Study On The Structure And Luminescent Properties Of Cr³⁺ Doped Ca₂LuHf₂Al₃O₁₂ Near-infrared Phosphors

Broadband near-infrared light near 800 nm has promising application prospects in food testing and night vision monitoring.Compared with near-infrared chips,near-infrared phosphors have advantages like lower cost,mature synthesis technology,and combinable tuning spectrum.However,near-infrared phosphors generally have shortcomings such as narrow full width at half maximum(FWHM),poor thermal stability,and weak emission intensity,which limit the commercial application of near-infrared phosphors.The classic garnet structure features good stability and three different polyhedron environments,which make the broadband emission of Cr3+ possible.Therefore,we synthesized Cr3+ doped garnet structure broadband near-infrared phosphors,and improve the emission intensity of near-infrared phosphors by energy transfer.In addition,based on the flexibility of garnet structure phosphors and various luminescent properties of Cr3+ in different crystal environments,we attempted to adjust the luminescent properties of Cr3+ through composition substitution.The luminescent properties of Ca2LuHf2Al3O12:Cr3+ has been studied.Under 460 nm excitation,Ca2LuHf2Al3O12:Cr3+shows a broadband emission peak at 775 nm(FWHM=147 nm).The concentration quenching of Cr3+in Ca2LuHf2A13O12 matrix is caused by radiation reabsorption and dipole-dipole interaction according to analyzing the excitation spectrum and emission spectrum and the relationship between log(I/x)and log(x).The emission peaks of Ca2LuHf2Al3O12:xCr#+(x=0.01～0.1 1)shift to longer wavelength may be ascribed to radiation reabsorption and multipole interaction.Under 460 nm excitation,the emission intensity of Ca2LuHf2Al3O12:0.03Cr3+ at 150℃ is 80.29%of the initial intensity measured at room temperature,which indicates that Ca2LuHf2Al3O12:Cr3+ is a promising broadband NIR phosphor.Energy transfer from Ce3+to Cr3+has been created in Ca2LuHf2Al3O12 matrix in order to enhance the emission intensity of Cr3+.Under the excitation of 405 nm,the near-infrared emission intensity of Ca2LuHf2A13O12:0.03Cr3+,0.03Ce3+can be enhanced by three times comparing to that of Ca2LuHf2Al3I12:0.03Cr3+ due to the energy transfer from Ce3+ to Cr3+,which can be evidenced by two reasons.Firstly,there is a significant spectrum overlap between the excitation spectrum of Ca2LuHf2Al3O12:Cr3+ and the emission spectrum of Ca2LuHf2Al3O12:Ce3+.Secondly,the lifetime of Ce3+decreases with Cr3+ concentration increasing in Ca2LuHf2A13O12:xCr3+,0.03Ce3+(x=0.01-0.07).The mechanism of energy transfer is identified as a quadrupole-quadrupole interaction according to decay lifetime and Dexter’s theory.The emission intensity of Ca2LuHf2Al3O12:0.03Ce3+,0.03Cr3+at 150℃ is 55.58%of the initial intensity measured at room temperature.According to the composition adaptability of the garnet structure,we turned luminescent properties of Cr3+ based on Ca2LuHf2Al3O12 by composition substitution.Firstly,we synthesized Ca2AHf2Al3O12:0.03Cr3+(A=La,Gd,Y,Lu)phosphors.Under the excitation of 460 nm,the emission peak of Cr3+ shift to longer wavelength from 775nm to 800nm when A substituted from Lu to La.The red shift of Ca2AHf2Al3O12:0.03Cr3+(A=La,Gd,Y,Lu)phosphors caused by decreasing crystal field strength due to the enlarged octahedron.Secondly,on the basis of Ca2LuHf2Al3O12,series phosphors including Y3Sc2Al3O12:Cr3+,Lu3Sc2Al3O12:Cr3+,Ca2LuSc2Ge2AlO12:Cr3+ and Ca3Sc2Ge3O12:Cr3+were obtained via non-equivalent con-substitution.Under the excitation of 460 nm,Y3Sc2Al3O12:0.03Cr3+,Lu3Sc2Al3O12:0.03Cr3+ feature narrowband emission peak at 689 nm(FWHM=30 nm),Ca3Sc2Ge3O12:0.03Cr3+ features broadband emission peak at 780 nm(FWHM=101 nm),and Ca2LuSc2Ge3O12:0.03Cr3+ features broadband emission peak at 805 nm(FWHM=153 nm).