Power-dependent upconversion luminescence properties of self-sensitized ErWO phosphor.

A Yb free self-sensitized ErWO phosphor has been synthesized via a solid-state reaction method. The phosphor material, ErWO, has a monoclinic crystal structure with space group P2/c (13). The deconvoluted high-resolution X-ray photoelectron spectra of all the core elements in the ErWO phosphor material were explored. The highly resolved absorption peaks in the ultra-violet, visible and near-infra-red (NIR) regions of the diffuse reflectance spectrum were due to the Stark-splitting of the 4f energy levels of the Er ions. Under 980 nm NIR laser excitation, the ErWO phosphor showed an intense up-converted red emission at 677 nm due to the F→I transitions of the Er ions. The cross-relaxation and resonance energy transfer process involved in the key intermediate F and F levels of the Er and their role in generating red emissions were investigated. The laser pump power versus upconversion intensity plot showed a slope with an n value <1 and the possible reasons behind this behavior were investigated. The photoluminescence properties of the ErWO phosphor in the visible and NIR region were further analyzed. The potential application of the phosphor as a marker in latent fingerprint detection was also evaluated.