铕铽共掺杂纳米氧化锌的荧光可调性研究

With the assistance of laser hardening technology and the Li-codoping technology, trivalent europium and terbium ions doped ZnO nanocrystals are prepared via the sol-gel route. The key problems on the mismatch between the ionic radii of the rare-earth dopants and the zinc ions can be solved by the following processes: (i) the trivalent europium and terbium ions are mixed thoroughly with the ZnO nuclei in the sol-gel processing; (ii)the trivalent europium and terbium ions are diffused into the ZnO lattices at laser-generated high temperatures to complete the doping process by replacing the zinc ions in the lattices; and (iii) the dopants are trapped in the zinc points when the ZnO lattices are cooled to room temperate at fast cooling rate. The optical properties, the energy diagrams and the energy tranfers of the trivalent europium and terbium ions doped ZnO nanocrystals are investigated, and the rich energy levels of the rare-earth europium and terbium ions can be introduced into the energy band of the ZnO nanocrystals to realize red and green phosphors, respectively, with the features of high effienciency, narrow spectrum and good chromatic quality. Color tunable ZnO nanocrystals from red to green are realized by tuning the molar ratio of the two dopants europium and terbium in ZnO nanocrystals. The results of this project will solve the key problems on the rare-earth doping in the ZnO nanocrystals, and pave the way for color tunable ZnO-based phosphors to gain wide applications in full-color display technologies.

借鉴激光淬火工艺，辅以锂离子掺杂技术，本项目采用溶胶凝胶法使三价稀土铕、铽离子在溶胶凝胶中与氧化锌晶核充分混合，在激光高温加热的条件下使稀土铕、铽离子扩散到氧化锌纳米晶粒里并对锌离子进行替位掺杂，采用激光淬火技术使氧化锌晶格快速收缩以便于将稀土铕和铽离子套牢于锌离子的位置，从而解决三价稀土离子掺杂过程中离子半径不匹配的问题，将稀土铕、铽离子的丰富能级引入到氧化锌纳米晶体中去，制备出谱带窄、色纯度高的氧化锌红色和绿色荧光材料。研究铕、铽掺杂的氧化锌纳米晶体的荧光特性，探索稀土三价铕离子和三价铽离子在氧化锌纳米晶体中的能级图和能量迁移过程。通过控制稀土铕和铽在氧化锌纳米晶体中的掺杂含量使氧化锌的发光颜色在红色与绿色之间随意可调。这项研究将解决氧化锌纳米晶粒在稀土掺杂方面的科学难题，使氧化锌的荧光在整个可见光区具有可调性，为研制氧化锌全色荧光材料提供一种新思路。

稀土离子掺杂氧化锌纳米晶体是一个科学难题。在本项目中，我们研究了铕、铽离子掺杂氧化锌，结果发现铕、铽离子掺杂氧化锌很困难，成功率不高于3%，其主要原因在于铕离子半径(94.7 pm)、铽离子半径（92.3 pm）与氧化锌中锌离子半径（74 pm）严重不匹配。然后，从正反两方面研究了掺锂掺铁氧化锌、掺铕掺镝掺铽铝酸锶(铝酸钡)的光学特性，确认了六角相氧化锌晶体中锌离子半径与稀土离子半径的不匹配是氧化锌难于被稀土掺杂的根本原因。以此为基础，我们将氧化锌与钼酸盐通过高温固相反应制备出具有锌氧六面体和锌氧八面体结构的钼酸锌材料，使锌氧六面体和锌氧八面体中的锌离子半径增大到90 pm左右，从根本上解决了三价稀土离子半径与锌离子半径不匹配的问题。采用上述方案，我们对钼酸锌中的锌氧六面体和锌氧八面体进行铕、铽离子掺杂，分别获得了谱带窄的红色和绿色荧光粉体材料，它们的发光性能稳定，掺杂的成功率接近100%。通过改变铕、铽的摩尔比，实现了铕铽共掺杂的锌氧六面体和锌氧八面体的荧光在红色与绿色之间随意可调。这项研究表明：将氧化锌的锌氧四面体结构改变为锌氧六面体和锌氧八面体的结构，可以从根本上解决三价稀土离子半径与锌离子半径不匹配的问题，从而以近于100%的成功率制备铕、铽掺杂的氧化锌纳米材料，并使其荧光在红光和绿光之间可调。