Research On Preparation And Spectrum Tuning Of A₃MgSi₂O₈: Eu²⁺, Mn²⁺ (A=Ca, Sr, Ba) Phsophors For Near-UV LED

In this M. S. thesis, the author discusses the synthesis, micro-structure, spectra of A₃MgSi₂O₈ (A=Ca, Sr, Ba): Eu²⁺, Mn²⁺ phosphors for near-ultraviolet (NUV) light emitting diodes (LEDs). The phosphors are aimed to be applied to white LEDs (WLEDs) with high color rendering index (CRI) and functional solid-state lighting (FSSL) for plant cultivation. In details, the following four aspects of original works have been proposed.1. The origin of 505nm-peaked photoluminescence of so-called single host full color phosphor Ba₃MgSi₂O₈: Eu²⁺, Mn²⁺ is found and proved to be a result of intermediate phase Ba2SiO4: Eu²⁺. And the formation of the intermediate phase is ascribed to the tendency of phase equilibrium during firing process. Addtion of NH4Cl flux plays a role of inhibiting the formation of the intermediate phase and improving the crystallinity of desired Ba₃MgSi₂O₈. Similar conclusions could be applied to Ba₃MgSi₂O₈:Eu²⁺ and analogous for A₃MgSi₂O₈:Eu²⁺, Mn²⁺ (A = Sr, Ca).2. Photoluminescence enhancement effect of Ba₃MgSi₂O₈: Eu²⁺, Mn²⁺ sample synthesized via spray pyrolysis method is observed. Changing the temperature of inlet air during spraying has not an significant effect on diameter distribution of phosphor spheres, but on photoluminescence intensity. The photoluminescence enhancement effect is drawn to enhancement of crystalinity, good NUV absorbtion and light extraction of sample by spray pyrolysis.3. In terms of the new model of crystal structure of Ba₃MgSi₂O₈: Eu²⁺, Mn²⁺ phosphor proposed by T. Aitasalo et. al., utilizing Van Uitert empirical formula the author has calculated the energy of electron transition of Eu²⁺ substituting different Ba²⁺ sites. And the calculated results are in good agreement with the ones obtained by multi-peaks Gaussain fit of experimental data, while the Merwinite crystal structure is proved to be not suitable for Ba₃MgSi₂O₈. Mn²⁺ is also proved to substitute to Ba²⁺ site, and BaII site is preferable.4. BaxSryCazMgSi2O8: Eu²⁺, Mn²⁺ (x+y+z=3) phosphors are proposed to two types of FSSL applications, WLED with high CRI and FSSL for plant cultivation. Resonant energy transfer phenomenons are generally found on BaxSryCazMgSi₂O₈: Eu²⁺, Mn²⁺ (x+y+z=3) phosphors. Taking Ba₃MgSi₂O₈: 0.02Eu²⁺, xMn²⁺ for example, the effect of doped Mn²⁺ concentration on emission spectrum and energy transfer between Eu²⁺ and Mn²⁺ is calculated, and dipole-dipole interaction type is found in resonant energy transfer of Ba₃MgSi₂O₈: 0.02Eu²⁺, xMn²⁺. The feasibility of blending phosphors with Ba3MgSi2O8: 0.02Eu²⁺, 0.2Mn²⁺ and Ba0.8Sr1.2SiO4:0.02Eu²⁺ for WLED with high CRI is also discussed.