Preparation And Optical Properties Of Near Infrared Emitting Mn⁴⁺ Doped Lu₂O₃ Phosphors

Nowadays,near-infrared luminescent materials have attracted attention because of their wide applications in many fields such as anti-counterfeiting identification,laser communication and medical diagnosis.In particular,the near-infrared emission within the first biological transmission window?650-950 nm?can effectively reduce the autofluorescence background from biological tissues and exhibit higher signal-to-noise ratio than luminescent materials with ultraviolet and visible emissions,showing potential applications in medical imaging.Owing to the strong emission in the near-infrared region,the doping of transition metal ions(such as Cr³⁺and Mn⁴⁺)has become a hot topic in this research field.Recently,researchers have prepared some Mn⁴⁺doped near-infrared long-lasting luminescent materials.However,the limited host materials and unrevealed persistent luminescence mechanism related to Mn⁴⁺doped materials compared with that with Cr³⁺ions.There are urgent needs to find matrix materials with simple and specific structure,acquire novel Mn⁴⁺doped near-infrared long afterglow materials,and unravel the relationship between the luminescence properties and the specificity of the host material.This research is helpful for further understanding of the near-infrared long-lasting luminescence mechanism and develop a new type of near-infrared long afterglow material.It has practical significance for the development of near-infrared biomedical applications.In this dissertation,novel near infrared?NIR?emitting Lu₂O_3:x%Mn⁴⁺?x=0.05,0.10,0.20,0.30,0.50?phosphors were prepared by a high temperature solid-state method.The effects of the Mn⁴⁺doping concentration,sintering time and synthesis temperature on the microstructure,luminescent properties and afterglow performances of Lu₂O₃:Mn⁴⁺phosphors were investigated.Upon 252 nm excitation,the observed NIR emissions peaked at 695 and 712 nm originate from ²E?⁴A₂ and ⁴T₂?⁴A₂ transitions,respectively.The strongest luminescent intensity can be obtained when the Mn⁴⁺doping concentration is⁰.1%.The thermal luminescence curves indicate that suitable traps exist in Lu₂O₃:Mn⁴⁺phosphor related to long afterglow luminescence.The luminescence properties and afterglow performances of Lu₂O₃:0.1%Mn⁴⁺phosphors were improved by changing the sintering time?2 h,4 h,5 h,6 h?.It was found that the optimized luminescence and afterglow performances were obtained when the sintering time was 5 h.In addition,different sintering temperature?1300°C,1400°C,1500°C?were explored to prepare Lu₂O₃:0.1%Mn⁴⁺phosphor.Based on the analyses of the microstructure,luminescence and afterglow properties,phosphors annealed at 1400°C in air for 5 hours exhibit optimized properties.The fluorescence decay curve suggests that Mn⁴⁺ions occupy S₆ and C₂ sites in Lu₂O₃ host.The NIR emission with the longer lifetime originates from Mn⁴⁺ions occupying S₆ sites,and the one with shorter lifetime comes from the Mn⁴⁺ions occupying C₂ sites.The results suggest that near infrared emitting Mn⁴⁺doped Lu₂O₃ phosphors has potential applications in bioimaging.