Synthesis of NaYF4:Yb–Tm thin film with strong NIR photon up-conversion photoluminescence using electro-deposition method

Abstract

Rare earth-doped fluorides with strong up-conversion (UC) luminescence have attracted growing attention due to their potential applications in photonics and biological areas. However, current techniques to process these fluorides into thin films have not been sufficiently developed. Here, we report for the first time the preparation of NaYF₄ thin film doped with Yb³⁺, and Tm³⁺ by electro-deposition and subsequent annealing. The as-deposited thin film was characterized by X-ray diffraction, scanning electron microscopy, thermogravimetry, differential thermal analysis and photoluminescence. Under excitation by a near infrared laser diode at 980 nm, the transparent NaYF₄:Yb–Tm thin film exhibits bright visible upconversion luminescence from Tm³⁺ as a result of energy transfer from Yb³⁺. The results demonstrate that the electro-deposition process provides facile access to UC fluoride thin films which may have applications in photovoltaic devices.