通过化学溶液沉积法制备了 Er³⁺-Tm³⁺-Yb³⁺ 共掺杂的Bi₄Ti₃O₁₂薄膜, 并研究了薄膜的上转换荧光和铁电性能. 在980 nm红外光的激发下, 薄膜的室温发射光谱在可见光区域显示出4个发射带, 分别是峰值为478 nm的蓝光发射带, 对应Tm³⁺的 ¹G₄→³H₆能级跃迁; 峰值为527和548 nm的绿光发射带, 对应 Er³⁺ 的 ²H_11/2 → ⁴I_15/2 和 ⁴S_3/2 → ⁴I_15/2 能级跃迁; 峰值为 657 nm 的红光发射带, 由 Er³⁺ 的 ⁴F_9/2 → ⁴I_15/2 和 Tm³⁺ 的 ¹G₄ → ³F₄能级跃迁产生的发射带复合而成. 荧光的颜色可以通过改变Er³⁺, Tm³⁺, Yb³⁺ 离子的掺杂浓度加以调节. 在固定Tm³⁺, Yb³⁺ 浓度的Bi_3.59-xEr_xTm_0.01Yb_0.4Ti₃O₁₂(BEr_xTYT) 薄膜中, 随着Er³⁺浓度的增加, 红、蓝光和绿、蓝光的强度比均增加, Er³⁺离子的淬灭浓度为 1.75‰(摩尔分数, 下同); 在固定 Er³⁺, Yb³⁺ 浓度的Bi_3.593-yEr_0.007Tm_yYb_0.4Ti₃O₁₂(BETm_yYT) 薄膜中, 随着Tm³⁺ 浓度的增加, 绿、蓝光和红、蓝光的强度比均降低, Tm³⁺ 的淬灭浓度为 2.5‰; 在固定 Er³⁺, Tm³⁺ 浓度的Bi_3.98-zEr_0.01Tm_0.01Yb_zTi₃O₁₂(BETYb_zT) 薄膜中, 随着 Yb³⁺ 浓度的增加, 蓝、绿光和红、绿光的强度比均增加, Yb³⁺ 对 Er³⁺ 发射的荧光淬灭浓度小于5%, 而对 Tm³⁺ 发射的荧光淬灭浓度大于 18%. Bi_3.5815Er_0.0085Tm_0.01Yb_0.4Ti₃O₁₂ 薄膜上转换荧光值为(0.31, 0.34), 最接近标准白光的色度坐标(0.33, 0.33). 在不同功率的红外激光激发下, 薄膜荧光的色度坐标变化幅度很小, 说明薄膜具有较好的颜色稳定性. 通过分析薄膜荧光的上转换机制, 从 Er³⁺ 向 Tm³⁺ 有明显的能量传递发生, 使光谱中红、绿、蓝光的相对强度和稀土离子的淬灭浓度发生明显变化. 薄膜的铁电性能测试表明, 当 Er³⁺, Tm³⁺, Yb³⁺ 掺杂的总浓度约为 10% 时(Bi_3.5815Er_0.0085Tm_0.01Yb_0.4Ti₃O₁₂), 薄膜的铁电剩余极化强度达到最大值, 为 27.8 μC/cm².

The Er³⁺-Tm³⁺-Yb³⁺ tri-codoped Bi₄Ti₃O₁₂ thin films were prepared by chemical solution deposition method and its upconversion (UC) photoluminescence and ferroelectric properties were studied. There are four emission bands in the visible UC luminescence spectra excited by 980 nm infrared light at room temperature. The 478 nm blue emission band corresponds to ¹G₄ → ³H₆ transition of Tm³⁺, and the 527, 548 nm green emission bands correspond to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺, and the 657 nm red emission band corresponds to ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺ and ¹G₄ → ³F₄ transition of Tm³⁺. The fluorescent color can be tuned by adjusting Er³⁺, Tm³⁺ and Yb³⁺ concentrations. For Bi_3.59-xEr_xTm_0.01Yb_0.4Ti₃O₁₂ (BEr_xTYT) thin films with fixed Tm³⁺ and Yb³⁺ concentrations, the intensity ratio of green and red emissions to blue one gradually increased with the increase of Er³⁺ concentrations, and the quenching concentration of Er³⁺ is only about 1.75‰ (mole fraction). For Bi_3.593-yEr_0.007Tm_yYb_0.4Ti₃O₁₂ (BETm_yYT) thin films with fixed Er³⁺ and Yb³⁺ concentrations, the intensity ratio of green and red emissions to blue one decreased with the increase of Tm³⁺ concentrations, and Tm³⁺ quenching concentration is about 2.5‰. For Bi_3.98-zEr_0.01Tm_0.01Yb_zTi₃O₁₂ (BETYb_zT) thin films with fixed Er³⁺ and Tm³⁺ concentrations, the intensity ratio of blue or red emission to green one increase with increase of Yb³⁺ concentrations, and Yb³⁺ quenching concentration is less than 5 mol% for the luminescence from Er³⁺ and lager than 18 mol% for the luminescence from Tm³⁺. The optimal color coordinate in these films is (0.31, 0.34), close to standard white-light coordinate of (0.33, 0.33), which appears in Bi_3.5815Er_0.0085Tm_0.01Yb_0.4Ti₃O₁₂ thin film. The color coordinate has only a little change with increasing pumping power, which suggests that luminescence from the thin films has good color stability. There exist significant energy transfers from Er³⁺ to Tm³⁺, which will affect the relative intensities of blue, green and red emissions and their quenching concentrations by analyzing the UC emission mechanism of the thin films. The remnant polarization value of the film prepared on Pt/Ti/SiO₂/Si substrate reaches the maximum and is equal to 27.8 μC/cm² when the total codoping concentration of Er³⁺, Tm³⁺ and Yb³⁺ is about 10% (Bi_3.5815Er_0.0085Tm_0.01Yb_0.4Ti₃O₁₂ film).