Luminescence of Ba0.77Ca0.23TiO3 : Cr

Abstract

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 300-800nm spectral and 5-300K temperature region. Undoped BCT shows a fundamental optical absorption edge at similar to3.2 eV for light polarized along the tetragonal C-4 axis and at similar to 3.1 eV-normal to the C-4 axis at RT. Interband excitation with lambda(exc) = 350 nm results in a wide-band structured visible emission with broad peaks at similar to 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 A for T = 10 K. The shape of this line contains at least two well pronounced components A(1) at 7780 Angstrom, A(2) at 7740 Angstrom, and a weakly pronounced component A(1) at 7764 Angstrom, which are attributed to R-1 and R-2 emission lines (E-2 --> (4)A(2)) of octahedral Cr3+ without local charge compensation (A(1) and A(1)) and to another E-2 --> (4)A(2)transition with broad unresolved R'(1) and R'(2) lines (A(2)) belonging to another Cr3+ centre with charge compensation defect. Details of photoluminescence observed are considered in comparison with analogous data for Cr-doped BaTiO3, (C) 2003 Elsevier Science B.V. All rights reserved.