Study On Synthesis And Luminescence Properties Of Broadband Near Infrared/Red Phosphors Doped With Nickel Or Manganese Ions

The technological and cost advantages resulting from the rapid development of white LEDs has afforded pc-NIR-LEDs with the advantages of low cost,simple structure,high efficiency,and long lifetime expectancy.The strategy of using ultraviolet(UV)or blue light chips to excite phosphors and enable continuous broadband NIR emission is an ideal candidate for new broadband NIR light.Therefore,it has become extremely urgent to develop broadband NIR phosphors to realize the application of pc-NIR-LED light sources.Aiming at the problem of broadening the bandwidth of the NIR wavelength and band,the representative transition metal ions Ni were selected as the luminescence centers.In view of the current shortage of high-efficiency red phosphors for warm white LEDs,research on high-performance red phosphors plays an important role in high-quality white light illumination.Mn⁴⁺activated phosphors usually exhibit intense red/deep-red emission excitated in the UV and blue-green regions.The controllable adjustment of the emission peak position and bandwidth of the phosphor can be achieved by rationally adjusting the phase,crystal field intensity and ion species of the phosphor.The research is carried out using the route:material design,structural performance characterization,luminescence performance characterization and application demonstration.The research content of this thesis mainly focuses on the following aspects:(1)Ni²⁺-doped Y₃Al_5-xGax O₁₂phosphor were prepared by high temperature solid state reaction method.The broadband SWIR(typically in the wavelength range of 900-1700 nm)phosphors with an emission band of 1000-1600 nm and a half-peak width of 250 nm were obtained.Via tuning phase structure,doping concentration and host composition,the variation rule of broadband NIR luminescence was explored.The prepared phosphor has dual functions including near-infrared persistent luminescence and photochromism.By adjusting the Ga/Al ratio to change the"band gap"of the host material,the SWIR persistent luminescence and photochromic properties can be regulated.An energy level schematic diagram of electron excitation,capture and release by"trap"is established to discuss the SWIR persistent luminescence and photochromism mechanisms in detail.(2)Aiming at the problem of structural distortion caused by the substitution of trivalent Al/Ga sites by divalent Ni²⁺-doped Y₃Al₂Ga₃O₁₂(YAGG)host,resulting in weak luminescence intensity and low thermal stability.In order to improve the luminescence intensity and thermal quenching performance of the Ni²⁺-doped garnet phosphor,a strategy for synergistic enhancement is proposed:on the one hand,by adding co-doping ions as"charge compensators",the effect of co-substitution of different tetravalent ions on its structure and luminescence properties is studied,and it is found that the SWIR luminescence intensity and bandwidth can be effectively increased.On the other hand,increasing the flux to improve the crystal quality.The two routes were used together to enhance the SWIR luminescence intensity and thermal stability.The effects of different lattice ion substitutions and different co-solvent additions on the SWIR luminescence properties of Ni²⁺-doped YAGG were systematically studied.It is found that the co-doping ions of Ni²⁺and Zr⁴⁺can effectively improve the SWIR luminescence,and the addition of co-solvent H₃BO₃ has a best effect.Compared with Ni²⁺single-doped YAGG phosphors,the NIR luminescence intensity of YAGG-Ni-Zr-H₃BO₃phosphors enhanced by 20 times.The coordination number and substitution site of Ni²⁺and Ni²⁺,Zr⁴⁺co-doped Al/Ga³⁺were studied in detail using density functional theory(DFT)calculations and experiments.The prepared optimized phosphors were encapsulated in NUV LED chips to obtain pc-SWIR LEDs,and the application of broadband pc-SWIR-LED light sources was demonstrated.(3)In order to further improve the luminescence intensity and thermal quenching performance of the Ni²⁺-doped garnet phosphor,Y_3-xLu_xAl_5-yGay O₁₂:Ni²⁺phosphors were designed and synthesized.By gradually replacing Y ions with Lu ions,the crystal field environment and the degree of structural distortion are improved to improve the near-infrared luminescence intensity.At the same time,through the synergistic effect of charge compensators(Si,Zr,Ge,Sn and Ti)and flux(H₃BO₃),the SWIR luminescence intensity and thermal stability are greatly improved.The as-prepared optimized phosphors were encapsulated in NUV LED chips to obtain pc-SWIR-LEDs,and the application prospects in the field of biological imaging were demonstrated.