The role of disorder on Er³⁺ luminescence in Na_1/2Bi_1/2TiO₃

Photoluminescence in Er-doped NBT is studied at different temperatures. Remarkable reduction of the luminescence intensity in the green spectral range is found in the poled state comparing with the depoled state. Luminescence spectra at low temperatures reveal continuous wavelength shift of some maxima belonging to the ⁴S_3/2 → ⁴I_15/2 transition depending on the excitation wavelength, which is explained by large variety of different environments around Er³⁺ related to the random distribution of Na⁺ and Bi³⁺ in A-sublattice of the ABO₃ perovskite structure. Poling extends the wavelength range where shift of luminescence maxima is observed in the direction of longer excitation wavelengths. This feature can be explained by more ordered structure characteristic to the poled state comparing with the depoled one. Luminescence spectra of Er-doped BaTiO₃ are also measured at low temperatures, and confirm the role of Na⁺ and Bi³⁺ ion disorder in the observed spectral features of Er-doped NBT.