YNbO4：Tm3+/Yb3+上转换发光特性研究

按照50Nb₂O₅-（46-x）Y₂O₃-4Yb₂O₃-xTm₂O₃（x=0.1，0.2，0.5，1，2）的配比方式，采用高温固相法制备出了掺杂Tm³⁺/Yb³⁺的YNbO₄晶体粉末。在980 nm红外光激发下，观测到波长为478，645，707 nm的上转换荧光，分别对应于Tm³⁺离子的¹G₄→³H₆、¹G₄→³F₄、³F₃→³H₆能级跃迁过程。利用上转换发射功率与980 nm激光器工作电流关系估算出跃迁过程吸收光子数目为2.72，2.69，2.01，从而确定出前两者为三光子吸收过程，最后一个对应于双光子吸收过程。运用Judd-Ofelt理论研究样品光谱特性，根据样品的吸收谱得到样品的谱线强度参数Ω_t（t=2，4，6），进而得出理论振子强度及实验振子强度，二者均方根偏差δ_rms=1.299×10^-7。计算了Tm³⁺离子向下能级跃迁的跃迁几率、跃迁分支比等参数。最后得出结论：（1）³F₄能级寿命较长，适合作为上转换中间能级；（2）³H₅能级寿命较长，且³H₅→³H₆跃迁分支比（96.46%）接近100%，可用于产生1 216 nm激光。

Up-conversion Luminescent Properties of YNbO4: Tm3+/Yb3+

Tm³⁺/Yb³⁺ droped YNbO₄ power sample was prepared with the molar ratios of 50Nb₂O₅-(46-x)Y₂O₃-4Yb₂O₃-xTm₂O₃ (x=0.1, 0.2, 0.5, 1, 2) by the high temperature solid state method at 1 300℃. Under 980 nm laser excitation, the upconversion luminescence spectra of samples show 478 nm from ¹G₄→³H₆ transition of Tm³⁺ ions, 645 nm attributed to ¹G₄→³F₄ transition of Tm³⁺ ions, respectively, and 707 nm emissions assigned to ³F₃→³H₆ transition of Tm³⁺ ions. The transition process is estimated by using the relation between the upconversion power and the operating current of the 980 nm laser. The numbers of photons absorbed are 2.72, 2.69 and 2.01. The first two correspond to three-photon absorption processes, and the last one corresponds to two-photon absorption process. The spectral properties of the samples are studied by using Judd-Ofelt theory. Spectral strength parameters Ω_t(t=2,4,6) were computed based on the absorption peak's area of the absorption spectrum. The theoretical oscillator strength and the experimental oscillator strength were calculated according to the spectrum strength parameters,and the root mean square deviation (δ_rms) was 1.299×10^-7. The transition probability, branching ratio and other parameters of the lower level transition of Tm³⁺ ion were calculated. The results show that:(1) the ³F₄ has a longer level lifetime, which is suitable for up-conversion intermediate level; (2)³H₅ has a longer level lifetime, and the transition branching ratio of ³H₅→³H₆ is close to 100%(96.46%), so this sample can be used to generate 1 216 nm laser.