CHROMIUM OPTICAL-SPECTRA AND STARK-EFFECT IN LIMBO(3)

The optical absorption, luminescence spectra and lifetime, Stark effec t in B ((4)A(2) -->T-2(2)) and R ((4)A(2) -->(2) E) transition regions of Cr3+ are examined in congruent and VTE stoichiometric LiNbO3:Cr3+. Narrow B-1 and B-2 lines at 5206 and 4931 Angstrom (T = 77 K) and six R1-6 lines in the 731-736 nm region are observed in absorption and em ission. Lifetime bf R-emission lines is about 268-295 mu s, ensuring t heir (E-2 -->(4)A(2)) origin. The R-lines width decreases about a fact or 2.5 in VTE specimens, in which the absence of R-6 emission at 7345 Angstrom is connected with a vanishing of unpaired Cr-Li(3+), when [Li ]/[Nb] ratio-increases. It is striking that at 10-80 K the inhomogeneo us broadened R-emission lines with temperature independent width appro ximate to 30 cm(-1), can be described by a Lorentz contour. At 77 K a large linear Stark effect was observed for absorption B- and R-lines w ith the same sign of Stark shift for R-lines. But B-1 and B-2 lines re veal a striking opposite Stark shift. No effect is detected for electr ic held applied normal to C-3 axes, ensuring C-3 position symmetry of the all optic Cr3+ centers observed.