Relative halide-concentration dependence of the F-centre optical absorption properties in KClxBr(1-x):Eu2+ crystals: Influence of Eu2+-cation vacancy dipoles
Por:
Cordero-Borboa A.E., Flores C.J., Hernández J.A., Aguilar G.S., Murrieta H.
Publicada:
1 ene 2005
Resumen:
The influence of Eu2+-cation vacancy (I- V) dipoles on the relative halide-concentration dependence of the F-centre optical absorption properties in KClxBr(1-x):Eu2+ crystals has been investigated. These crystals are made of a single mixed face-centred cubic (FCC)-phase whose unit-cell size a0 obeys the Vegard's rule, and their optical absorption spectrum consists of a single F-band whose spectral width depends on x, reaching 0.414 ± 0.006eV at x = 0.5, and whose spectral frequency ?m and equivalent energy ?m satisfy the equations ?m a0 2.24±0.09 =26 ± 2 and ?m (eV) = (0.06 ± 0.01)x2 + (0.16 ± 0.01)x + (1.98 ± 0.01). Comparison with the F-centre optical absorption properties reported elsewhere for pure FCC alkali-halide and KClxBr(1-x) crystals showed that in KClxBr (1-x):Eu2+ crystals, the alkali and halide ion sizes drive mainly the F-band spectral position, and also that this position is more sensitive to changes in a0 in KClxBr(1-x): Eu2+ crystals than in pure FCC alkalihalides. This is due to the crystalline electric field distortion caused locally at the F-centre by the mixed halide surroundings. This distortion affected the F-band spectral position in KClxBr(1-x):Eu2+ crystals to a lesser extent than it did in KClxBr(1-x) crystals. This might be due to the presence of I-V dipoles.
Filiaciones:
Cordero-Borboa A.E.:
Instituto de Física, UNAM, A.P. 20-364, D.A. Obregon, Mexico D.F. 01000, Mexico
Flores C.J.:
Instituto de Física, UNAM, A.P. 20-364, D.A. Obregon, Mexico D.F. 01000, Mexico
Hernández J.A.:
Instituto de Física, UNAM, A.P. 20-364, D.A. Obregon, Mexico D.F. 01000, Mexico
Aguilar G.S.:
Instituto de Investigaciones en Materiales, UNAM, 70-360, México D.F. 04510, Mexico
Murrieta H.:
Instituto de Física, UNAM, A.P. 20-364, D.A. Obregon, Mexico D.F. 01000, Mexico
|