不同掺杂浓度Tm3+：LiLuF4单晶的1800 nm荧光发射

采用坩埚下降法生长了Tm³⁺掺杂浓度为0.45%，0.90%，1.63%与3.25%（摩尔分数，x）的LiLuF₄单晶.测试了样品的电感耦合等离子体原子发射光谱（ICP-AES）、X射线衍射（XRD）谱、吸收光谱（1400-2000 nm），并且分析比较了808 nm半导体激光器（LD）激发下荧光光谱. 结果表明：当Tm³⁺的浓度从0.45%变化到3.25%时，1800 nm处的荧光强度呈现了先增后减的趋势，当掺杂浓度约为0.90%时达到最大值，而位于1470 nm处的荧光强度则呈现了相反的趋势. Tm³⁺：³F₄能级的荧光衰减寿命随着掺杂浓度的增加不断减小. 1800 nm处的这种荧光强度变化归结于Tm³⁺离子间的交叉驰豫效应（³H₆，³H₄→³F₄，³F₄）和自身的浓度猝灭效应. 同时计算得到了浓度为0.90%的样品在1890 nm处的最大发射截面为0.392×10^-20 cm². 并且根据Judd-Ofelt 理论所得寿命和测定的荧光寿命计算得到了³F₄→³H₆的最大量子效率约为120%.

Fluorescent Emissions (1800 nm) of LiLuF4 Single Crystals Doped with Various Tm3+ Concentrations

LiLuF₄ single crystals doped with molar fractions of 0.45%, 0.90%, 1.63%, and 3.25% (x, molar fraction) Tm³⁺ ions were fabricated by an improved Bridgman method. Absorption spectra in the 400-2000 nm region of the crystals were measured. The emissions from 1400 to 2000 nm under excitation of an 808-nm laser diode (LD) were carried out and compared. Two emission bands at 1470 and 1800 nm were observed. First, the emission intensity at 1800 nm increased with the increase in Tm³⁺ concentration, reaching a maximum value when the Tm³⁺ concentration was ca 0.90%. Thereafter, it decreased considerably as the Tm³⁺ doping levels further increased to 3.25%. However, the emission intensity at 1470 nm showed the contrary tendency to that at 1800 nm. It was found that the 1800-nm emission lifetime of the Tm³⁺:³F₄ manifold systematically decreased with an increase in Tm³⁺ concentration. The trend in the fluorescent intensity change can be explained by the cross-relaxation (³H₆, ³H₄→³F₄, ³F₄) between the Tm³⁺ ions and the concentration quenching effect of Tm³⁺. Meanwhile, the emission cross-section was calculated, providing a maximum of 0.392×10^-20 cm² at 1890 nm for the 0.90% doped sample. Based on the measured lifetime and calculated radiative lifetime, the largest quantum efficiency between Tm³⁺ ions reached ~120%.