Upconversion Luminescence Materials Of Er³⁺ Doped BaTiO₃-based Perovskite Structure

Rare earth luminescent materials have been widely applied to solidlaser, three-dimensional display, optical communication, solar cell,biological fluorescence label field due to high color purity, high energyconversion efficiency, long fluorescent life and high stability againstirradiation. The structure and luminescence properties have beensystematically studied by Sol-gel method and high temperature solidphase method in this thesis. The results imply that it could be applied tothe structure probe field. The main contents are as follows.Er: BTO films had been fabricated by Sol-gel method and thepreparation process was investgated. Meanwhile, we prepared the filmsof Er substituted different site by controlling Ba/Ti ratio andinvestigated the structure, morphology and luminescence properties. It isfound that the crystallization of the films has a great effect onluminescent properties, but its fluorescence branching ratio reallyreflects the information of Er occupy different site case.In order to better reflect the influence of Er occupied sites onluminescence properties, we synthesized Er: BTO powders by hightemperature solid phase method and investigated the effect of Ersubstituted site and concentration on the upconversion luminescenceproperties. The variation of luminescent properties is found to be relatedto the chang of crystal field symmetry induced by Er occupying differentsites. In addition, according to the principle of charge compensation, wedoped Li+in the A-site of BTO-A powders and Nb⁵⁺in the B-site ofBTO-B powders. The structure and luminescence properties wereinvestigated and it was found that their luminescence intensity wassignificantly improved. It is well known that phase structure change of host will inevitablyvary luminescent properties. Therefore, the composition of Ba/Sr inBa_xSr_1-xTiO₃phosphors doped with Er3+has been varied to investigatethe effect of phase structure on the upconversion photoluminescenceproperties. With the structure transition from the cubic to the tetragonalphase, the obvious splitting of PL spetra accompanied with enhancementof PL intensity is observed. It could be attributed to the decrease of thelocal crystal field symmetry surrounding Er3+arised by the variation ofphase structure. Additionally, the upconversion mechanisms are alsodiscussed in detail through laser power dependence. The microscopicmechanism of PL intensity change is discussed.