Enhancement Of Near-infrared Afterglow By Persistent Energy Transfer From Green To Near-infrared Light

The long persistent luminescence materials are excited by external light sources which are visible light,ultraviolet light and X-ray,etc.Moreover,the long persistent luminescence materials can absorb external energy and be stored in the trap,and they can emit light continuously after the excitation.Due to their unique properties,they are widely used in lighting,emergency instructions and other aspects.They are also applied in the filed of optical imaging of biological tissues in recent years.However,there is a noteworthy mismatch between the vectors and the technologies.But the near-infrared persistent luminescence materials are the best choice of the new probes owing to their deep tissue penetration?emission range in the region of biologically transparent window?,high signal-to-noise ratio?weak light disturbance?,and permitting late time-gated imaging?no continuous irradiation is required for testing?.However,only fewer persistent phosphors in near-infrared region are involved,comparing with the excellent afterglow properties of green and blue persistent luminescent materials,the afterglow of near-infrared persistent luminescent materials is urgent to be improved.Therefore,it is profoundly significance to prepare a series of new near-infrared persistent luminescent materials,which have better afterglow properties.This paper proposed a persistent energy transfer enhancement strategy,firstly SrAl₂O₄:Eu²⁺,Dy³⁺,LiGa₅O₈:Cr³⁺,Mg₂TiO₄:Mn⁴⁺and ZnAl₂O₄:Cr³⁺is synthesized by high temperature solid-state method,and the properties of the composites with different weight ratios were characterizated by emission spectra,decay curves,afterglow emission spectra and TL curves.Afterglow properties and energy transfer mechanism were tested too.The research results in the dissertation can be summarized as follows:1.Green phosphor SrAl₂O₄:Eu²⁺,Dy³⁺and red phosphor LiGa₅O₈:Cr³⁺were synthesized by high temperature solid-state method and then mixed them with different weight ratios.It was showed that the emission spectrum was composed of two bands.One is at 524 nm of SrAl₂O₄:Eu²⁺,Dy³⁺,another is at 718 nm of LiGa₅O₈:Cr³⁺.Through the decay curves of composites,it was found that the afterglow decay speed of the emission at 718 nm of composites were slower than pure LiGa₅O₈:Cr³⁺,which was a substantial proof for the persistent energy transfer from SrAl₂O₄:Eu²⁺,Dy³⁺to LiGa₅O₈:Cr³⁺.In the meantime,the afterglow spectra can prove that the energy transfer efficiency of composites with different weight ratios were different,when the ratio was 1:1,the efficiency was highest.In addition,the TL peaks belongs to SrAl₂O₄:Eu²⁺,Dy³⁺were recorded in the TL curve,by monitoring at 718nm,this was another important evidence.The results proved that energy can transfer from SrAl₂O₄:Eu²⁺,Dy³⁺to LiGa₅O₈:Cr³⁺,and increased the near-infrared afterglow of LiGa₅O₈:Cr³⁺.2.Green phosphor SrAl₂O₄:Eu²⁺,Dy³⁺and red phosphor Mg₂TiO₄:Mn⁴⁺were synthesized by high temperature solid-state method and then mixed them with different weight ratios.It was showed that the emission spectrum was composed of two bands.One is at 524 nm of SrAl₂O₄:Eu²⁺,Dy³⁺,another is at 658 nm of Mg₂TiO₄:Mn⁴⁺.Through the decay curves of composites,it was found that the the emission at 658 nm of composites,showed an obvious afterglow decay process,while pure Mg₂TiO₄:Mn⁴⁺didn't show up,this was a substantial proof for the persistent energy transfer from SrAl₂O₄:Eu²⁺,Dy³⁺to Mg₂TiO₄:Mn⁴⁺.In the meantime,the afterglow spectra can prove that the energy transfer efficiency of composites with different weight ratios were different,when the ratio was 1:2,the efficiency was highest.In addition,the TL peaks belongs to SrAl₂O₄:Eu²⁺,Dy³⁺were recorded in the TL curve,by monitoring at 658 nm,this was another important evidence.The results showed that it successfully achieve the afterglow emission of Mg₂TiO₄:Mn⁴⁺in the composites.3.Green phosphor SrAl₂O₄:Eu²⁺,Dy³⁺and red phosphor ZnAl₂O₄:Cr³⁺were synthesized by high temperature solid-state method,and then mixed with the raw materials of SnF₂-SnO-P₂O₅.The mixture was ground in a agate mortar and then sintered.In the meantime,just mixed SrAl₂O₄:Eu²⁺,Dy³⁺and ZnAl₂O₄:Cr³⁺with various ratios.Through the decay curves of composites,it was found that the emission at 697 nm of composites,showed an obvious afterglow decay process,while the pure ZnAl₂O₄:Cr³⁺,did't show up.This was a substantial proof for the persistent energy transfer from SrAl₂O₄:Eu²⁺,Dy³⁺to ZnAl₂O₄:Cr³⁺.And the energy transfer efficiency of composites with different weight ratios were different.At last,the TL peaks belongs to SrAl₂O₄:Eu²⁺,Dy³⁺were recorded in the TL curve,by monitoring at 697nm,this was another important evidence.It also achieved the afterglow emission of ZnAl₂O₄:Cr³⁺in composites.Comparing with two composites,the energy transfer efficiency from SrAl₂O₄:Eu²⁺,Dy³⁺to ZnAl₂O₄:Cr³⁺didn't increase in composites of SnF₂-SnO-P₂O₅ and two materials.