The improved size distribution and NIR luminescence of ZGGO:Cr3+nanoparticles induced by Y3+doping

Zn2Ga2.98-xYxCr0.02Ge0.75O8 (ZGGO:Cr0.02,Yx) persistent luminescent nanoparticles (PLNPs) with different con-centrations were synthesized by a hydrothermal method combined with a vacuum heat treatment. With increasing Y3+ concentration from 0 to 0.05, the average size reduces from 53 to 28 nm and the particle shape changes from irregular to nearly spherical due to Y3+ doping leading to the suppressed growth rate of nano-crystals via surface charge modification. On the basis of spectral analyses and the first-principles calculation, the near infrared (NIR) emission peaks at 703 and 743 nm originate from the 4T2 & RARR;4A2 transition of Cr3+ occupying octahedral Ga3+ sites and the 4A2 & RARR;4T1 transition of Cr3+ occupying tetrahedral Ga3+ sites, respectively. Meanwhile, it is found that Y3+ ions are more likely to occupy tetrahedral Ga3+ sites and it leads to not only the creation of more anti-site defect pairs and the enhanced afterglow intensity but also the increased rigidity and the improved dispersibility of PLNPs in different simulated body fluids induced by complete surface modification (i. e. SiO2 coating). The above results indicate that ZGGO: Cr0.02,Y0.03@SiO2 PLNPs have potential applications in bioimaging.