Synthesis And Optical Properties Of Rare Earth-doped Phosphate Phosphors For White Light-emitting Diodes

Phosphate has been extensively studied as a conventional matrix for luminescent materials because of their low sintering temperature, high luminous efficiency and excellent thermal stability. Based on the above considerations, we take Ca3(PO4)2 as matrix to synthesize a series of rare earth or trans ition metal ions-doped alkaline earth phosphate phosphors by conventional solid state reaction, and also investigate their optical properties as well as application in white light-emitting diodes in detail. The main research contents and results are listed as follows :1. A cyan-emitting phosphor ??-Ca3(PO4)2:Eu2+(??-TCP:Eu2+) has been synthesized by conventional solid state reaction. The phosphor shows strong and broad absorption in 250-450 nm, the emission spectrum is dominant at around 480 nm, and the optimal emission intens ity was obtained at x = 1.5%, with the CIE color coordinate(0.217, 0.331). Under excitation at 370 nm, emission intens ity of the optimized ??-TCP:Eu2+ was found to be 82% of that of the commercial BAM, the absolute internal and external quantum efficiency of the optimized ??-TCP:Eu2+ are 60% and 42%, respectively. The thermal quenching results determined the Eu2+ activation energy in ??-TCP is about 0.28 eV. Moreover, a white LED lamp was fabricated by coating a blending of ??-TCP:Eu2+, blue-emitting BAM:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors on a near-ultraviolet(375 nm) LED chip, driven by a 350 mA forward bias current, and produces an intense white light with a color rendering index of 75.2. Eu2+ and Mn2+ co-activated ?-Ca3(PO4)2(?-TCP) phosphors have been synthesized by conventional solid state reaction. The site occupation and photoluminescence of Eu2+ and Mn2+ have been identified and discussed in detail. The energy transfer from Eu2+ to Mn2+ has been demonstrated to be a resonant type via a dipole-quadrupole mechanism, and the critical distance(RC) calculated by quenching concentration method is 21.79 ?. A color-tunable emission from violet-blue to red in ?-TCP:Eu2+, Mn2+ phosphors can be realized via the energy transfer from Eu2+ to Mn2+ ions.3. Eu2+ and Mn2+ co-doped Ca3-mSrm(PO4)2:Eu2+, Mn2+ phosphors have been synthesized by conventional solid state reaction. The continual introducing of Sr2+(0 < m ? 1.5) induced the redistribution of Eu2+ among different Ca sites in Ca3-mSrm(PO4)2:Eu2+, resulting in emission hue variation from violet-blue to yellow. In addition, we obtained a series of full-color-emitting Ca2.7Sr0.3(PO4)2:Eu2+, Mn2+ phosphors over the whole visible range, of cause including the white light emission by energy transfer between Eu2+ and Mn2+. White light-emitting diodes(LEDs) were fabricated through the integration of 375 nm NUV chips and single-composition white-emitting phosphor Ca2.7Sr0.3(PO4)2:0.8%Eu2+, 3.0%Mn2+ into a single package, which shows a warm white light with color coordinates of(0.40, 0.41) and color temperature of 3731 K.