry in BeAl2O4, the positions of the zero-phonon lines for absorption transitions to the 2T1g and 4T2g levels are identified, and vibronic transition peaks in the fluorescence spectrum are compared to transitions appearing in the Raman spectrum and Stokes excitation spectrum. In addition, the effects of radiation trapping are shown to lengthen the fluorescence lifetime of the 2Eg - 4A2g transition for ions in these sites at low temperatures. For Cr3+ ions occupying the Al3+ lattice with inversion symmetry, the ground state splitting of the 2Eg - 4A2g transition is reported and the decrease of the fluorescence lifetime with temperature is shown to be due to the increase in vibronic emission probability as well as increased probability of direct radiationless decay. |
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