Fluorescence Properties of α- and β-BiNbO4:Eu³⁺. (English)

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 °C, while triclinic phase β-BiNbO4 obtained at 1 200 °C. 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. [ABSTRACT FROM AUTHOR]

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