Tunable Dual Visible and Near-Infrared Persistent Luminescence in Doped Zinc Gallogermanate Nanoparticles for Simultaneous Photosensitization and Bioimaging

Zinc gallogermanate nanoparticles have been synthesized by a sol-gel process with adjustment of Zn2+, Ga3+ and Ge4+ ratios and subsequent sintering at 1000 oC. The resulting X-ray diffractograms can be simulated by variation of the ratios α, β, γ in the standard cards of αZnGa2O4-βZn2GeO4-γGeO2. Similarly, the FT-IR and Raman vibrational spectra are sums of the spectra of the individual components. The major difference in our synthesis of the ratio α:β:γ = 1:1:1 compound, ZGGO, from previous studies is the contribution of Zn2GeO4 in the rhombohedral lattice system and not the cubic phase. Photoluminescence and electron spin resonance spectra supply sensitive analyses of our samples and show the presence of zinc and oxygen vacancies, with the latter playing an important role in emission. In particular, a tunable visible emission band is discovered which can be deconvoluted into several Gaussian components. The lowest energy band, at ~520 nm, gives the strongest persistent luminescence and it is tunable by ...