Preparation And Luminescence Mechanism Of Garnet Phosphors For White-LEDs

White light emitting diodes have increasingly drawn widespread attention due to their high luminous efficiency,long lifetime,energy saving and environmental friendliness.As one of the core part in WLED,the development of novel phosphor has important academic significance and practical application.In general,there are two strategies（cation substitution and co-doping activators）to enhance the red emission of YAG:Ce³⁺system,for the purpose of high CRIs and low CCTs.The aim of this thesis is to synthesize garent phosphors by double-doping or multi-doping luminescent activators for ultraviolet or blue chip pumped white LEDs.The main contents of this thesis are as follows:1.MgY₂Al₄SiO₁₂:Eu²⁺,Ce³⁺has been synthesized by solid state reaction,and its garnet structure was confirm by XRD.Under the excitation of 340 nm,the phosphor exhibits two emission bands peaking at 445 nm and 565 nm,which correspond to the4f⁶5d→4f⁷ transition of Eu²⁺and 5d→4f transition of Ce³⁺,respectively.The results show that the energy transfer mechanism belongs to dipole-dipole interaction.The chromaticity coordinates of the obtained phosphor is tunable by varying the concentration of Eu²⁺and Ce³⁺.When the doping concentraction of Eu²⁺and Ce³⁺were0.01 and 0.06,respectively,the color coodinates of phosphor is（0.285,0.345）.2.MgY₂Al₄SiO₁₂:Ce³⁺,Mn²⁺has been synthesized,and its garnet structure was confirm by XRD,furthermore,Mn²⁺was clearly defined to be doped in the dodecahedral Mg²⁺site by XPS and Crystal Rietveld refinement.Under the excitation of 460 nm,the phosphor exhibits two emission bands peaking at 565 nm and 620 nm,which correspond to the 5d→4f transition of Ce³⁺and transition d→d of Mn²⁺,respectively.The results show that the energy transfer mechanism belongs to dipole-quadrupole interaction.The chromaticity coordinates of the obtained phosphor is tunable by varying the concentration of Ce³⁺and Mn²⁺.As the doping content of Mn²⁺increasing from 0 to 0.15,Mn²⁺related red emission is enhanced systematically,and emitting color of phosphor was found to shift from yellow toward orang-red region.MgY₂Al₄SiO₁₂:Ce³⁺,Mn²⁺is a color tunable phosphor for blue light chips to obtain warm white LED.3.MgY₂Al₄SiO₁₂:Eu²⁺,Ce³⁺,Mn²⁺has been synthesized,and its garnet structure was confirm by XRD.Under the excitation of 340 nm,the phosphor exhibits three emission bands with Eu²⁺（445 nm）,Ce³⁺（565 nm）,Mn²⁺（620 nm）emission,and the emission spectra almost covers the whole visible region The chromaticity coordinates of the obtained phosphor is tunable by varying the concentration of the three luminescent activators.The color coodinates of Mg_0.93Y_1.94Al₄SiO₁₂:0.01Eu²⁺,0.06Ce³⁺,0.06Mn²⁺and Mg_0.9Y_1.94Al₄SiO₁₂:0.01Eu²⁺,0.06Ce³⁺,0.09Mn²⁺are（0.333,0.343）,（0.349,0.339）,respectively,which are close to the white lighting（0.333,0.333）.MgY₂Al₄SiO₁₂:Eu²⁺,Ce³⁺,Mn²⁺is a tunable single host white light emitting phosphor for ultraviolet chip pumped white LEDs.