Influences Of Si Doping On Afterglow Properties Of Zn₂Ga_2.98Ge_0.75-xSi_xO₈:Cr_0.02³⁺ Nanoparicles For Potential Bioimaging

In recent years,near infrared?NIR?persistent luminescent nanomaterials has potential applications in bioimaging because of their glow emission wavelength falling within the first biological window?650-1000 nm?.In this case,real-time images can be obtained without external excitation and it can effectively avoid the effect of autofluorescence.Thus,this strategy is more convenient and superior to that based on the upconversion luminescence.Among them,chromium doped zinc gallogermanate(ZGGO:Cr³⁺)NIR persistent luminescence nanoparticles?PLNPs?with an afterglow emission wavelength of⁷00 nm have achieved the afterglow imaging in vivo due to their excellent afterglow performance?the afterglow time exceeding 15 hours?.The high-quality bioimaging shows that the ZGGO:Cr³⁺nanoparticles has potential applications in the biomedical field,such as tumor diagnosis and therapy.To meet the application requirements of ZGGO:Cr³⁺PLNPs,it is essential to make ZGGO:Cr³⁺nanoparticles have good afterglow properties and dispersibility in solutions?such as aqueous solution and blood?.At present,the commonly used method is to coat a thin layer of SiO₂ on the surface of ZGGO:Cr³⁺bare nanoparticles and the improved dispersibility of these nanoparticles dispersed in solution can be realized by forming a silicon hydroxyl group on the surface of the SiO₂ thin layer.However,the above preparation process is cumbersome and laborious.Therefore,it is still a key issue on how to prepare ZGGO:Cr³⁺bare nanoparticles with excellent afterglow performance and good stable dispersibility in the solutions.In this dissertation,Si doped zinc gallogermanate nanoparticles with different concentrations?x=0,0.025,0.05,0.075,0.10,0.125,0.15?,namely Zn₂Ga_2.98Ge_0.75-xSi_xO₈:Cr³⁺_0.02(ZGGSO:Cr³⁺),were prepared by a hydrothermal method and following a post-vacuum heat treatment.It is found that the size distribution of all nanoparticles was in the range of 44-58 nm.The emission and absorption spectra show that all samples have a narrow-band and broadband superimposed emission around 700 nm,which are attributed to the transitions of Cr³⁺ion from the ²E and ⁴T₂ states to the ⁴A₂ state.Through the spectral analysis and calculation,it is found that Cr³⁺ions occupy the sites in a medium-intensity crystal field environment,and as the Si doping concentration increases,the crystal field strength gradually becomes weaker.From the afterglow decay and thermoluminescence curves and the luminescence kinetics analysis of the sample?x=0.025?,it is found that the strong afterglow performance?the longest afterglow time?can obtained.This result can be explained by two reasons.On one hand,Si doping leads to the change in the trap distribution of the sample and the increased number of anti-defects.On the other hand,Si doping effectively increases the energy transfer rate from the deep trap to Cr³⁺ions.For ZGGSO:Cr³⁺nanoparticles with different concentrations?x=0,0.025 and 0.10?,the photoluminescence intensity of these nanoparticles dispersed in water decreases with increasing measurement time.It is found that,for the sample with x=0.10 sample,the luminescent intensity decay rate was lower compared to the other samples.When the measurement time reaches 960 min,the normalized luminescent intensities of the three solutions containing ZGGSO:Cr³⁺nanoparticles were 30%,37%and 60%,respectively.In addition,the surface potential measurement shows that as the Si doping concentration increases from 0 to 0.10,the surface potential value increases from 5 mV to³7 mV.Our results suggested that Si doping can effectively improve the dispersion performance of ZGGSO:Cr³⁺bare nanoparticles in aqueous solution and ZGGSO:Cr³⁺nanoparticles have potential applications in bioimaging.