Optical absorption and luminescence spectroscopy of U{sup 3+} in K{sub 2}La{ital X}{sub 5} ({ital X}=Cl,Br,I)

Journal Article · Thu Aug 01 04:00:00 EDT 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.54.3830· OSTI ID:288185

Andres, H P; Kraemer, K; Guedel, H ^[1]

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1. Institut fuer Anorganische, Analytische and Physikalische Chemie, Freiestrae 3, CH-3000 Bern 9 (Switzerland)

The title compounds were synthesized and high-resolution absorption and luminescence spectra measured in the near-infrared, VIS, and near UV regions. The visible absorption spectra are dominated by very intense 5{ital f}{r_arrow}6{ital d} bands overlapping with {ital f}-{ital f} transitions. The onset of the first {ital f}-{ital d} absorption is shifted from 46000 cm{sup {minus}1} in K{sub 2}LaCl{sub 5}:Nd{sup 3+} to 15000 cm{sup {minus}1} in K{sub 2}LaCl{sub 5}:U{sup 3+}. Crystal-field splittings in corresponding {sup 2{ital S}+1}{ital L}{sub {ital J}} multiplets are greater by typically a factor of 2 in the U{sup 3+} doped crystal, thus reflecting the larger extension and stronger interaction of the 5{ital f} electrons with the ligands. {ital f}-{ital f} transitions are typically two orders of magnitude more intense in K{sub 2}LaCl{sub 5}:U{sup 3+} than in K{sub 2}LaCl{sub 5}:Nd{sup 3+}. Along the halide series K{sub 2}La{ital X}{sub 5}:U{sup 3+} ({ital X}=Cl,Br,I) the differences in the position of corresponding {ital f}-{ital d} and {ital f}-{ital f} transitions, crystal-field splittings, vibronic intensities, and excited-state lifetimes can be explained with the increasing covalency, the decreasing phonon energies, the increasing electron-phonon coupling, and the increasing U-{ital X} distances. The {ital f}-{ital d} excited states provide a nonradiative bypass of some {ital f}-{ital f} excited states in the case of all these halide lattices. The excited-state dynamics are determined by a delicate interplay of radiative and nonradiative relaxation processes, they are strongly dependent on the nature of {ital X}. Multiphonon relaxation processes are least competitive in the iodide due to the very low value of 106 cm{sup {minus}1} for the highest-energy phonons. A cross-relaxation mechanism determines the dynamics of the iodide at room temperature. {copyright} {ital 1996 The American Physical Society.}

• OSTI ID: 288185
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 6 Vol. 54; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ABSORPTION SPECTRA
AMBIENT TEMPERATURE
COVALENCE
CRYSTAL FIELD
D STATES
DOPED MATERIALS
ELECTRON-PHONON COUPLING
F STATES
LANTHANUM BORIDES
LANTHANUM CHLORIDES
LANTHANUM IODIDES
PHOTO-INDUCED TRANSIENT SPECTROSCOPY
PHOTOLUMINESCENCE
POTASSIUM BORIDES
POTASSIUM CHLORIDES
POTASSIUM IODIDES
UMKLAPP PROCESSES