Tm~(3+)/Yb~(3+)∶LaF_3纳米体系中掺杂Yb~(3+)离子对Tm~(3+)离子荧光发射的影响

为研究Yb~(3+)离子浓度变化对Tm~(3+)离子在蓝色波段荧光强度的影响,以NaF和La(NO_3)_3为原料,采用水热法制备了Tm~(3+)和Yb~(3+)共掺的Tm~(3+)/ Yb~(3+)∶LaF_3纳米颗粒.用X射线衍射对LaF_3纳米颗粒进行表征的结果显示,纳米晶体结构呈六方相.透射电镜的观测结果显示,纳米颗粒样品大小均匀、分散性良好.在波长为800 nm的激光激发下,观测到了上转换蓝光发射,其中包括波长为474 nm和479 nm的较强的荧光辐射(相应的跃迁为~1G_4→~3H_6)和波长位于450 nm的强度较弱的荧光发射(相应的跃迁为~1D_2→~3F_4).通过观测不同Yb~(3+)离子浓度条件下共掺Tm~(3+)/Yb~(3+)∶LaF_3样品的荧光光谱,研究了Yb~(3+)离子掺杂浓度对于Tm~(3+)离子的荧光发射的影响,并探讨了产生这种现象的原因.研究结果显示,对于~1G_4→~3H_6跃迁产生的荧光发射(474 nm),当Yb~(3+)离子浓度增大时,反向能量传递速率的增加导致了荧光强度的增大.然而,当Yb~(3+)离子浓度增大到一定程度时,Yb~(3+)离子激发态能级寿命的减少将引发荧光强度的下降.相比较而言,Yb~(3+)离子的浓度的变化对于~1D_2→~3F_4跃迁产生的位于450 nm处荧光强度的影响较弱.

Influence of Yb~(3+) Concentration on the Fluorescence Emission of Tm~(3+) in Tm~(3+) /Yb~(3+):LaF_3 Nanoparticals

In order to investigate the influence of Yb~(3+)concentration on the up-converted blue fluorescence intensity of Tm~(3+) ions,the fluorescent materials of Tm~(3+) and Yb~(3+) codoped LaF_3 nanoparticles are prepared using hydrothermal method with NaF and La(NO_3)_3 as raw materials.The result of X-ray diffraction shows that the crystal structure of the prepared nanoparticles is hexagonal.The image of the transmission electron microscopy suggents that the particles are uniformly distributed and have a good dispersity.Up-converted blue emissions at 474 nm and 450 nm,which correspond to the transitions of ~1G_4→~3H_6 and ~1D_2→~3F_4 respectively,are observed when the samples are excited with 800 nm lasers.The influence of Yb~(3+) concentration on the fluorescence properties of Tm~(3+) ions is investigated by adjusting the Yb~(3+) concentration in Tm~(3+)/Yb~(3+):LaF_3 nanoparticles.It is found that for fluorescence emission at 474 nm,when the concentration of the Yb~(3+) increases,the fluorescence intensity also increases due to inverse energy transfer process.But the fluorescence intensity will decrease after it reaches a certain value.For the fluorescence emission at 450 nm,its intensity does not change obviously with the concentration of Yb~(3+) ions,but its fluorescence intensity is increasing firstly and then decrease like 474 nm fluorescence.