Cr³⁺ Doped Phosphors For NIR/PersL And MRI Dual-function Imaging Markers

Near-infrared Persistent luminescence?NIR-Pers L?material is an attractive and versatile material platform because of its low autofluorescence,strong tissue penetration,low background scattering,high signal-to-noise ratio,and physical and chemical stability.The advantages of high performance can be used for real-time research and applications in the fields of chemistry,biomedicine and others.Especially,the field of biological imaging has become one of the research hotspots.At present,Cr³⁺-doped near-infrared persistent luminescence materials have attracted much attention,but most of research are mainly focused on gallates,and most rely on high-energy ultraviolet light for charging to obtain afterglow.A new study has been reported on galliate materials that can restore afterglow in vivo imaging using a red-near-infrared laser with strong tissue penetration,but require high-energy ultraviolet pre-charge in vitro before in vivo imaging.Red–near–infrared light is inefficient for excitation and charging,which limits its application to in situ and in vivo imaging.In addition,single-mode biological imaging is far from meeting the current medical conditions,such as low optical resolution or low magnetic sensitivity,and multi-mode imaging can achieve complementary purposes.In order to solve the existing problems of Cr³⁺doped near-infrared Persistent luminescence materials,three new types of Cr³⁺doped titanate and stannate systems(Gd₂MgTiO₆?Ga₄SnO₈?Na_0.5Gd_0.5TiO₃)are designed in this paper.Near-infrared Persistent luminescence materials and characterization analysis.?1?Gd₂MgTiO₆:Cr³⁺phosphor with double perovskite structure was synthesized by high-temperature solid-phase method.Due to the energy level transition of Cr³⁺,two sharp peaks centered at 734 and 756 nm?²E?⁴A₂?,and a broadband near-infrared emission?650–950 nm??⁴T₂?⁴A₂?;The amount of doped Cr³⁺with the best fluorescence intensity is x=0.25%and micron-level fluorescence lifetime.The sample is effectively charged in the ultraviolet region.The temperature of peak maximum in TL curves is?110?,and the luminescence can be continuously emitted for more than 30 min with 254 nm of mercury lamp.Due to the inclusion of Gd,the sample also exhibits paramagnetism.Changing the amount of Cr³⁺can regulate the magnetic moment value.With near-infrared Persistent luminescence and paramagnetic properties,it is expected to perform optical-magnetic dual-mode imaging,thereby solving the problem of a single imaging mode.?2?Ga₄SnO₈:Cr³⁺phosphor with tunnel structure was obtained by high-temperature solid-phase reaction.A broadband emission centered at 785 nm?650–950 nm?due to the ⁴T₂?⁴A₂transition of Cr³⁺.After charging with full-spectrum?276–802 nm?light,it is shown that it is effectively charged mainly under UV-visible light excitation,and the temperature of peak maximum in TL curves is?100?,but it can be effectively charged under low-energy red-near infrared light660–740 nm LED light and obtain near infrared Persistent luminescence.The amount of doped Cr³⁺with the best fluorescence intensity,Persistent luminescence intensity and TL intensity is 0.25%,which is close to the quenching concentration of0.32%.It has micron-level fluorescence lifetime and belongs to the two-photon charging mechanism.it can be charging with low-energy red-near infrared light and obtain Near-infrared Persistent luminescence,to solve the problem of relying on high-energy light charging to obtain the Persistent luminescence,and it is expected to realize in-situ charging with deep red–near infrared light,thereby real-time biological in vivo imaging.?3?We synthesized the Na_0.5Gd_0.5TiO₃:Cr³⁺NIR-Pers L material with perovskite structure by high-temperature solid-phase method.The sample exhibited a wide emission band centered at 761 nm under UV-visible excitation.Persistent luminescence can be obtained under full-spectrum?276–802 nm?LED light charging.Thereinto,Cr³⁺cation acts as the recombination center,and the ⁴T₂?⁴A₂transition contributes the efficient NIR-Pers L.The Na_0.5Gd_0.5TiO₃:Cr shows over 100 times stronger NIR-Pers L intensity than the best known Cr³⁺-doped gallates under ultralow-irradiance??2.5?W/mm²?and noncoherent?652 nm light charging.Based on the studies of the charging-irradiance dependent integrated TL intensities and the constructed HRBE schemes,we found an one-photon charging process in Na_0.5Gd_0.5TiO₃:Cr,while those of Cr³⁺-doped gallates through two-photon mechanism.Tissue-penetration verification and in-vivo bioimaging demonstrated the renewed high SNR in-situ imaging potentials with low-irradiance??19?W/mm²?and noncoherent red–NIR source.The one-photon charging NIR-Pers L will contribute the new mechanism to guide the design of the high-tissue-penetration NIR imaging probes with laser-free and ultralow-irradiance red–NIR excitation.Therefore,the problems of in vivo biological imaging relying on high-energy ultraviolet pre-charge in vitro and low-near infrared excitation and charging efficiency are solved.In addition,the sample has paramagnetism,combined with optical properties,can realize optical-magnetic dual-mode imaging.