Title
A photosensitive <tex>$Cr^{3+}$</tex> center in photorefractive <tex>$Bi_{12}SiO_{20}$</tex> crystals co-doped with chromium and phosphorus
Author
Faculty/Department
Faculty of Sciences. Physics
Publication type
article
Publication
New York, N.Y. :American Institute of Physics ,
Subject
Physics
Source (journal)
Journal of applied physics / American Institute of Physics. - New York, N.Y., 1937, currens
Volume/pages
109(2011) :8 , p. 083506,1-083506,7
ISSN
0021-8979
1089-7550
ISI
000290047000030
Carrier
E-only publicatie
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
A trigonal Cr3+ (3d3) defect in sillenite type Bi12SiO20 crystals co-doped with chromium and phosphorus has been identified by means of multi-frequency X-band (9.4 GHz), Q-band (35 GHz) and W-band (94 GHz) electron paramagnetic resonance (EPR). A consistent analysis of the observed spectra and their angular dependence was reached using an S = 3/2 spin Hamiltonian with axial symmetry around a &#12296;111&#12297; crystallographic direction, an isotropic g-value g = 1.983, and a zero field splitting parameter B20 = 0.1950 cm−1. The spectra are attributed to a chromium ion in the unusual Cr3+ valence replacing a substitutional Si4+ in tetrahedral oxygen coordination. Evidence is found that the symmetry lowering from tetrahedral to trigonal is not spontaneous but induced by an associated defect, for which a P5+ ion in a nearest-neighbor Si4+ site is the most plausible candidate. Optical excitation results in a reversible charge transfer process directly correlated with a photochromic effect: near-UV light leads to a strong reduction of the Cr3+ EPR signals, and induces a broad band at 675 nm in the absorption spectrum, and both effects are reversed under red light excitation.
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