Luminescence of Ba0.77Ca0.23TiO3:Cr

Photoluminescence and optical absorption of nominally pure and Cr-doped (70–350 ppm) congruently melting Ba0.77Ca0.23TiO3 (BCT) single crystals were examined in the 300–800 nm spectral and 5–300 K temperature region. Undoped BCT shows a fundamental optical absorption edge at ∼3.2 eV for light polarized along the tetragonal C4 axis and at ∼3.1 eV—normal to the C4 axis at RT. Interband excitation with λexc=350 nm results in a wide-band structured visible emission with broad peaks at ∼655, 563, and 543 nm. Cr doping is accompanied by an additional absorption in the whole visible region, increasing towards the band edge and the appearance of strongly pronounced inhomogeneously broadened near IR emission line peaking at 7780 Å for T=10 K. The shape of this line contains at least two well pronounced components A1 at 7780 Å, A2 at 7740 Å, and a weakly pronounced component A′1 at 7764 Å, which are attributed to R1 and R2 emission lines (2E→4A2) of octahedral Cr3+ without local charge compensation (A1 and A′1) and to another 2E→4A2transition with broad unresolved R′1 and R′2 lines (A2) belonging to another Cr3+ centre with charge compensation defect. Details of photoluminescence observed are considered in comparison with analogous data for Cr-doped BaTiO3.