Preparation And Properties Of Cr³⁺-Doped Gadolinium Gallium Aluminum Garnet Near Infrared Ceramic Phosphor

Near-infrared（NIR）light detection technology has many advantages such as rapid response,non-destructive testing,pollution-free testing,etc.,and is widely used in the fields of thermal therapy,agricultural and sideline products testing,food and drug identification,brain function imaging,tumor targeted localization and biosafety identification.With the popularity of portable handheld intelligent terminals and the increasing attention paid to healthy living and eating,small and even micro near-infrared detectors have gradually become a new development trend.However,how to achieve miniaturization of near-infrared light sources,taking into account the high efficiency and wide emission characteristics of the light source in a limited space is still a challenge.The traditional near-infrared light source with tungsten halogen lamp has defects such as high working temperature,low luminous efficiency,short life,etc.,while near-infrared light-emitting diodes（NIR-LED）have the problem of narrow emission spectrum,which cannot meet the application needs of near-infrared light sources.Therefore,the development of new efficient,stable and wideband emission NIR light-emitting materials and the exploration of suitable packaging processes to meet the needs of portable NIR detection have become the focus of researchers.In view of this demand,this paper proposes a wideband emitted fluorescent ceramic preparation and performance study that can achieve high-power near-infrared fluorescence output.Gadolinium gallium aluminum garnet(Gd₃Al_xGa_5-xO₁₂,hereinafter referred to as GAGG)is selected as the matrix and Cr³⁺is used as the center of luminescence.Firstly,the precursor powder is prepared by chemical co-precipitation,and then the highly dense GAGG:Cr NIR ceramic phosphor is obtained after calcination,blank molding and high-temperature sintering.By adjusting the crystal field and optimizing the concentration of luminescent ions,the luminous efficiency and thermal stability of the material are significantly optimized.The near-infrared light source device based on this ceramic sample has achieved breakthroughs in electro-optical conversion efficiency and optical output power.The specific research contents and results are as follows:（1）Effects of crystal field adjustment of GAGG:Cr³⁺NIR ceramic phosphor on luminescence properties.According to the energy band engineering theory,GAGG:Cr³⁺with different Al/Ga proportional components is designed.Under the excitation of 445 nm blue light,it emits broadband NIR from 650-900 nm.When the Al/Ga ratio is 2:3,the comprehensive performance of luminous efficiency and thermal stability is the best,and the external quantum efficiency can reach up to 65%.Based on the best component ceramic samples,a near-infrared ceramic phosphor converted LED device（NIR cpc-LED）was preliminarily packaged with a commercial blue LED chip,and a near-infrared light output power exceeding the watt level was achieved.The results show that the matrix composed of Gd₃Al₂Ga₃O₁₂ can provide a suitable crystal field for Cr³⁺,in which Cr³⁺can be effectively excited to achieve broadband emission of near-infrared light.（2）Optimization of luminous efficiency of GAGG:x Cr³⁺NIR ceramic phosphor and its application in vein imagingBased on the determination of the matrix composition,the luminous efficiency of GAGG:x Cr³⁺NIR ceramic phosphor was further optimized by adjusting the Cr³⁺doping concentration.When x=0.075,the internal quantum efficiency（IQE）of the best sample is close to 100%,the external quantum efficiency（EQE）is as high as 70.1%,and its luminescence intensity can still be maintained at 96.8%of the room temperature intensity at 150°C.The best ceramic samples were packaged with miniature blue LED chips into devices,achieving broadband near-infrared light output from 650-900 nm.When the driving current is 20 m A,the electro-optical conversion efficiency of the device is as high as 31%.In addition,under the excitation of the high-power LD chip,the luminescence saturation threshold of the device can reach 7 W m^-2,and the NIR output power is as high as 1652.6 m W.The related devices realize palmar vein resolution imaging,and the maximum spatial resolution can reach 1 mm.These results are significantly higher than previously reported Cr³⁺fluorescence conversion materials,indicating that GAGG:Cr³⁺NIR ceramic phosphor have strong advantages in the application of high-power near-infrared light sources.