Photoluminescence associated with the site occupations of Ho3+ ions in BaTiO3.

A nominal (Ba1-x Ho x )Ti1-x/4O3 (x = 0.01) (BHTH) ceramic with a single-phase tetragonal structure was prepared at 1400 °C using the solid-state reaction method. The analysis on the defect chemistry revealed that the real formula of BHTH is (Ba1-x Ho3x/4)(Ti1-x/4Ho x/4)O3 with Ba vacancies via electron paramagnetic resonance (EPR). Photoluminescence (PL) was investigated on the basis of excitation with different wavelength lasers. The results indicated that under 488-nm excitation, PL and Raman scattering can occur simultaneously as two distinct optical processes for BHTH ceramic powders, and the strongest PL band at 564 nm was discovered and verified to originate from the 5G6/5F1 → 5I7 transition of Ho3+ ions on the Ti sites in the BaTiO3 lattice. Upon 532- and 638-nm excitations, three PL bands of 5F4/5S2 → 5I8, 5F5 → 5I8, and 5F4/5S2 → 5I7 transitions are attributed to the contributions from Ho3+ ions on the Ba sites. The common Raman spectrum of BaTiO3 can be observed without PL disturbance using 785-nm excitation wavelength. The PL effect may provide a probe for the site occupations of Ho3+ ions in widely-used BaTiO3 dielectric ceramics co-doped with Ho3+ and other dopants.