C. Fischer et al., SHARP R-LINES IN ABSORPTION AND EMISSION OF CR3+ IN STOICHIOMETRIC (VTE) LINBO3, Radiation effects and defects in solids, 135(1-4), 1995, pp. 697-700
R-line absorption and luminescence spectra of Cr3+ doped LiNbO3 show a
distinct dependence on crystal stoichiometry. In the Cr3+ R-line regi
on around 730 nm, up to five transitions can be observed in absorption
and emission. In stoichiometric LiNbO3:Cr crystals the line width (FW
HM) in both absorption and emission decreases by about a factor of 2.5
in comparison with the same transitions in congruent samples. The emi
ssion line at lowest energy in the R-line spectrum (lambda = 734.5 nm)
disappears completely in stoichiometric LiNbO3:Cr. This results, disc
ussed together with models dealing with charge compensated Cr3+ pairs
on Li and Nb sites and unpaired Cr3+ on Li site, is indicating a vanis
hing of the unpaired Cr-Li(3+) with increasing [Li]/[Nb] ratio. Lumine
scence lifetime measurements in stoichiometric LiNbO3:Cr reveal values
similar to results for congruent material of tau = 295 mu s for the 7
31 nm line and tau = 268 mu s for the 735 nm line, underlining the R-l
ine character of these transitions.