Preparation And Luminescence Properties Of Cr³⁺ Activated Deep Red/Near Infrared Phosphors

Semiconductor lighting technology has significant advantages of high efficiency,energy saving and environmental protection,which has set off a revolution in lighting and display industry.Fluorescent conversion LED（pc-LED）is the main type of semiconductor lighting devices,in which the phosphor powder plays a key role in determining the light efficiency,spectral structure and life of the device.Semiconductor lighting industry segments continue to expand,light source research and lighting applications are no longer limited to meet the needs of visual efficacy,"non-visual lighting"gradually become a new focus of research and development.The research of LED phosphor is also expanding to deep red and even near infrared.Deep red light can well match the P_FR absorption peak of green plants and promote plant growth and development.Near infrared light has important applications in food detection,biological imaging,spectral testing,machine vision and other fields.In this paper,the transition metal ion Cr³⁺and rare earth ion Yb³⁺were introduced into different oxide substrates as luminescence centers by the traditional high temperature solid-state reaction method.Gd Al O₃:Cr³⁺deep red phosphor and Li In Si₂O₆:Cr³⁺,Yb³⁺and Ga₂O₃:Cr³⁺,Yb³⁺near infrared phosphor were synthesized.The phase structure,luminescence properties and the performance of packaged pc-LED devices were studied systematically.The main results are as follows:Gd Al O₃:Cr³⁺dark red phosphor was successfully prepared by high temperature solid state method,and its luminescence performance was greatly improved by introducing NH₄F flux.The luminescence system can be excited by the blue light of 350～480nm,and matches well with the blue LED chip.Gd Al O₃:Cr³⁺occupies the octahedral position of Al³⁺in the Cr³⁺phosphor,located in a strong crystal field environment,so it presents narrow band emission from ²E to ⁴A₂.The sharp emission peaks are located at 727nm and 735nm respectively,and the half-peak width is less than 10nm,which is well matched with the PFR absorption band of plants.Gd Al O₃:Cr³⁺phosphor internal quantum efficiency up to 93.2%,150℃can still maintain 98%of room temperature luminescence intensity,excellent luminous efficiency and thermal stability,is very suitable for plant lighting applications.Li In Si₂O₆ phosphors co-doped with Cr³⁺and Yb³⁺were successfully prepared by high temperature solid state method.In Li In Si₂O₆:Cr³⁺,Yb³⁺,there exists Cr³⁺→Yb³⁺resonant nonradiative energy transfer,and its mode of action is dipole-dipole interaction.The co-doping of Yb³⁺can significantly enhance the emission in the 950-1100nm band.The optimized system Li In Si₂O₆:0.06Cr³⁺,0.003YB³⁺phosphors can be excited by blue light effectively,the emission coverage is 700-1150nm,and the half-width is about 230nm.The luminescence efficiency and thermal stability are good,and the internal quantum efficiency is about 76.7%,which can keep80%of the luminescence intensity at 150℃.The near-infrared pc-LED device made of its package has a near-infrared output power of 36m W at 100m A current and a photoelectric conversion efficiency of 11.8%.Li In Si₂O₆:Cr³⁺,Yb³⁺phosphors show excellent near-infrared luminescence properties and have a good application prospect.Ga₂O₃:Cr³⁺,Yb³⁺phosphors can be excited by blue light effectively,and the co-luminescence of Cr³⁺and Yb³⁺can be realized through Cr³⁺→Yb³⁺,but there is emission loss in 850～950nm band.Doping Al³⁺makes Cr³⁺emission blue shift,Cr³⁺→Yb³⁺energy transfer weakened,Yb³⁺emission intensity decreased;Doping In³⁺makes Cr³⁺emission redshift,Cr³⁺→Yb³⁺energy transfer enhanced,and Yb³⁺emission enhanced.Ga_1.6In_0.4O₃:Cr³⁺,Yb³⁺can produce continuous spectral emission covering 700-1100nm,with a half-width of 220nm and a quantum efficiency of 91%.The output power of the packaged NIR pc-LED device is 32m W at a current of 100m A,and the photoelectric conversion efficiency is about 11%.It shows good comprehensive luminescence performance.