Synthesis And Properties Of Cr³⁺Doped Silicate Based Broadband Near Infrared Luminescence Materials

Compared with traditional near-infrared light sources,phosphor-converted near-infrared LED(pc-NIR LED)has many advantages,such as high luminous efficiency,small size,simple manufacturing process,and low cost.These characteristics make pc-NIR LED have broad application prospects in night vision monitoring,biological tissue imaging,industrial nondestructive testing and other fields.Phosphors,as key materials in pc-NIR LEDs,play a decisive role in the overall performance of near-infrared LED devices.In recent years,Cr3+iondoped broadband light-emitting materials have attracted extensive attention of scholars at home and abroad due to their superior near-infrared luminescence properties.Among them,Cr3+iondoped silicate broadband near-infrared light-emitting materials have the advantages of good physical and chemical stability,low cost and high luminous efficiency,and are expected to be ideal light conversion materials for pc-NIR LEDs.This paper focuses on the design,preparation and properties of Cr3+-doped silicate-based wideband near infrared luminescence materials.The main research contents and results of this paper are as follows:(1)A series of Cr3+-doped BaMSi3O9(M=Zr,Sn,Hf)near-infrared emitting phosphors with tunable luminescence properties have been successfully synthesized by using a simple solid-state reaction method.The developed BaMSi3O9:Cr3+phosphors show broad NIR emission band ranging from 650 nm to 1200 nm with peak wavelength longer than 800 nm and a full width at half maximum(FWHM)of more than 155 nm upon blue light excitation.The critical concentration of Cr3+are determined to be 0.5%,1%and 3%in BaZrSi3O9:Cr3+,BaSnSi3O9:Cr3+and BaHfSi3O9:Cr3+systems,respectively.The optimized phosphor also demonstrates good thermal stability,whose emission intensity at 125℃ can maintain at about 66%of its initial.intensity at room temperature.The NIR LED prototypes constructed by combining the BaMSi3O9:Cr3+phosphor with blue LED chip give a maximum NIR output power of 12.2 mW at a drive current of 320 mA.By using the fabricated NIR LED device as lighting source,night-vision lighting and blood vessel imaging of human fingers and arms are successfully realized,demonstrating the great potential of BaMSi3O9:Cr3+phosphors for NIR LED applications.(2)A series of Na3ScSi3O9:Cr3+near-infrared phosphors were successfully synthesized.Under the excitation of blue light,the Na3ScSi3O9:Cr3+phosphor can produce a broadband nearinfrared emission of 650-1350 nm,the emission peak is located at 898 nm,and the half-peak width is 247 nm.The optimal doping concentration of Cr3+ions in Na3ScSi3O9 and the thermal stability of phosphors were explored.Furthermore,a cationic disordering strategy was employed to achieve tunable emission with peak wavelengths in the range of 850-898 nm through Na/Li substitution.Compared with the Na3ScSi3O9:Cr3+material,when the Li content is 0.5,the overall luminous intensity of the obtained Na2.5Li0.5ScSi3O9:Cr3+material is increased by about 4.2 times,and the thermal stability is also significantly improved.On this basis,a series of Na2.5Li0.5ScSi3O9:Cr3+,Yb3+broadband near-infrared luminescent materials were synthesized through Yb3+ ions and utilizing the efficient energy transfer between Cr3+→Yb3+,and their luminescent properties were studied in detail.Under the excitation of blue light,Na2.5Li0.5ScSi3O9:2%Cr3+,0.5%Yb3+material can produce characteristic emission of Cr3+and Yb3+at the same time,and the FWHM of the emission band is extended to 234 nm,realizing ultra-broadband near-infrared light emission.Meanwhile,at high Yb3+doping concentration(7%),the phosphors can be efficiently excited by blue light and produce short-wave infrared emission at 900-1150 nm.After adding Yb3+,the thermal stability of Na2.5Li0.5ScSi3O9:Cr3+,Yb3+can reach 64%@125℃.Based on NIR ultra-broadband phosphors(Na2.5Li0.5ScSi3O9:2%Cr3+,0.5%Yb3+)and short-wave infrared phosphors(Na2.5Li0.5ScSi3O9:2%Cr3+,7%Yb3+)that can be excited by blue light,two infrared LED lightemitting devices were encapsulated and their light-emitting properties were studied in detail.Finally,a series of night vision monitoring,non-destructive monitoring,biological tissue imaging,information recognition and other applications were carried out with self-made infrared LED,and satisfactory results were achieved,showing the important application prospect of Na2.5Li0.5ScSi3O9:Cr3+,Yb3+ phosphors.This work provides an effective way to optimize the luminescence properties of Cr3+-doped broadband luminescent materials.