Preparation, Photoluminescence Properties And Application Of Near-UV LED Pumped Red-emitting Phosphors

In this dissertation, we mainly focus on the red-emitting phosphos under excitation at nearultraviolet, and prepared various red-emitting phosphor with different emitting wavelength,e.g., LiEuMo_2-xSi_xO₈and Li_1-3xTb_xEuMo₂O₈phosphor with strongest emitting wavelength at616nm, Y₂Ti₂O₇:Eu³⁺phosphor with strongest emission wavelength at591nm, Ba₃MgSi₂O₈:Eu²⁺, Tb³⁺, Mn²⁺phosphor with strongest emission620nm, and study in detail the influenceof modification of host crystal lattice, energy transfer design, charge compensation andchoose method of flux on photoluminescence properties of phosphor. Based on the abovework, we prepared high color rendering index （CRI） white lighting emitting diodes （WLEDs）device combination near ultraviolet LED chips （） with green-emitting phosphors（Ba,Sr）2SiO4:Eu²⁺and （Sr,Mg）4Si3O8Cl:Eu²⁺blue-emitting, The main contents as follow:For LiEuMo₂O₈phosphor with scheelite structure, we focus on modiy host crystal latticefor enhancement the red-emitting intensity. Results indicated that Si partly replace the Mo,red-emitting intensity can be improved1.3times at x=0.2. Excitation and absorpbtion spectraindicated that Si-doped result in the charge transfer band from420nm blue shift to360nm，reduce the absorbtion of host in near ultraviolet （360-420nm）, increase the probablility ofexcitation and emission of phosphor. Tb³⁺partly substitude for Li, results indicated thatintroduction of Tb³⁺can significatntly improve the red-emitting intensiy under excitation atnerar ultraviolet, the luminous intensity can be increase1.4times at x=0.04. Excitation andlifetime spectra suggest that energy transfer from Tb³⁺to Eu³⁺can enhance the probability ofexcitation and emission.Novel pyrochlore Y1.55Ti2O7:0.45Eu³⁺orange-red emission phosphor has been synthesizedby high-temperature solid-state reaction. The results suggest that this phosphor showorange-red emitting at591nm （5D0→7F1） under NUV excitation. Luminous intensity ofred-emitting at616nm increases with increasing content of Eu-doped, and reach the maxmum.This orange–red phosphor Y1.55Ti2O7:0.45Eu³⁺shows high thermal quenching temperature（T50%） even up to376°C, and be consider as a promising luminescence thermometry at hightemperature. In addition, we chose H3BO3，NH4Cl，NaCl，NH4F，NaF，LiF as flux tooptimize the condition of Y_2-xTi₂O₇:xEu³⁺phosphor. Experimental results show that NaF isthe best one among the five flux materials, can significantly improve the luminous intensityover16times. According to SEM, EDAX Mapping and CL spectra analysis result indicatedthat NaF flux can modify the paricle morphology and homogenize activator distribution,which is acctributed to the melting point of NaF much more approach to the synthesis temperature of Y_2-xTi₂O₇:xEu³⁺phosphor.According to CL, EDAX Mapping, XRD analysis result of Ba₃MgSi₂O₈:Eu²⁺, Mn²⁺phosphor indicated that green-emitting peak at505nm is ascribed to byproducts Ba₂SiO₄rather than Ba₃MgSi₂O₈:Eu²⁺, Mn²⁺phosphor.Tb-doped can inhibit the formation ofbyproducts Ba₂SiO₄. Photoluminescence and flurescence microscope results suggest thatTb-dped not only reduce green-emitting intensity from byproducts but also can significantlyimprove the red-emitting intensity of phosphor, and luminous intensity reach maxmum at x=0.1. As a charge compensator, Tb³⁺-doped can help the formation of a single phaseBa₃MgSi₂O₈, and improve the efficiency of energy transfer from Eu²⁺-Mn²⁺. Enhanced redemission of Ba₃MgSi₂O₈:Eu²⁺, Tb³⁺，Mn²⁺was discussed in terms of Eu²⁺→Tb³⁺→Mn²⁺energy transfer.