Abstract: Orthorhombic phase α-BiNbO₄∶Eu³⁺ and triclinic phase β-BiNbO₄∶Eu³⁺ were synthesized by solid-state reaction method. Their structure and fluorescence properties were studied by X-ray diffractometer (XRD), Raman spectra, absorption spectra and luminescence spectra. Results indicate that pure α-BiNbO₄ were successfully synthesized at 900 ℃, while triclinic phase β-BiNbO₄ obtained at 1 200 ℃. The band structure of both structure BiNbO₄ was studied using the first principle theory and absorption spectra. The optical band gap obtained for α-BiNbO₄ and β-BiNbO₄ are 2.69 eV and 2.96 eV respectively, in agreement with the theoretical result of 2.640 eV and 3.032 eV. After Eu³⁺ doping, theirs band gap blue shifts to 2.89 eV and 3.05 eV respectively, which effectively change their optical response range. The main emission peaks are from ⁵D₀→⁷F₂ transition of Eu³⁺ for both structural BiNbO₄∶Eu, centerted at 615 nm and 611 nm respectively. But the emission intensity of β-BiNbO₄∶Eu sample is much higher, and its luminescence intensity ratio between ⁵D₀→⁷F₂ and ⁵D₀→⁷F₁ transitions is much higher. For Er³⁺ doping, upconversion emission is observed for both structures excited at 980 nm. The upconversion emission intensity of β-BiNbO₄∶Er sample is almost 40 times higher than that of α-BiNbO₄∶Er sample. This results indicate that β-BiNbO₄ is more suitable as the host material of rare earth ions doping phosphor.

Key words: luminescence material, BiNbO₄, Eu doping, fluorescence spectrum, Raman spectrum, first-principle theory, optical response, absorption property