试验优化设计Er3+/Yb3+共掺BaGd2ZnO5荧光粉及其上转换发光性质

为得到绿光和红光最大发光强度的Er³⁺/Yb³⁺共掺BaGd₂ZnO₅上转换材料荧光粉, 首先采用试验优化设计中的均匀设计初步寻找Er³⁺/Yb³⁺合理的掺杂浓度; 其次通过二次通用旋转组合设计进一步优化实验, 建立起Er³⁺/Yb³⁺掺杂浓度与绿光和红光发光强度的回归方程; 最后通过遗传算法计算出方程的最优解, 即绿光和红光最大发光强度时对应的Er³⁺/Yb³⁺掺杂浓度. 利用传统的高温固相法分别制备出最优样品. 采用X 射线衍射对得到荧光粉的晶体结构进行了分析, 证明了所有产物均为纯相BaGd₂ZnO₅. 采用980 nm抽运激光作为激发源, 在同样的条件下测量了样品的上转换荧光发射光谱, 从中可见样品有较强的红光发射和绿光发射, 发光中心位于662, 551和527 nm, 分别对应于⁴F_9/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 及²H_11/2→⁴I_15/2能级跃迁. 研究了绿光和红光最优样品的上转换发光强度与激光器工作电流之间的关系, 通过分析发现红色和绿色上转换发光均为双光子过程. 由归一化的绿色上转换发射光谱可以看出, 激光器工作电流导致的样品温度变化可以忽略不计. 由于能级²H_11/2和⁴S_3/2之间存在热平衡, 并满足玻尔兹曼分布, 由此探讨了绿光最优样品上转换发射光谱中的绿色发射与温度的关系, 计算出²H_11/2和⁴S_3/2之间的能级差为ΔE=926.11 cm^-1. 研究了绿光最优样品的温度效应, 随着温度的升高, 发射强度逐渐变小, 出现了温度猝灭现象. 并计算了样品的激活能, 分别为总体激活能ΔE_总=0.45 eV, 绿光激活能ΔE_绿=0.45 eV, 红光激活能ΔE_红=0.46 eV.

Experimental optimal design of the Er3+/Yb3+ codoped BaGd2ZnO5 phosphor and its upconversion luminescence properties

In order to obtain the Er³⁺/Yb³⁺ co-doped BaGd₂ZnO₅ up-conversion phosphor which has the maximum green and red emission intensity, firstly, the method of homogeneous design rooted in the experimental optimal design is employed to search optimum Er³⁺/Yb³⁺doping concentration preliminarily. Next, the quadratic general rotary unitized design is adopted to further optimize the experiment, and the regression equation in green and red emission intensity is established as a function of the doping concentration of Er³⁺/Yb³⁺. Finally, the optimal solution, that is, the doping concentration of Er³⁺/Yb³⁺ corresponding to the maximum emission intensity, is calculated by genetic algorithm. The optimal Er³⁺/Yb³⁺co-doped BaGd₂ZnO₅ phosphor is synthesized by the conventional high temperature solid state method. The crystal structure of as-prepared products is characterized by X-ray diffraction (XRD), and the results show that all the Er³⁺/Yb³⁺co-doped BaGd₂ZnO₅ phosphors we synthesized are of pure phase. The steady-state up-conversion (UC) emission spectra of products are measured under the excitation of a continuous 980 nm laser diode at different working currents. From the UC luminescent spectra of Er³⁺/Yb³⁺co-doped BaGd₂ZnO₅ phosphor, we can see a red emission centered at 662 nm, two green emissions centered at 551 nm and 527 nm, which are assigned to ⁴F_9/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ²H_11/2→$⁴I_15/2 transitions of Er³⁺ ion, respectively. The dependences of green and red UC emission intensities of optimal samples on working current are investigated, indicating that the red emission and green emission of optimal samples both originate from two-photon process. From the normalized green UC emission spectra, it can be concluded that the experimental laser working current induced temperature variation of samples can be omitted. According to Boltzmann distribution law and the thermal equilibrium existing between the levels of ²H_11/2 and ⁴S_3/2, the relationship between green emission and temperature in the optimal green UC emission sample is discussed in depth, and the energy level gap between ²H_11/2 level and ⁴S_3/2 level is calculated to be 926.11 cm^-1. Through the study of the temperature effect on the optimal green UC emission sample, we find that the emission intensity decreases with the increasing of the temperature, owing to the thermal quenching effect. Furthermore, we calculate the activation energies of the samples, the activation energies of the green emission, red emission, and the overall emission are deduced to be 0.45, 0.46, and 0.45 eV, respectively.