The Research And Synthcsis Of Long-wavclcngth Emitting Phosphors For W-LEDs

This work is focused on synthetizing novel phosphors that are more suitable forW-LEDS. Three different kind of phosphors have been synthetized and researched:Tb2.94Al_5-2xMg_xSixO12:Ce³⁺0.06（0≦x≦0.6）（blue light excited）, Sr₃Al_xSi_1-xO5:Ce³⁺, Eu²⁺（purple light excited） and flower-like nano Gd₂O₂S:Eu³⁺（NUV excited）.In the second chapter, Tb_2.94Mg_xAl_5-2xSi_xO₁₂:Ce³⁺_0.06（TMASG:Ce） weresynthesized by high temperature Solid-State Reaction （SSR） at different temperaturefrom1650to1550oC. Samples with x=0.1,0.2,0.3,0.6were fabricated andcharacterized using powder X-ray diffraction （XRD） and room-temperaturephotoluminescence spectroscopy. In this work, the excitation and emission spectraindicate that the phosphor can be excited effectively by the blue light （450-550nm）and exhibit a satisfactory orange-yellow emission from550to575nm. The reasons ofthe red-shift of the phosphor have been discussed. A crystal field analysis of the Ce³⁺5d energy levels is conducted to explain the correlation between the TMASG:Celattice expansion and the Ce³⁺ energy level changes. The CIE chromaticitycoordinates of the phosphors are tuned from （0.465,0.527） to （0.512,0.483）. Thisindicates a prospective for application of this novel phosphor in white light emittingdiodes （LEDs）.In the third chapter, trivalent ions B³⁺, Al³⁺and Ga³⁺have been introduced intothe Sr₃SiO₅:Ce³⁺in this study. Among these ions, Al³⁺and Ga³⁺act as chargecompensators and significantly enhance the emission of Ce³⁺maximum about100%and90%, respectively. Then, Al³⁺, Eu²⁺co-doped Sr₃SiO₅:Ce³⁺phosphors have been researched, which indicate the emission spectra can be tuned from530to575nmwith changing the concentration of Eu²⁺. The CIE chromaticity coordinates of thephosphors were calculated from （0.342,0.518） to （0.442,0.479）. This indicates aprospective for applying in Day-Light LEDs or Warm-White LEDs.While in the fourth chapter, Uniform Gd₂O₂S flower-like nano-assemblies wereprepared through one-pot mild solvothermal synthesis. The parallel nanoplates arethe bulding blocks, in thickness and20-30in diameter. Ethanediamine, main solvent,plays an important role in dissolving a large amount of sulphur and producing activeS^2-ions, which results in the direct formation of Gd₂O₂S. Oleylamine, capping agent,controls the growth of plate like structure. Under UV excitation, Gd₂O₂S:Eu³⁺nano-phosphor shows good red luminescence with main emission peak at627nm.Under980nm laser excitation, Gd₂O₂S:xYb³⁺,1%Er³⁺nano-phosphors exhibittuneable emission, shifting from greenish yellow to orange-yellow, with increasingYb³⁺content.