Fig. 17From: Recent progress in the development of upconversion nanomaterials in bioimaging and disease treatmentCopyright 2019. Elsevier. Reproduced with permission.)Synthesis of NaYF4:Yb3+,Tm3+@TiO2 and mechanism of aPDT under NIR irradiation. Upon NIR irradiation, the UCNP nucleus converts NIR light into ultraviolet (UV) light and the UV light in turn excites TiO2 to generate active oxygen, which eventually causes oxidative damage against the microorganisms. (Back to article page