Photoluminescence Properties And Energy Transfer Of Several Oxide/Oxynitride Phosphors For NUV White LEDs

White light-emitting diode?LEDs?,especially for phosphor converted LED?pc-LED?,as an environmentally friendly lighting system,has attracted much attention due to its long operation lifetime,low energy consumption.Phosphor as an important part of pc-LEDs influenced the properties of LED devices.Generally,two different configurations are possible for pc-white LEDs,based on either a blue LED or a near-ultraviolet?NUV??350-420 nm?LED.To solve the existed problems of phosphors for NUV LEDs,we designed and synthesized several new phosphors,and systematically investigated the structure,photoluminescence properties and the energy transfer mechanism between the doped ions.The main works are concluded as follows.?1?A blue-green phosphor Ca15Si20O10N30:Ce³⁺ for NUV white LEDs was synthesized by the solid state reaction method.The maximum emission wavelength of the phosphor can be tuned from about 470 to 520 nm as the content of Ce³⁺ increases due to the energy transfer between various Ce³⁺ activators located in different coordination environments,and this was verified by the time-resolved emission spectroscopy and the variation in the decay rate with respect to the detection wavelength.?2?A yellow-emitting high-Ba3P4O13:Eu²⁺ phosphor was synthesized by the solid state reaction,and the phosphor shows an extreme broad band at around 587 nm with a full width at half maximum of about 175 nm,which is attributed to the 5d-4f transition of Eu²⁺ under NUV excitation.This phosphor shows good absorption in the NUV range and nearly no absorption in the blue region.The change in the time-resolved emission spectroscopy indicates the energy transfer between the Eu²⁺ ions occupying different Ba²⁺ sites.Moreover,a white light with chromaticity coordinates of?0.364,0.357?and color temperature of 4354 K was obtained by blending the yellow-emitting high-Ba3P4O13:Eu²⁺ and the commercial blue-emitting BaMgAl10O17:Eu²⁺ phosphor.?3?A series of Ce³⁺,Eu²⁺ codoped Ca₃Si₂O₄N₂ phosphors have been synthesized by the solid state reaction method.Tunable blue to green emitting colors can be obtained by varying the relative ratios of Ce³⁺ to Eu²⁺ in Ca₃Si₂O₄N₂.Compared with the Eu²⁺ ion singly doped phosphor,the codoped phosphors have wider absorption in the NUV range and stronger emission of Eu²⁺,which are attributed to the effective energy transfer from Ce³⁺ to Eu²⁺.And the energy transfer mechanism is demonstrated to be a dipole-dipole interaction.?4?A series of single-component Ce³⁺,Mn²⁺ ions codoped color-tunable CaSr₂Al₂O₆ phosphors were synthesized by the solid state reaction method.The Ce³⁺ activated phosphors have strong absorption in the range of 250-420 nm and can give a blue emission centered at about 460 nm.When Mn²⁺ ions are codoped,the emission of CaSr₂Al₂O₆:Ce³⁺,Li⁺,Mn²⁺ phosphors can be tuned from blue to red through adjusting the doping content of the Mn²⁺ ions,under the irradiation of 358 nm.When the concentration of Mn²⁺ in increased to 0.02,a warm-white light can be obtained with good CIE coordinates of?0.388,0.323?and a low CCT of 3284 K.The energy transfer mechanism from the Ce³⁺ to Mn²⁺ ions is demonstrated to be quadrupole-quadrupole interaction based on the analysis of the decay curves of the phosphors.Moreover,the photoluminescence properties of Eu³⁺ doped CaSr₂Al₂O₆ were also investigated.The difference between the emission spectra of CaSr1.90Al2O6:0.10 Eu and Ca0.90Sr₂Al₂O₆:0.10 Eu revealed that the Eu³⁺ ions occupied nonequivalent Sr²⁺ or Ca²⁺ sites with different site symmetry.