Design And Synthesis Oxide-Based Phosphors For White Light-Emitting Diodes Application

Phosphors converted white light emitting-diodes (pc-WLEDs) has been considered to be the next generation solid state lighting (SSL) source due to their advantages of high efficiency, long lifetime, low power consumption and environment-friendly characteristics. As the core component in pc-WLEDs, Phosphors have been extensively studied in resent years. However, current phosphor system lacks of phosphors that with good photoluminescence performance. Therefore, to explore high effciency oxide-based phosphors with high quality is of great significance. To achieve this, the selection principle for phosphors should be summarized, and novel design methods are urgenly requred in the process of phosphors exploring and preparation.In order to synthesis high photoluminescence performance phosphors, we investgated the relationship between the crystal and their luminescence properities, and also explore novel design methods for phosphor preparation. In this paper, we have conducted our research from four aspects:1. Complex perovskite-type MLnMgM’O6:Eu3+(M=Ca, Sr, Ba; Ln=La, Gd, Y; M’=Nb, Ta, Sb) red emitting phosphor with structure representation for NUV/blue light excitation has been synthesized by solid state method. The relationship between their structural and optical properties was investigated by X-ray diffraction (XRD) and photoluminescence (PL) sprctra. The principle for phosphors selection among complex perovskite structured materials has been summed. The quantum efficiency of composition-optimized Ca(La0.6Eu0.4)MgNbO6reached as high as18.1%. The result indicated that Ca(Lao.6Euo4)MgNb06red phosphors may have a potential application for white LEDs.2. Perovskite-type NaLaMgWO6:RE3+(RE=Eu, Sm, Tb) tungstate red emitting phosphor for NUV/blue light excitation has been synthesized by solid state reaction using the "introduce the tungstute into a low t perovskite-type host material" design method. XRD, Scanning Electron Microscopy (SEM), the morphology Energy-dispersive X-ray spectroscopy (EDS), UV-vis absorption spectra and PL spectra were used to characterize the obtained samples. Under464nm blue light excitation, the composition-optimized Na(La0.6Eu0.4)MgW06exhibits high quantum efficiency of332%of Y2O3:Eu3+and104%of another commercial red-emitting compound Sr2Si5N8:Eu2+, and also50.2%of the commercial yellow phosphor Y3Al5O12:Ce3+. The results demonstrated NaLaMgWO6:RE3+phosphors as potential candidates for white light emitting diode pumped by UV or blue chip and also confirmed the guiding significance of the summarized principle in the last chapter. The concept of combined the tungstate with low t perovskite materials also gives a new inspiration for the exploration and selection of the host materials in the field of WLEDs applications.3. Single-composition phosphors Ca9MgM(PO4)7:Eu2+,Mn2+(M=Li, Na, K) and Ca9Al(PO4)7:Ce3+,Mn2+with energy transfer were synthesized by solid state reactions. The result indicates that Ca9MgM(PO4)7:Eu2+,Mn2+(M=Li, Na, K) is a emission-tunable phosphors that can be potentially useful for UV based white light-emitting diodes. Ca9Al(PO4)7:Ce3+,Mn2+is potentially useful as a UV excited red-emitting phosphor in the field of solid state light source. Furthermore, the energy transfer probability between Eu2+/Mn2+or Ce3+/Mn2+in their phosphate host was discussed in detail.4."Co-host" design concept was first proposed for phosphors preparation. Ce3+, Eu2+and Eu3+singly activated and Ce3+/Eu2+/Eu3+-coactivated Ca11(SiO4)4(BO3)2(CSB) phosphors were synthesized by novel and efficient aluminum reduction solid state reactions. XRD, PLE/PL spectra, X-ray photoelectron spectroscopy (XPS) were used to characterize the samples. Under ultraviolet light excitation, the Ce3+, Eu2+and Eu3+singly activated CSB:Ce3+,Eu2+,Eu3+phosphor exhibit intense red, green and blue emissions, respectively. The unique host CSB shows its superior advantages in color balance compared with the widely-used Ca2SiO4, Ca3B2O6and Y3AI5O12. Red, green and blue colors can be controlled by the reduction temperature, and a white light emitting phosphor was obtained by reducing the as-prepared CSB:0.02Ce,0.005Eu powder at700℃for8h. The unique property of CSB in color balance was proposed to attribute to the "group synergies effect". Furthermore, the energy transfer probability was discussed in detail, and the critical distance was calculated. At last, LED lamps have been successfully fabricated using the365nm UV chip combined with CSB:0.02Eu3+, CSB:0.02Ce3+, CSB:0.005Eu2+and white emitting phosphor CSB:0.02Ce,0.005Eu by Al reduced at700℃. They show bright red, blue, green and white light emitting driven by a20mA current.