A photosensitive Cr3+ center in photorefractive Bi12SiO20 crystals co-doped with chromium and phosphorus

作者：Ahmad Ijaz^*; Marinova Vera; Vrielinck Henk; Callens Freddy; Goovaerts Etienne

来源：Journal of Applied Physics, 2011, 109(8): 083506.

DOI：10.1063/1.3561503

A trigonal Cr3+(3d(3)) 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 < 111 > crystallographic direction, an isotropic g-value g = 1.983, and a zero field splitting parameter B-2(0) = 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.

• 出版日期2011-4-15