Study On Luminescence Properties Of Eu²⁺ Regulated By Anion/Cation Group Substitution And Its Application

In recent years,phosphor-converted white light-emitting diodes（pc-WLEDs）have been used extensively in both solid-state lighting and liquid crystal display backlighting.There are certain problems for both commercial solid state lighting and backlighting at present.In LED lighting,the goal is to achieve full-spectrum sunlight-like lighting,hence the interest in single-substrate white phosphors and broadband yellow phosphors rich in cyan and red light.In the field of liquid crystal display（LCD）backlighting,there is an urgent need to develop new narrow band green phosphors with appropriate peak position and FWHM to replace the currently commercially availableb-Si Al ON:Eu²⁺phosphors in order to achieve a wider color gamut.This research is dedicated to the study of high performance rare earth phosphors with different luminescence characteristics based on different LED applications using rare earth ion Eu²⁺as activator,which are divided into the following aspects.（1）Taking the UCr₄C₄-type RbNa₃（Li₃SiO₄）₄:Eu²⁺blue phosphor as starting model,we successfully synthesize a series of Rb_1+xNa_2.97-x（Li₃SiO₄）₄:Eu²⁺（0.1￡x￡2.5）phosphors by replacing Na⁺with Rb⁺,tuning the color from blue to narrow-band green emission.We demonstrate that Rb⁺-substitution drives phase transition from tetragonal phase Rb₃Na（Li₃SiO₄）₄:3%Eu²⁺to monoclinic phase Rb_1+xNa_2.97-x（Li₃SiO₄）₄,making Eu²⁺ions enter two new,cuboid-like Rb and Na sites and resultant green emission.With optimized content of Rb⁺,Rb₃Na（Li₃SiO₄）₄:3%Eu²⁺green phosphor not only shows appropriate peak position（～526nm）and FWHM（～43 nm）compared toβ-Si Al ON:Eu²⁺phosphor,but also high IQE of 90.2%and superior thermal stability（integrated emission intensity at 150°C is 105.7%of room-temperature performance）.By using the resulting green-emitting Rb₃Na（Li₃SiO₄）₄:3%Eu²⁺phosphor,commercial red-emitting KSF:Mn⁴⁺and blue In Ga N chip,as-prepared WLED show wide-color-gamut of 111.2%NTSC,surpassing recently reported most performance of WLED devices.We believe that UCr₄C₄-type Rb₃Na（Li₃SiO₄）₄:3%Eu²⁺narrow-band green-emitting phosphor hold great potential for wide-gamut full-color LCD devices and merit further study to realize their full potential.（2）Sr₃La（PO₄）₃,which has a（PO₄）^3-anionic group,was chosen as the matrix material,using a strategy of anionic group co-replacement,where the（BO₃）^3-group is used to replace the（PO₄）^3-group in the matrix structure.We have successfully synthesised a series of Sr₃La（PO₄）_3-x（BO₃）_x:Eu²⁺（0￡x￡0.5）phosphors whose luminescent color change can be divided into two stages,the first from blue to white and the second from white to yellow.When（BO₃）^3-has not replaced（PO₄）^3-the spectrum emitted by the sample is a single blue emission peak,as（BO₃）^3-replaces（PO₄）^3-a new emission peak is induced at long wavelengths,when the concentration of（BO₃）^3-is 0.1 the intensity of the two emission peaks are comparable and we achieve white light from a single substrate.As the concentration of（BO₃）^3-continues to increase,the intensity of the blue emission peak gradually decreases and the intensity of the yellow emission peak continuously increases.Using our Sr₃La（PO₄）_3-x（BO₃）_x:Eu²⁺（x=0.1）white phosphor to make WLED devices,we obtained white LED devices with a color rendering index of 90 and a color temperature of 7001.69 K.Using our Sr₃La（PO₄）_3-x（BO₃）_x:Eu²⁺（x=0.4）yellow phosphor and commercial blue phosphor Ba Mg Al₁₀O₁₇:Eu²⁺(BAM:Eu²⁺).The mixture of Sr₃La（PO₄）_3-x（BO₃）_x:Eu²⁺（x=0.4）yellow phosphor and the commercial blue phosphor BAM:Eu²⁺were coated on 365 nm near-UV LED chips to produce WLED devices,its color rendering index is 82.7 and color temperature is 4454.8 K.In this work,a series of boron phosphate phosphors with adjustable luminous color were obtained by using phosphate as matrix and anion Group Co substitution strategy.