Structure And Luminescence Properties Of Sm³⁺?Eu²⁺ Doped With Sr₂Al₂SiO₇ Phosphors

In this paper,the crystal structure and luminescence properties of Sr_2-xAl₂SiO₇:x%Sm³⁺orange red phosphor,Sr₂Al₂SiO₇:R⁺,Sm³⁺(R=Li?Na?K)phosphorand Sr_1.98(Al_1-xMg_x)(Al_1-xSi_1+x)O₇:2%Eu²⁺:Crystal structure and luminescence properties of2%Eu²⁺phosphor.Crystal structure,morphology,luminescent properties,color coordinates,etc.of the the preparation of the phosphor were discussed in detail.(1)A series of Sr_2-xAl₂SiO₇:x%Sm³⁺orange-red phosphors were prepared by high-temperature solid state reaction.The crystal structure and luminescence properties of the samples were analyzed by X-ray powder diffraction,morphology and photoluminescence spectroscopy.The results show that Sm³⁺is doped into the Sr_2-xAl₂SiO₇ matrix and replaces the Sr²⁺lattice.Due to the different ionic radius,the XRD diffraction peak shifts to a large angle,and the crystal structure changes slightly,but the morphology does not have much influence.There are no rules for the size of the appearance.When the doping concentration of Sm³⁺ions reaches 2%,concentration quenching occurs,and the critical distance is determined by the critical distance formula to be 19.73?,and further calculated by Dexter formula to obtain multi-level interaction function?=6,concentration between Sm³⁺The extinction mechanism is a galvanic-electron-level interaction.(2)A series of Sr₂Al₂SiO₇:R⁺,Sm³⁺(R=Li,Na,K)phosphors were successfully synthesized by high temperature solid phase method.The effects of doped metal ions Li⁺,Na⁺and K⁺on the crystal structure and photoluminescence spectrum of Sr₂Al₂SiO₇:Sm³⁺phosphors were investigated.The results show that the charge compensators Li⁺,Na⁺,K⁺and Sr²⁺have different ionic radii,and the XRD diffraction peaks are shifted.Because the doping charge compensator Li⁺,Na⁺,K⁺balances the internal charge of the crystal,the luminescence intensity is improved compared with the absence of the charge compensator,and the order of arrangement is I_Li>I_k>I_Na,when both Sm³⁺and Li⁺concentrations are 2%,the sample has the highest luminous intensity.Under the excitation of near-UV 403 nm wavelength,the emission peak is generated by the energy level transition of Sm³⁺⁴G_5/2?⁶H_J/2(J=5,7,9,11),and the emission intensity at 601 nm is the largest,which makes orange-red fluorescence.Sr_1.96Al₂SiO₇:2%Li⁺,2%Sm³⁺fluorescence pink coordinates(0.60,0.39),high color purity is about 92.5%,quantum efficiency is 43.6%,indicating that the red component of the phosphor in the trichromatic white LED has application potential.(3)A series of Sr_1.98(Al_1-xMg_x)(Al_1-xSi_1+x)O₇:2%Eu²⁺phosphors is prepared by the high-temperature solid-state reaction method,the crystal structures and luminescent properties of the prepared phosphors were investigated by the measure of the X-ray diffraction,luminescent spectra and optical microscope.Isomorphic compounds of Sr₂Al₂SiO₇ and Sr₂Mg Si₂O₇ contain of tetrahedral including[Mg O₄],[SiO₄]and[Al O₄].Although the valences of the[Mg O₄]^6-,[SiO₄]^4-and[Al O₄]^5-groups are different,but the charge imbalance occurs when the[Mg O₄]^6-and[SiO₄]^4-substitutes of[Al O₄]^5-and[Al O₄]^5-,respectively.While the groups are co-substitution,the charge imbalance was disappeared.And the larger volume of[Mg O₄]and the smaller volume of[SiO₄]together replaced the similar volume of[Al O₄],resulting in decreasing of[(Si/Al)O₄]and increasing of[(Mg/Al)O₄].Moreover,the decreasing of unit the cell parameters c,increasing of a and V due to the increased replacement of Mg²⁺(0.57?for CN=4)by Al³⁺(0.39?for CN=4)and Si⁴⁺(0.26?for CN=4)by Al³⁺(0.39?for CN=4).The crystal field splitting of the Eu²⁺cation to be weakened.and the emission spectra are blue shifted from 503 nm to 467 nm are closely related to the local coordination environment of the Eu²⁺,in addition,this reveals that the emission color of this series of phosphors can be tuned from green with color coordinate(0.2384,0.3919)to blue(0.1342,0.1673)by adjusting the chemical compositions via the[Mg O₄]^6-?[SiO₄]^4-groups co-substitution for[Al O₄]^5-.The half maximum(fwhm)of emission band is 120 nm when x=0,the PL emissionwidth decrease monotonically from 89 to 50 nm as x is increased from 0.25 to 1.In other words,the full width at fwhm of emission band exhibits a decreasing trend.Internal quantum efficiency of the higher with increasing x in Sr_1.98(Al_1-xMg_x)(Al_1-xSi_1+x)O₇:2%Eu²⁺phosphors.These results verify that the groups con-substitute are enhanced with polyhedron changes inthe solid solutions and contribute largely to the luminescence properties of the phosphor.