The Potential Application Of Noncentrosymmetric Rare Earth Borates For Near-UV LED Pumped Red Phosphors

This thesis concentrates on the luminescent property of rare earth polyborates,where the coordination of rare earth cation is quite noncentrosymmetric.We have carried out following work in order to developing new red phosphors:the high temperature solid-state reactions have been used to synthesized rare earth poloyborates.And the properties of luminecences from different activiters,for example,Eu³⁺,Tb³⁺,Tm³⁺and Dy³⁺,have been discussed.Single-phased white light emitting phosphor has been prepared in YGa₃?BO₃?₄ host by controlling the droping concentration of Eu³⁺,Tb³⁺,Tm³⁺or Dy³⁺and Tm³⁺.But beyond that,we discussed the luminesences properties of Cd₄Gd_1-xEu_xO?BO₃?₃?0?x?1?with crystal local structure distortion after Ca²⁺doped.This method offered a new method to adjust the fluorescence properties of various luminescent centers through controlling the coordinations resided by activiters rather than adjusting the concentration of activitersy.The main experimental results showed just like following:1.Cd₄Gd_1-xEu_xO?BO₃?₃?0?x?1?were synthesized by traditional high-temperature solid-state reactions,and the photoluminescences properties have been discussed in detail.Moreover,in most Eu³⁺-based phosphors,the CT absorption is much stronger than the f-f transitions,because the later ones are parity-forbidden.In Cd₄Gd_1-xEu_xO?BO₃?₃,the f-f transitions are quite strong in the near-UV and even blue light regions.So,Cd₄Gd_1-xEu_xO?BO₃?₃?0?x?1?should be certified an excellent near-UV LED pumped red phosphors with low thermal quenching.2.?Cd1-yCay?4Gd0.3Eu0.7O?BO3?3?0?y?1.0?were synthesized by adjusted the lattice local stracture around Eu³⁺live in.We found the photoluminescence of Eu³⁺has been improved after Cd²⁺were subsitituded for Ca²⁺.Rietveld refinements were performed for the randomness of occupation with Eu³⁺.The photoluminescences droped Eu³⁺could be improved whatever ions(Ca²⁺,Zn²⁺,Sr²⁺)was choiced for subsitition,and the larger difference of Cd²⁺and droped ion radius could lead to much changes.In-situ high-temperature photoluminecsece spectrum also have been measured for three representive samples,and the results shown the phololuminescences and the thermal quenching have been improved after droped other metal ions,just like Ca²⁺,Zn²⁺,Sr²⁺.3.Single-phased white light emitting phosphor was prepared in YGa₃?BO₃?₄ host by controlling the droping concentration of Eu³⁺,Tb³⁺,Tm³⁺.We proved the energy transfer beween Tb³⁺and Eu³⁺.Then,contronling the droping concentrations,we got a promising near-UV LED pumped white Phosphor.4.Inspiring work3,we designed a near ultraviolet excited white phosphor(Dy³⁺and Tm³⁺doped YGa3?BO3?4).When co-doping Dy³⁺and Tm³⁺in YGa₃?BO₃?₄,there was no energy transfer between them.Eventually,a white light emission could be obtained with the CIE coordinates of?0.3252,0.3292?in Y0.91Dy0.07Tm0.02Ga3?BO3?4 under 364 nm excitation.