(Ba, Ca) TiO ₃ : Pr ^{3 +} Stress Luminescence Performance Optimization And Ca ₂ Nb ₂ O Study On The Photoluminescence Properties Of ₇ : Pr ^{3 +}

Object can emit light under various forms of stimulation, the stimulation include force, light, electricity, high-energy radiation and so on. Mechanoluminescence（ML） is the emission of phosphors caused by the application of mechanical energy to the solid, the mechanical stimuli include grinding, cutting, collision, striking, friction, etc. Mechanoluminescence can be divided into fracto-ML（FML）, plastico-ML（PML） and elastico-ML（EML）. The light-emitting of the object irradiated by light energy is called photoluminescence（PL）. The process of PL mainly include energy absorption, energy transfer and light emission. The ultraviolet radiation, visible light and infrared radiation can induce PL.First of all, Elastico-mechanoluminescence（EML） in diphase（Ba,Ca）TiO₃:Pr³⁺ with 60 mol% Ca content was greatly enhanced by Gd³⁺ codoping. The optimal EML intensity of（Ba,Ca）TiO₃:Pr³⁺,Gd³⁺ is higher by 235% than that of（Ba,Ca）TiO₃:Pr³⁺. The decreases of both photoluminescent intensity and reflectivity induced by Gd³⁺ codoping suggest the introduction of new trap centers. The thermoluminescent（Th L） measurement has been performed to investigate the effect of codoping on the trap depth and concentration. The consistent dependency correlations of EML intensity and ThL integral intensity on the Gd³⁺ concentration illuminate that the improved EML originates from the increased concentration of traps with suitable depth. A possible EML mechanism for（Ba,Ca）TiO₃:Pr³⁺,Gd³⁺ is proposed on the basis of these experimental observations.Then the Pr³⁺ activated Ca2Nb2O7 phosphors(Ca2Nb2O7:Pr³⁺) was prepared in air atmosphere by solid-state method and sol-gel method, respectively. An interesting phenomenon that the emitted color spectrum originates from Ca2Nb2O7:Pr³⁺ phosphor varies with synthetic method has been observed under UV excitation. The Ca2Nb2O7:Pr³⁺ phosphors synthesized by solid-state method exhibit a strong red emission at 615 nm. The Ca2Nb2O7:Pr³⁺ phosphors synthesized by sol-gel method exhibit an abroad and strong blue emission at 457 nm. There is the feature that distinguishes from other phosphors which synthesized by different method just can emit same color. The properties of Ca2Nb2O7:Pr³⁺ are studied in detail, including XRD, SEM, diffuse reflectance, excitation and emission spectra and CIE color coordinates. Results can be obtained that the main orange-red emission band at 615 nm and blue emission band at 457 nm originate from the Pr³⁺ ions and host lattice of Ca2Nb2O7:Pr³⁺, respectively. The varied luminescence color can be achieved by properly altered the mass ratio of Ca2Nb2O7:Pr³⁺ phosphors synthesized by solid-state method and sol-gel method. The white luminescence with CIE color coordinates of（0.322, 0.305） have been obtained when the mass ratio was 1:1. Our investigation of Ca2Nb2O7:Pr³⁺ phosphors may provide new ideas to design and fabricate novel luminescent materials for UV-LEDs.