稀土离子掺杂弛豫铁电晶体的生长与上转换发光研究

PMN-based relaxor ferroelectric crystals have significant piezoelectric, dielectric and electrostrictive properties. Recent research, moreover, has indicated that rare earth ion doping can not only improve the piezoelectric properties of the PMN-based relaxor ferroelectric crystals but also induce their up-conversion luminescent properties. This project chooses PMN-based relaxor ferroelectric crystals such as PMN-PT and PMN-PSN-PT as the host crystals and rare earth ions such as Ho3+, Tm3+, Er3+, Yb3+, et cetera as the luminescent active ions, either singly doping or codoping, to prepare crystals with high piezoelectric properties and up-conversion luminescent properties. Then, based on the converse piezoelectric effect and the electric domain feature, at static and resonant states, the electric field modulated up-conversion luminescence is going to be realized by controlling the crystal field, i.e. a high-performance material will be provided for electric field modulated luminescent devices using electric fields to alter the luminescent intensity and wavelength. This research aims to deal with the fundamental technical problems restraining the growth of large-size relaxor ferroelectric crystals doped with rare earth ions, so as to prepare large-size up-conversion luminescent relaxor ferroelectric crystals and obtain the crystal growth technology. Next, the luminescence rule of relaxor ferroelectric crystals doped with rare earth ions, the effect and mechanism of electro-optical coupling, and the effectiveness and rule of electric field modulation will be explored. Also, the mechanism of rare earth ions improving the electrical properties of the relaxor ferroelectric crystals will be revealed. These results will provide theoretical and technical supports for the research, development and application of materials utilized for electric field modulated luminescent devices.

PMN基弛豫铁电晶体具有优异的压电、介电和电致应变性能，而最近的研究发现稀土离子掺杂不仅能够改善此类晶体的压电性能，而且能够使其具有上转换发光特性。本项目选择PMN-PT、PMN-PSN-PT等弛豫铁电晶体作为基质晶体，采用Ho3+、Tm3+、Er3+、Yb3+等稀土离子单独或共掺杂使其同时具有高的压电性能和上转换发光性能，再利用其逆压电效应和电畴特征，在静态和谐振态，通过电场调制稀土离子周围的晶格场，实现电场调制上转换发光，即通过电场改变光强和波长，为电场调制发光器件提供一种高性能材料。本项目拟研究制约大尺寸稀土离子掺杂弛豫铁电晶体生长的技术基础问题，研制出大尺寸上转换发光弛豫铁电晶体，获得晶体生长技术；探明稀土离子掺杂弛豫铁电晶体的发光规律、电光耦合效应与机制、电场调制有效性与规律，亦搞清稀土离子改善其电学性能的机制，为电场调制发光器件用材料的研究、开发与应用提供理论依据和技术支撑。

基于现代科学技术对多功能材料的日益需求，本项目采用稀土离子对传统的弛豫铁电晶体进行改性，力求开发出集压电、铁电和发光特性于一身的新型弛豫铁电晶体材料。基于此，首先采用高温溶液法生长并研究了不同掺杂体系（Eu3+掺杂PZN-PT、Tm3+/Yb3+掺杂PZN-PT、PMN-PEN-PT (E代表Er3+)、PZN-PEN-PT）晶体。研究发现：稀土以离子（Eu3+、Tm3+/Yb3+）和钙钛矿组元（PEN）形式引入均能明显改善PMN-PT和PZN-PT晶体的铁电性能，同时诱导晶体实现特定波长的上、下转换发光，证实了稀土改性在开发发光铁电晶体方面的有效性。其次，采用Bridgman法成功生长了直径为25 mm的Er3+、Ho3+、Sm3+掺杂PMN-PT单晶，获得了大尺寸发光铁电单晶生长技术。对Er3+掺杂PMN-PT单晶的研究结果表明：单晶沿轴向呈现出三方(R)→单斜(M)→四方(T)的相分布。位于R和M相界（以M为主）处的晶体表现出优异的压电性能，其d33>2000 pC/N；位于R和M相界（以R为主）处的晶体，其d33可以通过高温极化显著提升。此外，Er3+掺杂PMN-PT单晶在980 nm激光照射下实现了强的近红外到绿光和红光的上转换发光以及1.45～1.63 um波段的下转换发光，同时在宽温度范围（298～488 K）内表现出明显高于多种上转换发光材料的测温灵敏度。最后，对不同掺杂体系晶体的光谱进行了理论分析，发现其均具有较高的光谱品质因子。作为辅助研究内容，研究了Yb3+/Er3+掺杂SrWO4上转换荧光粉以及PSN-PMN-PT等铁电陶瓷。本项目的研究结果为开发具有发光特性的新型弛豫铁电晶体提供了直接指导，有利于实现晶体的多功能化发展以及拓展晶体的应用领域。