Er3+ Sensitized Photon Upconversion Nanocrystals

Lanthanide doped upconversion nanocrystals, showing bright future in diverse fields, are typically excited by approximate to 700-1000 nm light when Nd3+ and Yb3+ are used as sensitizers. Thus far, extending the excitation range of upconversion nanocrystals is still a formidable challenge. Herein, a new type of upconversion nanocrystals is reported, using Er3+ ions as sensitizers, which can be excited by 1532 nm light located in the second near-infrared biological window. Through Er3+ sensitization, upconversion emission from a series of activators, including Nd3+, Ho3+, Eu3+, and Tm3+, is obtained and can be modulated by Yb3+ codoping. In addition, Er3+ sensitized photon upconversion of Ho3+ and Tm3+ can be further enhanced by shell coating. It is found that Er3+ sensitized upconversion processes are mainly dependent on the energy transfer between Er3+ ions and activators. Considering the demonstration of anticounterfeiting by using this newly designed nanocrystal, it is anticipated that these results can bring more opportunities to upconversion nanomaterials in other aspects, ranging from lasing to super resolution imaging.