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

Abstract

A nominal (Ba_1-x Ho _x )Ti_1-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 (Ba_1-x Ho_3x/4)(Ti_1-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.