OPTICAL-SPECTRA OF BATIO3CR

Luminescence and optical absorption of Cr doped BaTiO3 were examined i n the 300-800 nm and 16.5-300 K region. Or doping results in additiona l absorption in the visible region, increasing towards the band edge ( at approximate to 400 nm) and in wide bands at 470, 575 and 610 nm. Sh arp emission lines peaking at 74 K at: 781.6 nm (A(1)), 776.4 nm (A(2) ), 768.8 nm (A(3)), and 766.8 nm (A(4)) were observed. Excitation spec tra of the A-lines look alike consisting in two broad complex bands at about 400 nm and 630 nm. The A-lines shift to higher energies with in creasing temperature with a shift coefficient of 0.04 to 0.12 cm(-1)/K . At 70 K A(1-4)-emission lifetime is approximate to 1 ms. We argue th at the A(3,4) lines correspond to zero-phonon E-2 --> (4)A(2) transiti ons of isolated Cr3+ ions replacing Ti4+. The nature of the A(1,2) emi ssion originate from Cr3+ exchange coupled with an unknown compensatin g defect (e.g., from Cr3+ pairs) or with E-2 --> A(2)-type transition of Cr3+, perturbed by nearest sited defects, e.g., by hole polaron (O- ) or OH-.