Investigation On Nitriding Efficiency And Spectral Characteristics Of Ba₉Y₂Si₆O₂₄ Based Phosphors For White LEDs

LED-based solid state lighting devices have gradually replaced traditional light sources.As a new generation of lighting sources,white LEDs are outstanding in terms of robustness,luminous efficiency,environmental friendliness,and energy saving.In addition,phosphors play a very important part in determining the performance of white-LEDs.At present,the commercial white-LEDs is based on blue LED chips combined with YAG:Ce³⁺yellow phosphors.However,this white-LEDs have the defects of low color rendering index?Ra<80?and high color temperature?CCT>6000K?,and they are unfavorable to human eyes for long-term usage.Therefore,many researchers began to improve the luminescence of YAG phosphors by nitriding or cationic substitution.In addition,more and more researchers have begun to pay attention to the potential applications of silicate phosphors because of their well stability,abundant raw materials,and low cost.Ba₉Y₂Si₆O₂₄-based phosphors as a novel silicate phosphor exhibit good luminous efficiency and can be effectively excited in the blue or ultraviolet range.However,compared with YAG phosphors and some nitride phosphors,their luminescence intensity and thermal stability are still somewhat inadequate.This paper is aimed at adjusting the fluorescence spectrum of Ba₉Y₂Si₆O₂₄-based phosphors by nitriding and ions co-doping to developed novel and stable phosphors.Main researches are shown as follows:?1?Ba₉Y₂Si₆O_24-1.5xN_x:0.06Ce³⁺phosphors were prepared by high-temperature solid-state reaction in N₂/H₂ environment.The Occupancy and luminescence properties of Ce³⁺ ions were analyzed by XRD analysis,Rietveld refinement,fluorescence spectra analysis and first-principles calculations.Compared with the Ba₉Y₂Si₆O₂₄:Ce³⁺phosphor,the luminescence intensity has been greatly improved for the nitrided phosphor.p-d orbital hybridization between N^3--p and Ce³⁺-d orbital after the nitridation leads to red shifts of Ce³⁺_?Ba?lattice ionic emission peaks.Meanwhile,the energy transfer was pointed from Ce³⁺_?Ba?lattice sites to Ce³⁺_?Y?lattice sites by the spectral analysis.By optimizing the N^3-concentration,there exists abnormal outstanding thermal-stability.At 180?,the luminescence intensity is 129%of room temperature.The whole photoluminescent properties of nitrided Ba₉Y₂Si₆O₂₄:Ce³⁺phosphors were superior to that of Ba₉Y₂Si₆O₂₄:Ce³⁺phosphors.It indicates that the phosphor has good potential for White-LED. ?2?Based on Ba₉Y₂Si₆O_23.85N_0.1:0.06Ce³⁺,Mn²⁺was introduced into the phosphor by co-doping technique.The energy transfer and spectral regulation between Ce³⁺?Mn²⁺ was studied.According to the spectral analysis of Ce³⁺single-doped and Mn²⁺ single-doped,the effective energy transfer of Ce³⁺_?Ba??Mn²⁺and Ce³⁺_?Y??Mn²⁺is present in the Ba₉Y₂Si₆O_23.85N_0.1:Ce³⁺,yMn²⁺phosphors.Under395 nm exciting,the emission is mainly the blue-green bond of Ce³⁺_?Y?center,and the energy transferof Ce³⁺_?Y??Mn²⁺ is simply analyzed.Correspondingly,under 330 nm exciting,the emission of the phosphor can be shifted from the blue-green bond to the red bond with the change of the Mn²⁺concentration.The energy transfer efficiency of Ce³⁺_?Ba??Mn²⁺can reach 68%,and the mechanisms of energy transfer is determined to be an quadrupole-equadrupole interaction by the fluorescence lifetime curves.?3?Ba₉Y₂Si₆O_24-1.5xN_x:0.6Eu²⁺phosphors were prepared by high-temperature solid-state reaction.The synergistic effect of the nitriding technique was studied.At the optimum N^3-concentration,Mn²⁺was introduced into in host,and energy transfer mechanism of Eu²⁺?Mn²⁺was analyzed.Compared with the Ba₉Y₂Si₆O₂₄:0.6Eu²⁺phosphor,the luminescence intensity of Ba₉Y₂Si₆O_24-1.5xN_x:0.6Eu²⁺increases about1.8 times at the optimal N^3-concentration.And the thermal stability of the nitrided Ba₉Y₂Si₆O₂₄:0.6Eu²⁺phosphor has also been improved.By doping with Mn²⁺ions,the effects of Mn²⁺on the spectrum and fluorescence lifetime of Eu²⁺ ions were analyzed and the energy transfer mechanism between Eu²⁺?Mn²⁺controlled the spectral regulation from green bond to red bond.The thermal stability curve shows that the addition of Mn²⁺ reduces the thermal stability of the phosphor,but its external quantum efficiency is improved.According to the CIE diagram,the best white light can be obtained by properly controlled the proportion of Eu²⁺and Mn²⁺.