Spectral Control Of Mg₂Y₂Al₂Si₂O₁₂ Host Phosphor Based On Lattice Substitution And Energy Transfer

In this paper,a series of transition metal ions Mn²⁺ and rare earth ions Eu²⁺/Ce³⁺single-doped or co-doped Mg₂Y₂Al₂Si₂O₁₂-based phosphors are synthesized by high temperature solid phase method.The spectral shift and performance improving of the sample materials are achieved by multi-site substitution and concentration adjustment of the single-doped activated ions,as well as energy transfer of the co-doped activated ions.The luminescence properties of the materials are studied and analyzed by various characterization methods.Finally,single-doped phosphors with adjustable color of emitted light,warm white phosphors with near-ultraviolet excitation and red compensation powders with high quantum efficiency for white LEDs are obtained.The results of the specific study are as follows:（1）Firstly,Mg_2-xY₂Al₂Si₂O₁₂:xMn²⁺single-doped phosphors are synthesized.By using the unique crystal structure of{Y₂Mg}[MgAl]（AlSi₂）O₁₂ host in which different ions occupy the same position and in which the same ion occupies different positions,Mn²⁺ has been successfully doped into the crystal structure of the host,replacing Mg²⁺ at eight-coordinated,Mg²⁺ at six-coordinated and Al³⁺at four-coordinated,forming three luminescent centers:Mnl,Mn2 and Mn3.The red,near infrared and green light emissions are obtained from the multi-site luminescence in the garnet structure.In addition,by adjusting the doping concentration of Mn²⁺,the emission spectra shift from green to near infrared under the fixed excitation of a single host.Based on the theories of crystal field splitting and lattice distortion,the emission spectra shift mechanism of Mnl,Mn2 and Mn3 with doping concentration is analyzed in detail.Finally,the temperature stability of Mg_2-xY₂Al₂Si₂O₁₂:xMn²⁺ single-doped phosphors is investigated and analyzed.（2）A series of phosphors of Mg₂Y_2-yAl₂Si₂O₁₂:yEu²⁺,Mg₂Y_2-yAl₂Si₂O₁₂:yEu²⁺、Mg_2-xY_1.99Al₂Si₂O₁₂:xMn²⁺,0.01Eu²⁺are synthesized by selecting Eu²⁺ as the sensitizing ion.Firstly,Eu²⁺ does replace Y³⁺non-equivalently,which affects the garnet structure of the samples,and then the internal environment of the crystal affects the energy level splitting of Eu²⁺,which causes the emission spectra of Mg₂Y_2-yAl₂Si₂O₁₂:yEu²⁺ phosphors red shift 70nm from 425nm to 495nm.Secondly,the optimal doping concentration of Eu²⁺ is selected and the energy transfer of Eu²⁺ to Mn²⁺ is used by co-doping Eu²⁺ and Mn²⁺,to realize the color continuous adjustment of the phosphor from blue to white.Finally,the color coordinate of Mg_1.4Y_1.99Al₂Si₂O₁₂:0.6Mn²⁺,0.01Eu²⁺ is detected as（0.3254,0.2669）in the white light region,and the color temperature of Mg_1.4Y_1.99Al₂Si₂O₁₂:0.6Mn²⁺,0.01Eu²⁺ is 5791.19K.The single-host warm white light-emitting phosphor with near-ultraviolet-excited is obtained.（3）Firstly,Mg₂Y_2-zAl₂Si₂O₁₂:zCe³⁺,Mg_2-xY_1.93Al₂Si₂O₁₂:0.07Ce³⁺,xMn²⁺ phosphors are synthesized by high temperature solid phase method.The excitation spectra and emission spectra properties of Ce³⁺ 5d1 and 5d2 levels in the Mg₂Y_2-zAl₂Si₂O₁₂:zCe³⁺ samples are studied in detail.That Ce³⁺ replaces Y³⁺ results in an increase in lattice distortion,causing the 405nm emission peak at 323nm excitation and 600nm emission peak at 470nm excitation both move in the direction of long wave.The effects of the energy transfer of Ce³⁺to Mn²⁺and the doping of Mn²⁺ on the Ce³⁺ luminescence environment realize that the emission peak of Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺ moves toward the long-wave direction,effectively increasing the red component of the emission spectra.At low concentration doping,the entry of Mn²⁺ ions increases the distance between Ce³⁺ions,reduces the number of Ce³⁺ ion quenching centers,enhances the emission intensity of Ce³⁺ ions,as a result that the emission intensity of Mg_2-xY_1.93Al₂Si₂O₁₂:0.07Ce³⁺,xMn²⁺ phosphors abnormally enhances comparing with the emission intensity of the Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺ phosphor.The experiment successfully obtained Mg_1.97Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,0.03Mn²⁺ sample with excitation wavelength at 470nm and emission peak at 618nm,which can well compensate the red component of blue chip+yellow phosphor mode white LED.Finally,the quantum eff-iciency of the sample is detected as 83.07%,accord with the level of commercial application.