Preparation And Optical Properties Of Cr³⁺ Single-Doped And Eu³⁺/Cr³⁺ Co-Doped GdAlO₃ Crimson Long Persistent Luminescent Nanoparticles

Near-infrared long afterglow luminescent nanomaterials are often used as biological imaging nanoprobes due to their high imaging resolution.In addition,magnetic resonance imaging is widely used in medical examinations because it is harmless to the human body and suitable for deep tissue imaging.However,compared with optical imaging,the detection sensitivity of magnetic resonance imaging is lower,which may lead to misdiagnosis.Long afterglow imaging can make up for this shortcoming.The material can keep emitting light for a long time after being irradiated with the excitation light for a period of time,which can be excited before detection and imaging.So it will greatly avoid the background interference caused by the excitation light during biological imaging,which has the advantage of high signal-to-noise ratio.In summary,In order to play a complementary role,that is,to achieve high spatial resolution and high sensitivity imaging results,and obtain more comprehensive and accurate diagnostic information,it is important to prepare new nanoparticles that can be simultaneously used as contrast agents for magnetic resonance imaging and optical probes for near-infrared afterglow optical imaging in biomedical field.In this paper,single-phased GdAlO3:x%Cr3+and GdAlO3:1%Cr3+,y%Eu3+near-infrared persistent luminescent nanoparticles with different doping concentrations were prepared by a self-propagating combustion method.Their microstructure and optical properties were studied by means of X-ray diffraction,scanning electron microscopy,excitation and emission spectra and luminescent kinetics analysis.1.It is found that,for Cr3+single doped samples,Cr3+ions replace the Al3+sites and the average particle size is?202 nm.From excitation spectra of GdAlO3:x%Cr3+samples,it can be found that,the excitation peaks at 240,424 and 583 nm are attributed to the 4A2?4T1(4P),4A2?4T1(4F)and 4A2?4T2(4F)transitions of Cr3+,respectively,and the excitation peaks corresponding to 275 nm and 313 nm originate from the 8S2/7?6Ij and 8S2/7?6P2/7 transitions of Gd3+ions.Meanwhile,four emission peaks appear in the near-infrared range of 650-750 nm upon 583 nm excitation.Among them,the emission peak at 725 nm belongs to the zero phonon line(PZL)and those peaks at 700 and 750 nm can be attributed to the emissions from phonon sidebands(PS)of the 2E?4A2 forbidden transitions,respectively.In the doping concentration range of 0.1%-2.0%,with the increase of chromium ion doping concentration,the intensity of these emission peaks increases first and then decreases,and the optimal concentration is 1%.However,the intensity of the emission peak at 735 nm increases with the increase of Cr3+concentration,which is attributed to the emission from Cr3+-Cr3+pairs.It is found that long afterglow luminescence at 725 nm can be observed for Cr3+single-doped nanoparticles.Among them,the afterglow time of GdAlO3:1%Cr3+nanoparticles is the longest and exceeds 30 s.2.On the basis of the above optimal Cr3+concentration(1%),single-phased Eu3+/Cr3+co-doped GdAlO3 nanoparticles were prepared by the replacement of Gd3+by Eu3+.It is found that several emission peaks dominated by the emission at 614 nm(from the electrical dipole transition from 5D0?7F2 of Eu3+ions)can be observed in the red region under 266 nm excitation(from the absorption of the charge transfer state of Eu3+).In particular,near-infrared emission peak of Cr3+at 725 nm appears under 266 nm excitation due to the presence of the energy transfer from Eu3+to Cr3+.It is found that GdAlO3:1%Cr3+,13%Eu3+sample exhibits the strongest afterglow emission intensity of Cr3+at 725 nm among Cr3+/Eu3+co-doped samples after stopping 275 nm UV light irradiation for 5 minutes.3.Compared to the Cr3+single-doped sample,despite average particle size of Eu3+/Cr3+co-doped GdAlO3 nanoparticles is reduced to?167 nm,its near-infrared afterglow emission intensity is significantly enhanced.By the comparative analyses of the results of emission spectra and luminescence kinetics of single-doped and co-doped samples,it is proved that the existence of a persistent energy transfer from Eu3+to Cr3+leads to the enhanced near-infrared afterglow intensity.Meanwhile,this study provides new strategies for designing new near-infrared long persistent luminescent nanomaterials.