Correlation of crystal structure and optical properties of Ba_0.97Nd_0.0267Ti_(1-W O₃ perovskite

The Ba_0.97Nd_0.0267Ti_(1-W O₃ (BNT ) pervoskite with a single phase tetragonal structure was prepared at 900 °C using the Molten salt method. Raman spectra, Fourier transform infrared spectra (FT-IR), absorption spectra (Vis-NIR) and photoluminescence spectra (PL) in the temperature range from 10-300 K were used to investigate the correlations between the crystal structure and the optical properties of BNT ceramics. Raman analyses and FT-IR indicated that the W⁶⁺ ions are incorporated sufficiently into into the BNT lattice. The optical absorption spectra were recorded in the wavelength range of 400-1000 nm. The optical band gap (E _g) and Urbach energy (E _u) values were calculated from the absorption spectra. The emission spectra exhibited three prominent peaks located at 880, 1058 and 1340 nm corresponding to the ⁴F_3/2 → ⁴I_{9/2,11/2,13/2} transition levels, respectively. They also showed a decrease in the intensity of emission spectra following the addition of W⁶⁺ ions. This decrease is due to the slight changes in the crystal environment around Nd³⁺ and the non-radiative energy transfer. According to the PL measurements, the study of power-excitation density confirmed that two photons at low energy are required to create the down-conversion (DC) emissions, implying that they may also have important applications as DC materials.