离子掺杂诱导稀土、铋硼酸盐高压相的常压合成及光学性质优化

Rare earth and bismuth-containing borates have always been popular owing to their outstanding performance as photoluminescence and nonlinear optical materials. Recently, people applied the high temperature-high pressure method to prepare novel metal borates with complex compositions or crystal structures, however, their optical properties were rarely investigated because the resultant sample is usually in a small quantity and the even worse problem is that it always contains a high level of structural defects, which will significantly reduce the optical responses. In fact, the difficulty in ambient-pressure preparation of the high-pressure (meta-stable) form of metal borates is due to either the over-high reaction potential barrier or the over-low thermal stable temperature. According to the preliminary study, the applicant noticed that the Bi3+-to-rare earth cations substitution could greatly reduce the reaction potential barrier, on the contrary, the rare earth cations-to-Bi3+ doping could raise the thermal temperature upper limit. Therefore, the major novelty of this project is to utilize the mutual substitution of Bi3+ and rare earth cations to stabilize the high-pressure polymorph of metal borates at ambient pressure, those originally should be prepared with the assistance of high-pressure method. The systematic investigation on their optical performances is thereafter allowed. In addition, the applicant noticed that some rare earth or bismuth-containing borates with nonlinear optical responses are outstanding photoluminescent hosts, because the so-incorporated activators (like Eu3+) may occupy irregular coordination sites, and it is obviously beneficial to boost its f-f transitions, which are located in the near-UV or visible light range. Such materials are good candidates for near-UV and visible light LED excited phosphors.

稀土和铋硼酸盐由于在荧光和非线性光学材料领域表现卓越而备受关注。近年来，人们利用高温高压法制备了一系列具有复杂晶体结构的新型金属硼酸盐，但是对其光学性质的研究却几乎空白。这可能是由于高压制备的样品量少且常含有结构缺陷，不利于光学性质研究。事实上，金属硼酸盐高压相难以在常压下制备的主要原因是其反应势垒过高(不反应）或热稳定温度过低（易分解或熔化）。申请人通过前期研究发现，利用铋对稀土离子掺杂可降低成相反应势垒，稀土对铋离子掺杂则可提高目标硼酸盐的热稳定温度上限。因此本项目的核心创新点即利用稀土和铋离子的相互掺杂使得原本必须利用高压手段合成的硼酸盐在常压下也可以制备，随后则对其开展系统的光学性质研究。此外，申请人发现一部分具有非线性光学性质的稀土或铋硼酸盐也是非常好的荧光基质，因为引入的激活剂离子（如Eu3+）占据不对称配位环境，其f-f跃迁吸收强，适合作为近紫外-可见LED激发荧光粉。

我们利用稀土离子和铋离子在结构化学上的相似性进行离子掺杂，调节目标化合物的热力学稳定区间，使得原本的亚稳相（例如合成温度过高而超过熔点，或者过低而不能跨过反应势垒）可以在常压条件下直接烧结成相。据此，我们成功合成了稀土离子掺杂的高压相δ-BiB3O6和铋离子掺杂的高压相β-REB3O6。此外，我们利用Bi离子的荧光敏化作用，在若干硼酸盐基质中（如K7CaY2(B5O10)3和YCa3(GaO)3(BO3)4）进行Bi3+/Eu3+和Bi3+/Tb3+双掺，获得了一批内量子效率且高颜色可调的荧光粉。我们发现了具有新结构的γ-REB5O9，利用粉末X射线衍射方法解析了晶体结构，研究了其与α-和β-晶型之间的结构关系，尤其研究了改变离子半径大小、合成温度、合成压力后的成相或相变关系。我们知道Eu3+处于非中心对称的配位环境时，其位于近紫外区的f-f跃迁吸收可以大幅增强，因此我们以YGa3(BO3)4、Cd4GdO(BO3)3、LaB4O6(OH)2Cl、CaBi2B2O7、LiCaRE5(BO3)6五种非线性光学材料以及金属离子局部结构为非中心对称环境的ZnLaB5O10和LiSrY2(BO3)3作为荧光基质，开展了包括稳态光谱、瞬态荧光、高温荧光、电致发光等表征手段，获得了一批可用于近紫外LED芯片激发的红色荧光粉。总之，本项目研究是利用固体化学方法，包括优化合成条件、掺杂离子和关注结构-性质关系，研究稀土硼酸盐荧光材料，发表了一系列学术论文，达到了预期的研究目标。