Preparation And Luminescent Properties Of The Polychromatic Phosphate Phosphor For NUV-LED

With the aggravation of global energy shortage,the development of energy-saving,low emission,environment-friendly and efficient energy materials is an important direction in the current energy field.Fluorescent conversion WLED has the advantages of energy saving,environmental protection,short response time,long service life,small volume and heat generation.So it has become people’s daily lighting tools.At present,with the gradual maturity of the preparation technology of near ultraviolet LED chips,it is an important way to pursue high-quality white light in the future.However,the existing NUV LED with red phosphors have the disadvantages of low luminescence efficiency and poor thermal stability.In addition,compared with the full spectrum of"sunlight",the spectrum of WLED also has a spectral"gap"in the green area（470-510 nm）,which reduces the spectral continuity of WLED devices and makes it difficult to achieve ultra-high color rendering index（Ra>95）,which greatly limits the development and application of WLED in high quality healthy lighting.This paper aims to obtain a high-continuity full-spectrum white LED,focusing on developing high-performance red and cyan fluorescent phosphors for NUV LED.The main research work and results are as follows:（1）In view of the lack of high-performance red phosphor in NUV LED,a series of Sc PO₄:Eu³⁺,Tb³⁺phosphors were synthesized.The samples has a tetragonal crystal structure with evenly distributed particles and a smooth"elliptic"morphology.With the increasing doping concentration of Tb³⁺,Tb³⁺gradually transmits energy to Eu³⁺,and the emission peak intensity corresponding to Tb³⁺decreases,and the characteristic red light emission peak intensity of Eu³⁺shows a trend of increasing first and then decreasing.The mechanism of energy transfer is determined by the fluorescence decay curve and the electron transition level.The Sc_0.84PO₄:0.07Eu³⁺,0.09Tb³⁺energy transfer efficiency is 42.22%,and the energy transfer between Tb³⁺-Eu³⁺is dominated by the electric multistage interaction of dipole-dipole.Changing the Tb³⁺-Eu³⁺ratio changes the luminous color region from orange-red（0.4357,0.3402）to yellow（0.4107,0.3948）.The white light LED device with the phosphor of yellow（0.4107,0.3948）luminous color region has a higher color display index（Ra=88.6）and a lower color temperature（CCT=3470 K）.In addition,Li⁺ions were introduced into the Sc PO₄matrix to form a new matrix material,Li₃Sc₂（PO₄）₃,and further doped with Eu³⁺ions to synthesize the excellent performance of Li₃Sc₂（PO₄）₃:Eu³⁺new red phosphor.Eu³⁺enters the main lattice in the Li₃Sc₂（PO₄）₃matrix instead of the Sc³⁺position.The phosphor has a polyhedral morphology and a uniform particle distribution,with an average particle size of about 20μm.The phosphor has bright red emission and the strongest emission peak is located at 612 nm,indicating that Eu³⁺mainly occupies the lattice site with inversion symmetry.The optimal doping concentration of Eu³⁺is 0.35 mol,and the concentration-quenching mechanism is a dipole-dipole interaction.The fluorescence lifetime of Li₃Sc_1.65（PO₄）₃:0.35Eu³⁺is 2.820 ms,and its red light color purity is as high as 87%.When the temperature rises to 423 K,the relative emission intensity of the sample remains 75.5%at room temperature,showing good thermal stability.（2）Ca₂Sr（PO₄）₂:Eu³⁺and Ca₂Sr（PO₄）₂:Mn²⁺red phosphors excited by Eu³⁺and Mn²⁺were synthesized based on the diamond structure ofβ-Ca₃（PO₄）₂matrix material.The introduction of Li⁺ions further improves the luminescence performance of Ca₂Sr（PO₄）₂:Eu³⁺.Li+ions can enter the main lattice in the form of Ca²⁺lattice substitution and entry gap,respectively,but it does not change the original structure of the sample,and it can reduce the agglomeration phenomenon between particles.Ca₂Sr（PO₄）₂:Eu³⁺,Li⁺samples can emit bright red light under NUV excitation.Li⁺doping hardly changes the excitation and emission spectra of the sample,but it can improves the relative luminescence intensity of the sample,which is related to the Li⁺modifying the surrounding local crystal field environment of Eu²⁺after entering the lattice and replacing the introduced oxygen vacancy as a sensitizer.In addition,Li⁺ions acting as a flux also reduces the impurity content of the loud son energy,thus increasing the luminescence intensity of the sample.The Li⁺optimal doping concentration was 0.04 mol,Ca_1.91Sr（PO₄）₂:0.05Eu³⁺,0.04Li⁺lifetime was 0.4695 ms.The CIE coordinate of（0.6635,0.3339）is located in the red light area,and it has good moisture resistance,alkali resistance,chemical stability energy and excellent thermal stability energy(I_423K=72.38%).In addition,the Mn²⁺-excited Ca₂Sr（PO₄）₂:Mn²⁺phosphor has broad-band red light emission,Mn²⁺to replace the Ca5 position of Ca²⁺into the main lattice,and the wide direct bandgap width（3.78 e V）of the Ca₂Sr（PO₄）₂is capable of accommodating the Mn²⁺electron level.Mn²⁺optimal doping concentration is 0.03 mol,excited in NUV region,Ca_1.97Sr（PO₄）₂:0.03Mn²⁺sample emits broadband red light（FWHM=93 nm）at 628 nm,color purity up to 92.4%,and has good thermal stability(I_{473 K}=61.5%).The color development index of the white WLED device package reached 86.9,and the lumen efficiency hardly changes with the long working time.（3）In view of the blue green light"gap"in the WLED spectrum,the new Ca₉Na（PO₄）₇was selected as the matrix material,and the Ca₉Na（PO₄）₇:Eu²⁺cyan phospfors material excited by Eu²⁺was synthesized by the NUV LED.The doping of Eu²⁺did not change the sample rhombic crystal system structure,and the sample particles had an irregular morphology with a mean particle size of10–15μm.The[Ca Ox]polyhedron in the Ca₉Na（PO₄）₇matrix provides favorable conditions for the introduction of Eu²⁺.Ca₉Na（PO₄）₇:Eu²⁺phospfor can be excited at 491 nm,its concentration quenching effect comes from the multipole-multipole interaction,the optimal Eu²⁺doping concentration is 0.8 mol.The fluorescence life of the Ca_8.2Nd（PO₄）₇:0.8Eu²⁺sample is 51.10s,and the thermal activation energy（0.2698 e V）shows an excellent thermal stability(I_{373 K}=84.75%).The spectrum emitted from the WLED device packaged in Ca₉Nd（PO₄）₇:Eu²⁺phosphor covers almost the entire visible region,with a color rendering index of 95.7 and all R1-R15 greater than 90.Therefore,Ca₉Nd（PO₄）₇:Eu²⁺phosphor can be used to fill the blue green light"gap"in the WLED spectrum.So Ca₉Nd（PO₄）₇:Eu²⁺phosphor is a potential blue green fluorescence material used in WLED.