Preparation And Luminescence Properties Of Several Red And Near Infrared Phosphors

Phosphor-converted LEDs(pc-LEDs)are widely used in lighting,medical,display,plant lighting and other fields resulting from their high energy conversion and utilization efficiency,environmentally benign,long service life,and suitable size.pc-LED is mainly composed of LED chips and one or more phosphors,and the photoluminescence color changes with the coated phosphors.Therefore,inorganic light-emitting materials,which are important components,have been extensively studied.In recent years,a variety of phosphors with excellent properties have been obtained in the wavelength range covering the visible to near-infrared region.In addition,due to the characteristics of spectral modulation(absorbing short-wavelength light and emitting long-wavelength light),near-infrared phosphors can be used in crystalline silicon solar cells as a solar spectrum converter to absorb short-wavelength sunlight that cannot be effectively utilized by solar cells and convert into 950-1100 nm near-infrared light.This can improve the photoelectric conversion efficiency of solar cells.In this dissertation,we obtained several red or near-infrared phosphor materials that can be efficiently excited by near-ultraviolet or blue light.Through corresponding testing and characterization methods,the phase structure,ionic substitution site,spectral properties and application value of the samples were systematically studied.The specific content includes the following parts:(1)Eu3+-doped LiYO2 red phosphors were synthesized that can be efficiently excited by near-ultraviolet light.The phase purity,crystal structure and ion occupation of the samples were fully discussed by XRD,structure refinement and scanning energy spectroscopy.LiYO2:Eu3+has relatively weak charge transfer band and strong 4f-4f transition.By comparing the emission spectra,it can be seen that the wavelength at 395 nm can produce the maximum emission intensity.Under excitation at 395 nm,the sample produces bright red emission with a color purity of over 98%.Meanwhile,the samples have excellent luminescence thermal stability.Finally,the white LED device with excellent performance was prepared,indicating that the sample has potential application value.(2)Bi3+ doped and Bi3+,Eu3+codoped Y3GaO6 phosphors were prepared by high temperature solid state method.Bi3+ions have two different Y sites in the matrix that can be occupied,and the site occupancy preference is driven by the concentration of Bi3+ions.When the doping concentration is low,Bi3+ions occupy the Y1 site,showing a blue-violet emission with a peak of 410 nm;at high concentration,Bi3+ions mainly occupy the Y2 site and exhibit orange-yellow luminescence.As the concentration changes,the emission color gradually changes from blue-violet to orange-yellow.In addition,the energy transfer phenomenon from Bi3+to Eu3+is also studied in detail.Y3GaO6:Bi3+and Y3GaO6:Bi3+,Eu3+have high quantum efficiency and excellent luminescence thermal stability.The possibility of sample application in WLED is demonstrated by the packaged white LED device.(3)The Mn4+-doped double perovskite structure luminescent material with high-efficiency red emission was prepared.Mn4+ ions are incorporated into the matrix by replacing Sb5+ ions.Under the excitation of near-ultraviolet light,the sample exhibits deep red emission,and the position of the emission band has a large overlap with the absorption of the plant photosensitive protein Pfr,demonstrating that the sample is a potential candidate for plant growth LEDs.The quantum efficiency of the Sr2InSbO6:Mn4+ sample is as high as 55.93%.Moreover,the obtained samples have good thermal stability.In addition,the crystal phase and luminescence of Ca2(1-z)Sr2zInSbO6:Mn4+ samples was investigated in detail by Sr substitution of Ca.Finally,a warm white light with better performance was obtained using the optimal sample.(4)The LaGaO3:Cr3+,Ln3+(Ln=Yb,Nd,Er)near-infrared luminescent material was designed and synthesized.The crystal structure and phase purity of the obtained samples were analyzed by XRD,structure refinement and SEM energy spectroscopy.The luminescence,Cr3+→Ln3+(Ln=Yb,Nd,Er)energy transfer,and energy transfer efficiency of the samples were analyzed by spectra and fluorescence lifetime.In addition,we also briefly discuss the energy transfer phenomenon of Nd3+/Er3+→Yb3+in the host.Comparing the excitation and emission spectra of the sample with the solar spectrum and the response curve of the crystalline silicon solar cell,it can be seen that the sample can absorb short-wave light in the ultraviolet-visible region and effectively emit near-infrared light around 1000 nm,indicating that the sample has the ability to convert light as a crystalline silicon solar cell.The application value of the material.(5)A broadband BaZrGe3O9:Cr3+near-infrared phosphor was successfully obtained by replacing Zr4+ with Cr3+.Under blue excitation,the sample displays broadband near-infrared light covering 650 to 1100 nm,with full width at half maximum～160 nm,indicating that Cr3+ions occupy a weak crystal field environment.Due to the substitution of Cr3+ for Zr4+ is an unequal substitution,it will cause the charge imbalance of the sample,resulting in defects that affect the luminescence.We balance the charges by introducing alkali metal ions(Li+,Na+,K+)into the samples as charge compensators.The results showed that the incorporation of alkali metal ions greatly improved the luminescence intensity and thermal stability of the samples.Therefore,the obtained broadband near-infrared phosphors have application value in near-infrared LEDs.