Power-dependent upconversion luminescence properties of self-sensitized Er2WO6 phosphor.

A Yb3+ free self-sensitized Er2WO6 phosphor has been synthesized via a solid-state reaction method. The phosphor material, Er2WO6, 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 Er2WO6 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 Er3+ ions. Under 980 nm NIR laser excitation, the Er2WO6 phosphor showed an intense up-converted red emission at 677 nm due to the 4F9/2 → 4I15/2 transitions of the Er3+ ions. The cross-relaxation and resonance energy transfer process involved in the key intermediate 4F3/2 and 4F5/2 levels of the Er3+ 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 Er2WO6 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.