在NaGdF4：Tm3+, Dy3+中Gd3+间的能量迁移及Gd3+-Dy3+能量传递量子效率

基于量子剪裁基本原理,通过光谱技术研究NaGdF₄:Tm³⁺,Dy³⁺在一个真空紫外光子激发下获得两个蓝色光子的可能性。在这种化合物中,量子剪裁通过下转换,即通过应用不同镧系离子间的能量传递进行。通过对Tm 4f¹²-4f¹¹5d激发,部分能量从Tm³⁺离子5d态直接传递给Gd³⁺,然后在Gd³⁺-Tm³⁺之间发生交叉弛豫,剩余能量从Gd³⁺传递给Dy³⁺,产生两个可见光子发射,一个来自Tm³⁺的¹G₄-³H₆跃迁,另一个来自Dy³⁺的⁴F_9/2-⁶H_15/2跃迁。主要研究获得以NaGdF₄:Tm³⁺,Dy³⁺为基础的新型具有更高效率,更高稳定性和更强真空紫外(VUV)吸收量子剪裁发光粉的可能性。各种光谱技术,如光致发光、激发和衰减等被用来表征不同Dy³⁺浓度掺杂NaGdF₄中Gd³⁺晶格间能量迁移引起的施主Gd³⁺和受主Dy³⁺之间的能量传递。结果表明Gd³⁺离子之间存在能量迁移,随之交换相互作用引起施主与受主(Gd³⁺-Dy³⁺)之间的能量传递。通过Bursh-tein等人关于激发态的弛豫理论,施主-受主能量传递参数k_DS可以从Gd³⁺的⁶P_7/2发射的衰减计算出。Gd³⁺-Dy³⁺能量传递量子效率也可以得到。NaGdF₄:Tm³⁺和NaGdF₄:Tm³⁺,Dy³⁺是由水热法制备的,NaGdF₄:Dy³⁺是由文献4]方法制备的。发射光谱和激发光谱通过自制的VUV光谱仪和F-4500测量。衰减曲线由OPO激光器激发获得Gd³⁺-Dy³⁺之间能量传递量子效率在受主浓度大约在N_A=0.6%时达到最佳值,并且明显地观测到浓度猝灭效应。

Energy Migration Among Gd3+ and Quantum Efficiencies of Gd3+-Dy3+ Energy Transfer in NaGdF4:Tm3+,Dy3+

The possibility to obtain two blue photons under excitation of one VUV photon in NaGdF₄:Tm³⁺,Dy³⁺ has been investigated by means of spectroscopic techniques,based on quantum cutting principle.In this compound visible quantum cutting is achieved through downconversion,i.e.,by making use of energy transfer between different lanthanide ions.Upon VUV excitation in the 4f¹⁰5d levels of Tm³⁺,part of the energy is transferred directly from the Tm³⁺ 4f¹⁰5d states to Gd³⁺.The cross-relaxation between Gd³⁺-Tm³⁺ is followed,and then the left energy is transferred from Gd³⁺ to Dy³⁺.Two visible photons are yielded:one from Tm³⁺ due to ¹G₄→³H₆ transition,and one from Dy³⁺ due to ⁴F_9/2→⁶H_15/2 transition.In this paper,the possibility to obtain a new quantum cutting phosphor with higher efficiency,higher stability and higher VUV absorption based on NaGdF₄:Tm³⁺,Dy³⁺ has been investigated.The spectroscopic techniques,including luminescent emission,excitation,decay,etc.were performed to characterize the donor Gd³⁺ ion-acceptor Dy³⁺ ion energy transfer preceded by energy migration among Gd³⁺ lattices in NaGdF₄ doped with different concentrations of Dy³⁺ ions.It is shown by the results that the Gd³⁺-Dy³⁺ transfer preceded by energy migration among the Gd³⁺ ions is mainly governed by the exchange interaction.By the theory on excited state relaxation processes,which was developed by Burshtein et al.,the donor-acceptor energy transfer parameter kDA can be calculated from the ⁶P_7/2 emission decay of Gd³⁺.The quantum efficiency of Gd³⁺-Dy³⁺ energy transfer was derived as well.Powders of NaGdF₄:Tm³⁺(1.5%) and NaGdF₄:Tm³⁺(1.5%),Dy³⁺(0.3%) were prepared by the hydrothermal technique,and NaGdF₄:Dy³⁺(0.3%,0.6%,1%,3% and 5 %) by the method described in Ref.4].The emission and excitation spectra were measured by home-made VUV spectrometer and F4500 monochromator.The decay curves were obtained under excitation of OPO laser.The quantum efficiencies for the Gd³⁺-Dy³⁺ energy transfer have an optimal value for acceptor concentrations at about N_A=0.6% and concentration quenching can be observed obviously.