Design And Research On The New Type NIR Persistent Phosphors

Phosphors with long afterglow also known as persistent luminescence（Pers L）,can continuously emit light from several minutes to hours after ceasing the external irradiation source.As a special kind of photoluminescence materials,Pers L phosphors have been widely used in many important fields,such as security sign,decoration and optical memory.In recent years,the development of near-infrared（NIR）Pers L phosphors has aroused great research interest owing to their remarkable advantages in the areas of bio-imaging and detection of radiation.Especially,the NIR Pers L phosphors with light emission located in“biological transmission window”have the characteristics of long afterglow lifetime and intense tissue penetration ability.Compared to traditional fluorescent probe materials such as organic dyes,fluorescent proteins as well as quantum dots,using NIR Pers L phosphors as optical imaging labels for biological imaging could realize the separation of excitation and emission light,which completely avoids the tissue autofluorescence,phototoxicity,and effectively improves the signal-to-noise ratio and resolution of imaging system.Therefore,the research on NIR Pers L phosphors is of great significance.Based on the current limitations of NIR Pers L phosphors,this paper provides a series of new NIR Pers L phosphors from different perspectives（host,activator as well as methods）,and systematically characterizes and analyzes their afterglow properties.The main research results include the following three parts:（1）A novel non-gallate NIR Pers L phosphor Ca Zn Ge₂O₆:Cr was successfully fabricated by a high-temperature solid-state reaction,Under 254 nm UV light excitation,the as-synthesized phosphor shows a broad NIR photoluminescence（PL）,afterglow emission band in the range of 650-900 nm,and the afterglow decay time exceeds 600 s.The optimal synthesis conditions and Cr³⁺doping concentration of this phosphor were determined.The test of PL,Pers L spectra confirm that broad NIR emission band of the phosphor Ca Zn Ge₂O₆:Cr is attributed to the ⁴T₂→⁴A₂transition of Cr³⁺.Combining the results of afterglow decay curve and thermoluminescence（TL）spectra,the NIR fluorescence and long afterglow mechanism of phosphor Ca Zn Ge₂O₆:Cr are further discussed systematically.（2）In view of the fact that NIR Pers L phosphors emitting in“biological transmission windowⅡ”are still relatively rare.In this paper,Bi³⁺and Pr³⁺co-doped NIR Pers L phosphors Li YGe O₄:Bi,Pr was successfully synthesized via a high-temperature solid-state method through reasonable construction of energy transfer（ET）channel.Under the excitation of 254 nm UV light,the co-doped phosphor Li YGe O₄:Bi,Pr exhibits excellent PL,Pers L emission bands peaks at 364 nm and 1072 nm,respectively.The PL,Pers L,TL spectra and afterglow decay curve measurement of the as-synthesized phosphor were carried out.Results indicate that the emission band centered at 364 nm and 1072 nm are around 1072 nm is attributed to the ET process from Bi³⁺to Pr³⁺.A possible mechanism of this NIR Pers L phosphor Li YGe O₄:Bi,Pr is also discussed in detail.（3）Combined with the up-conversion（UC）anti-Stokes properties of rare earth ions,a triple doped NIR Pers L phosphor Zn_1.3Ga_1.4Sn_0.3O₄:Yb,Er,Cr was designed and successfully prepared by a high-temperature solid-state reaction.Under the irradiation of980 nm laser,this phosphor shows efficient UC emission properties,and the UC spectra mainly consists of green（524 and 547 nm）,red（659 nm）as well as NIR（694 nm）In addition,the phosphor Zn_1.3Ga_1.4Sn_0.3O₄:Yb,Er,Cr also displays intense NIR Pers L emission upon the excitation of UV or visible light.Owing to the ET process of Yb³⁺/Er³⁺to Cr³⁺,the NIR Pers L is realized by 980 nm NIR light activation.A possible mechanism of NIR UC and Per L emission is also proposed according to the test results of PL,Pers L and TL characteristics.