基质材料对Yb~(3+)浓度调控的上转换荧光红绿比的影响

控制Yb~(3+)掺杂浓度是一种重要的调控红绿荧光比率的方法.然而,关于不同基质中Yb~(3+)浓度对红绿上转换荧光调控的敏感度仍缺少定量的对比研究,而且调控机理尚不清晰.本文通过乙二胺四乙酸辅助的水热法,合成了形貌可控的NaYF_4微米棒、LiYF_4微米八面体和YF_3微米砖三种氟化物晶体.通过激光共聚焦显微镜系统对比研究了Yb~(3+)/Er~(3+)掺杂的三种不同基质和形貌的单颗粒氟化物微米晶体的上转换荧光行为和红绿比率对Yb~(3+)变化的敏感度.研究结果表明:NaYF_4:Er~(3+)微米棒的红绿比率对Yb~(3+)的掺杂浓度响应最为敏感,各种Yb~(3+)浓度掺杂的LiYF_4:Er~(3+)微米八面体上转换荧光被绿光主控,而不同Yb~(3+)掺杂的YF_3:Er~(3+)微米砖表现出了稳定的黄光发射.通过分析荧光发射谱和比较上下转换荧光动力学过程结合荧光强度-功率依赖关系,基于拥有不同声子能量的基质辅助的Er~(3+)离子中间态的不同消布居途径,揭示了不同基质中红绿比率对Yb~(3+)变化响应的物理机制,并提供了一种研究上转换机理的思路.

Effect of host matrix on Yb3+ concentration controlled red to green luminescence ratio

Rare earth doped upconverting micro/nanoparticles with controlled size and structure,which are excited by near-infrared light and emit the visible light,possess many applications especially in the areas of biomedicine and photonics devices.There is no universally favored spectral profile in a variety of specific applications.We expect upconversion (UC) nanoparticles with the tunable spectral behavior to meet the demand for actual applications.Although the UC emission wavelengths are strictly limited by the electronic structure of the dopant,the spectral profile could be varied by many factors such as the structure,size,and crystallization. Varying matrix host is the most convenient approach to dynamically tuning UC that is essential for a variety of studies.However,this approach suffers a significant constraint due to insensitive response of most dopant luminescence centers to matrix host.In this paper,a facile EDTA-assisted hydrothermal approach is developed to the shape-selective synthesis of fluoride microcrystals including NaYF₄ rods,LiYF₄ octahedrons,and YF₃ cuboid brick,by only tuning the pH of the mother liquid.The UC spectra of a series of Yb³⁺/Er³⁺-doped fluoride particles with the different shapes and phases are investigated in detail under a near-infrared co-focused laser excitation.The effects of matrix hosts on UC luminescence attributed to the 4f-4f transitions of the Er³⁺ ions in a single particle are amplified through elevating Yb³⁺ concentration.The associated tuning mechanisms are explored by using the power dependent UC luminescence and the temporal evolutions of up/down-conversion emission spectra. Mechanistic investigation reveals that the sensitive response of Er³⁺ UC emission to matrix host stems from maximal use of the various channels populated luminescence levels.It is well known that the population and depopulation of the luminescence levels strongly depend on the excitation power density,the energy level structure of electron,the ratio of the population ions between the two levels,maximum phonon energy and phonon density.The matrix plays the most important role in both the population and depopulation of the luminescence levels mediated by modifying the radiation relaxation probability and non-radiation relaxation probability via varying lattice symmetry and phonon energy.However,the fine modification of the matrix by doping is not always effective to luminescence tuning.In the current study,comparing with LiYF₄ and YF₃ matrixes,it is interestingly found that NaYF₄ matrix can effectively tune the intensity ratio of red to green luminescence from 0.48 to 6.11 by varying Yb³⁺ concentration from 0 to 98% particle.The result indicates that the multiple aspects in the UC process could be influenced by Yb³⁺ doping NaYF₄ matrix structure.We believe that Yb³⁺/Er³⁺ codoped NaYF₄ matrixes with various Yb³⁺ concentrations will result in applications in displays,biological imaging,chemical sensing and anticounterfeiting.