Silica-Coated Ga(III)-Doped ZnO: Yb3+, Tm3+ Upconversion Nanoparticles for High-Resolution in Vivo Bioimaging using Near-Infrared to Near-Infrared Upconversion Emission.

Photon avalanche has attracted much attention due to the unique nonlinear luminescence dynamics and high-efficiency upconversion luminescence properties. In this paper, we present a simple but effective method to prepare Yb/Tm/GZO@SiO2 (GZO = gallium-doped zinc oxide). Low-threshold photon-avalanche luminescence was obtained below the milliwatts (2.5 mW) in Yb/Tm/GZO@SiO2 core/shell nanoparticles. Compared with Yb/Tm/GZO nanoparitlces, near-infrared (NIR) upconversion luminescence intensity of Yb/Tm/GZO@SiO2 was enhanced ∼12 times. Furthermore, Yb/Tm/GZO@SiO2 acted as luminescence probe, which realized the red fluorescence imaging of myocardial tissue. With injection of 6 mg/kg Yb/Tm/GZO@SiO2, the red NIR fluorescence imaging of heart tissue became brighter. The experimental results of histological assessments of representative organs indicated that there was low toxicity of Yb/Tm/GZO@SiO2 in vivo. This study proved that Yb/Tm/GZO@SiO2 posed a promising potential for bioimaging applications.