Charge compensation and the luminescence of Cr3+ in KMgF3 |
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Authors: | D. R. Lee T. P. J. Han B. Henderson |
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Affiliation: | (1) Optical Materials Research Centre, Department of Physics and Applied Physics, University of Strathclyde, G1 1XN Glasgow, Scotland |
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Abstract: | Studies of the photoluminescence spectra of Cr3+ ions in KMgF3 crystals co-doped with Cr3+ and Ni2+ ions are reported. Several crystal field sites are identified by the different R-line spectra due to the 2E4A2 transition and broadband luminescences associated with the 4T24A2 transitions. Cr3+ ions substituting without local charge compensation on the octahedral Mg2+ site give rise to a low temperature R line in photoluminescence at =702.3 nm with a radiative decaytime of 3 ms at T=14 K. At T=300 K this isotropic centre gives rise to an unpolarized broadband 4T24A2 emission, which results from the thermal occupancy of an excited 4T2 state just above the 2E level which, at lower temperature, gives rise to emission in the R-line. Other crystal field sites are due to some Cr3+ ions having Mg2+ or K+ vacancies in nearest-neighbour positions, these vacancies being required to maintain charge neutrality in doped fluoride perovskites. The Cr3+–K+ vacancy complex results in the centre having trigonal symmetry, and low temperature, photoluminescence via R1 and R2 lines at 716.8 nm and 716.0 nm, respectively. Finally, Cr3+ ions having a nearest neighbour Mg2+ vacancy have tetragonal symmetry, experiencing weak crystal fields. In consequence, the 4T2 level lies below 2E and the photoluminescence spectrum at low temperature takes the form of a polarized broad 4T24A2 band with peak at 760 nm and radiative decaytime of 54 s. |
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Keywords: | 71.70.Ch 71.55.Ht |
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