Er3+掺杂卤氧化铋晶体雪崩发射效应及其调控机制的研究

Among the three basic upconvertion （UC ）mechanisms, the photon avalanche (PA) is re-garded as the most efficient one, due to the special feed-back, or "looping", cycle energy transfer (ET) property. However, the generation of avalanche UC is practically much great fewer than the UC phenomena via other two basic mechanisms, as the necessary conditions for constructing this process, and the threshold condition for the efficiency of CR is not easily fulfilled. In preiviou work, We found the controllable photon avalanche (PA) UC of Er3+ ion at violet, green , red and NIR emission bands from Er3+doped Bismuth oxyhalides crystals, which could be realized under excitation of near infrared (NIR) lasers. Especially, it show that besides the power density, the "looping" and the cycle numbers of the PA processes could be controlled through the control of dopant concentration and synthesis methods for nanomaterials. Researches on the efficient UC phenomenon defined as or similar to a PA process, can offer new insights and extensive understandings for the PA mechanism and its necessary conditions, which may lead to a breakthrough for the potential use of PA materials. The project will also address a very important scientific area of clarifying the PA emission mechanism of Er3+ doped Bismuth oxyhalides as well as the consturction condition for PA behavior associated with crytals sturcutre and excitation light. To address this challenge, this project will be exploited in both turning of Bismuth oxyhalides structure to produce an mechanism that decides the novel Er3+ activtated multi-band PA phosphorescence and the analysis of laser properties which is directly associated with the generation of PA emissions. This project ultimately seeks to go beyond the evident limits of rare earth doped materials for producing visible and NIR PA phosphorescence. The study may offer a better understanding of the mechanism of PA emissions and the principles of construting PA behavior. Moreover, owing to considerable strong GSA at NIR band and facile preparation of single crystal, Er3+ doped Bismuth oxyhalides crystals are potentially useful for the development of efficient UC solid-state lasers.

光子雪崩是稀土离子上转换中一种高效的形成机制，但传统雪崩发射行为构建规律不明、实际效率低下，阻碍了其研究进展与应用。研究中我们发现铒激活卤氧化铋具有独特的雪崩发射行为，近红光外光激发下410-1550nm多个波段呈现高效的同步雪崩发射现象，且雪崩循环特征可通过外掺离子、合成方法及激发光性质等多重因素进行调控。这类材料全新的雪崩发射及可调控化行为与以往完全不同，其机制探索有望为光子雪崩研究带来新的突破。因此本项目提出从卤氧化铋结构与铒离子发光性质的实验调控出发，与激发光波长、频率、功率密度等光激励诱导因素相关联，结合J-O理论和第一性原理的理论计算分析，研究铒激活卤氧化铋光子雪崩发射形成的材料结构与光激励诱导条件，阐明其构建及调控机理。项目实施将有助于雪崩上转换理论体系的发展，为设计制造高效光子雪崩材料提供理论基础和技术支持，并推动其在激光器、光学开关等领域的应用，具有很好的理论和现实意义。

光子雪崩是一种传统稀土掺杂发光材料中难以实现的光学现象，对激光泵浦功率要求极高。另外，如何实现稀土离子的光子雪崩可设计化，目前依然缺乏有效的理论依据。我们首先在层状的氯氧化铋体系中发现了Er离子的全波段光子雪崩发光。这类现象这可在室温条件下利用普通的连续激光轻易获得，有望实现这类独特发光现象应用的突破。本项目以Er掺杂卤氧化铋为基础，从1）卤氧化铋的材料结构原理；2）稀土离子的雪崩发射机制；3）激光与稀土离子及卤氧化铋的相互作用，三个方面开展了近红外激发下Er离子光子雪崩机理的探索与构建机制。. 研究发现：1）卤氧化铋层状结构形成的取向自发极化及内电场是形成稀土离子光子雪崩现象的重要原因之一。内电场可以利用局域场效应实现稀土离子激发增强，布局能级过饱和效应，以及通过促进光生电子和空穴分离抑制非辐射弛豫等作用机制，促进光子雪崩的形成；在Bi系层状极化材料中具有普适性；.2）卤氧化铋层状结构独特的层间范德华力连接，导致表面极易形成缺陷；在近红外激光很低的功率辐照下，缺陷能级利用多光子效应实现带隙跃迁，在层状半导体中构建全新的光子雪崩机制；. 3）稀土离子在层状半导体中的雪崩循环机制发生了根本性的改变。在内电场作用下，光诱导缺陷能级在激光作用下利用多光子效应，形成近红外铁电光伏效应和带隙跃迁，并利用下转换布局过程实现了可见波段的光子雪崩；而近红外波段的光子雪崩发射则是铁电光伏效应形成后，稀土离子可见波段与近红外波段交叉作用增强的结果。. 上述研究表明，当基质的晶体结构从传统的三维转变为二维晶体后，稀土离子与基质之间的相互作用关系发生了全新的改变，稀土离子的跃迁行为也随之变化，从而能够实现很多传统稀土发光材料难以观察和实现的发光行为。Er掺杂卤氧化铋光子雪崩行为的研究，不仅为光子雪崩行为的构建机制打开了全新的道路，同时也帮助我们打开了认识稀土离子发光材料新的维度。