α相和β相BiNbO4∶Eu3+的荧光性能

采用高温固相法合成出正交相和三斜相结构的BiNbO₄∶Eu³⁺样品,利用X 射线衍射(XRD)、拉曼光谱、吸收光谱和荧光光谱对样品的结构和光学性能进行了研究。结果表明:900 ℃合成样品为正交相结构α-BiNbO₄,而1 200 ℃得到三斜相结构β-BiNbO₄。吸收光谱得到α相和β相BiNbO₄的光学带隙分别为2.69 eV和2.96 eV,与第一性原理的理论结果2.640 eV和3.032 eV相吻合。Eu³⁺掺杂诱导二者的光学带隙蓝移至2.89 eV和3.05 eV,有效改变了其光响应范围。荧光光谱表明:Eu³⁺在两种结构的最强荧光峰均来自⁵D₀→⁷F₂电偶极跃迁,最强荧光峰分别位于615 nm和611 nm。Eu³⁺在β-BiNbO₄中的荧光强度更高,而且其⁵D₀→⁷F₂和⁵D₀→⁷F₁的荧光强度比值更大。与Eu³⁺相似,Er³⁺在β-BiNbO₄中具有更高的上转换荧光强度,其强度约是在α-BiNbO₄中荧光的近40倍,说明三斜结构BiNbO₄更适合做稀土离子的基质材料。

Fluorescence Properties of α- and β-BiNbO4∶Eu3+

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.