Preparation And Performance Regulation Of Rare Earth Ions Doped Sr_0.8Ca_0.2Al₂Si₂O₈ Phosphors For Near-ultraviolet White LEDs

A series of Eu²⁺,Ce³⁺and Tb³⁺ions doped Sr_0.8Ca_0.2Al₂Si₂O₈ phosphors were successfully prepared by a high-temperature solid-state reaction.The effects of substitution priority,host regulation and energy transfer on luminescence are systematically studied,and the reasons are carefully investigated.The results as follows:?1?A series of blue-emitting Sr_0.8Ca_0.2Al₂Si₂O₈:Eu²⁺phosphors are synthesized.The substitution priority of Eu²⁺in Sr_0.8Ca_0.2Al₂Si₂O₈ was investigated by XRD,emission spectra,temperature properties and fluorescent decay curves.The results indicates that Ca²⁺ions are preferentially substituted by Eu²⁺at lower doping,and with the Eu²⁺ concentration increasing,the probability of substitution for Sr²⁺is greater than that of replacing Ca²⁺.Moreover,the emission spectra show a red-shift with increasing Eu²⁺ ions under ultraviolet light excitation,as the same time,the half tall full width of ?FWHM?of the emission spectra widens gradually.As the result,the emission changesfrom deep blue to light blue,which should be attributed to result crystal field splitting and energy transfer from Eu²⁺ions at higher energy to Eu²⁺ions at lower energy Eu²⁺.A series of warm white light emitting diodes were successfully fabricated using the blue phosphors Sr_0.8Ca_0.2Al₂Si₂O₈:Eu²⁺with commercial red phosphor and green phosphor, and the luminescent efficiency can reach 45 lm/W.?2?Two methods for Sr_0.8Ca_0.2Al₂Si₂O₈:Eu²⁺phosphors that were performed to optimize the luminescence properties and thermal stability based on structural reconstruction.One is partialsubstitutionofAl–SrbySi–NaformingSr_0.77-yNa_yCa_0.2Al_2-ySi_y²⁺O₈: 0.03Eu²⁺?y=0⁰.7?;the other is altering the proportion of Ca²⁺and Sr²⁺,forming Sr_0.97-zCa_zAl₂Si₂O₈:0.03Eu²⁺?z=0¹?solid solution.The XRD,emission spectra, temperature spectra,lifetime decay curves and quantum yield of two series are studied in detail.The results indicate that neither two methods will affect the phase purity,while all of them can cause a red-shift of emission.And more notably,for the first method,the thermal stability of samples is improved with increasing Si–Na;for the second method, the temperature stability of the sample when Ca²⁺and Sr²⁺coexist is higher than the thermal stability of CaAl₂Si₂O₈:0.03Eu²⁺and SrAl₂Si₂O₈:0.03Eu²⁺.These show that the regulation of matrix components is an effective way to improve the temperature stability of the phosphor.The research results show that the luminescent material with adjustable color,stable temperature characteristics and high quantum efficiency can be obtained through matrix control.?3?Ce³⁺ion doped Sr_0.8Ca_0.2Al₂Si₂O₈ phosphors and Sr_0.8Ca_0.13Al_2+gSi_2-gO₈:0.07Ce³⁺?g=0⁰.7? phosphors are synthesized.The characteristics of luminescence of Ce³⁺ions and the effect of Al partly replace Si are investigated by XRD,emission spectra and lifetime decay curves.The results indicate that the Ce³⁺ion show blue-emitting in Sr_0.8Ca_0.2Al₂Si₂O₈ host.With the substitution of Si by Al,the unit cell gradually expands which result the relaxation of local environment of Ce³⁺ion,the decrease of 5d energy level splitting and reduction of efficient luminescence centers.As a result,the emission spectra of the samples show a blue shift,a narrower half-width,and increased emission peak intensity.The results above are of great significance for obtaining suitable blue phosphor for display.?4?A series of Eu/Tb doped Sr_0.8Ca_0.2Al₂Si₂O₈ phosphors are synthesized.The luminescence and energy transfer of Eu²⁺,Tb³⁺,Eu³⁺ions are explored by excitation spectra,emission spectra,and lifetime decay curves.The results indicate that Eu²⁺and Eu³⁺coexist when Eu-doped Sr_0.8Ca_0.2Al₂Si₂O₈ phosphors are synthesized under air atmosphere and Tb³⁺ ions present green emitting in this matrix.There is no characteristic emission of Tb³⁺ ions in the emission spectrum of the Sr_0.8Ca_0.2Al₂Si₂O₈:Eu,Tb sample synthesized in the atmosphere.However,the emission spectra of Tb³⁺ions appeared in the emission spectra of Sr_0.8Ca_0.2Al₂Si₂O₈:Eu,Tb samples synthesized under the reducing conditions.The reason should be that there are two forms of energy transfer:energy transfer from Eu²⁺to Tb³⁺,and energy transfer from Tb³⁺to Eu³⁺ions.The latter's energy transfer efficiency is much greater than the former.When Eu²⁺,Tb³⁺,and Eu³⁺exist at the same time,the energy transfer form of Eu²⁺?Tb³⁺?Eu³⁺appears.This result is of great significance for changing the luminescent properties of phosphors based on energy transfer.