Influences Of Sn⁴⁺ Doping On The Microstructure And Near Infrared Persistent Luminescence Of ZGGO:Cr³⁺ Nanoparticles

Nowadays,the study on disease diagnosis and therapy using the techniques related to in vivo bioimaging has become a research hotspot in the field of biomedical science.Among them,the strategy that realized biolabeling and bioimaging using near infrared?NIR?persistent luminescence nanoparticles has been considered as one of the most promising methods.Especially,because this method does not need external excitation during the bioimaging and the effect of background autofluorescence on the bioimaging can be avoided,the bioimaging quality can be improved.Recently,the bioimaging by using chrome-doped zinc gallogermanate(ZGGO:Cr³⁺)nanoparticles with strong NIR persistent luminescence has been realized.However,it is essential to further increase the afterglow intensity and time for realizing high quality bioimaging.In particular,for ZGGO:Cr³⁺ nanoparticles,the key issues on how the variations in the crystal field strength around Cr3-ions and deep trap depth related to the anti-site defects influence the energy transfer process between the Cr³⁺ ions and the deep traps remain unclear.To resolve the aforementioned problem,it will be helpful for designing and acquiring novel NIR persistent luminescence nanoparticles for in vivo bioimaging.In this dissertation,Zn2Ga2.98Ge0.75-xSnxO8:Cr³⁺0.02(ZGGSO:Cr³⁺)?x=0,0.015,0.030,0.063,0.125 and 0.250?NIR persistent luminescence nanoparticles with various Sn substitution concentrations were prepared through a hydrothermal method in combination with a subsequent vacuum annealing.For these nanoparticles,it can be found that the average particle size are in the range of 30-45 nm.The EDX analysis showed the existence of Sn element.The refined XRD patterns,Raman spectra and XPS analyses indicated that Sn⁴⁺ ions substituted for Ge⁴⁺ ions and the lattice constant and the Zn-O and Ga-O and Cr-O bond lengths increased with increasing Sn⁴⁺ substitution concentrations.Emission spectra showed that there existed two emission peaks at 697 and 712 nm,respectively,which originated from the transitions from the 2E and 4T2 states to the 4A2 state,respectively.For the sample with higher Sn substitution concentration,it also can be found the emission intensity peaked at 712 nm is higher than that peaked at 697 nm compared to the sample without Sn⁴⁺,suggesting the weakened crystal field around Cr³⁺ ions after Sn substitution because of the increased Cr-O bond length.From the afterglow decay curves,it can be found that the sample with x=0.015 exhibits the longest afterglow time,indicating more anti-site defects(Zn'_Ga-Ga_zn⁰)are generated after Sn4-substitution.Meanwhile,since Sn substitution can tune the variation in the crystal field strength around Cr³⁺ and modulate the energy distance between the 4T2 level of Cr3-and the deep trap,the energy transfer process between the 4T2 level of Cr3-and the deep trap can be controlled and the enhanced persistent luminescence can be acquired.By using the pellet pressed by the ZGGSO:Cr³⁺ powders as an image target,a clear red pellet image can be obtained after 254 nm or X-ray excitation through 5 mm pork skin covered on the surface of the pellet.It can be found that the red image will disappear with the decay time of several minutes after stopping the external excitation,but the red pellet image can be retraced using 808 nm laser stimulation at any time.