# XEOL and Persistent Luminescence in Eu- and Ti-Doped Lu2O2S Materials

## TL;DR

This paper studies the optical and luminescent properties of Lu2O2S materials doped with Eu, Ti, and Mg, synthesized via a new microwave method.

## Contribution

The first synthesis of these materials via a microwave-assisted solid-state method and detailed analysis of their luminescent and structural properties.

## Key findings

- Microwave synthesis produced phase-pure Lu2O2S and doped variants with confirmed crystal structures.
- XEOL and XANES confirmed matrix absorption at Lu L3-edge enhances luminescence.
- Ti remains in Ti4+ state, indicating no photoredox processes in persistent luminescence.

## Abstract

Rare-earth oxysulfides
(RE2O2S,
RE3+ = Y, La, Gd, Lu) are promising matrices for luminescent
materials
due to their high thermal and chemical stability, cost-effectiveness,
and efficient sensitization of trivalent lanthanide ions, leading
to high luminescent efficiency. These compounds crystallize in a trigonal
structure, belonging to the space group P3̅m1. Lutetium oxysulfide (Lu2O2S) has
been extensively studied as a host material for three-dimensional
plasma display panels, field emission displays, and light-emitting
diodes. Lu2O2S:Eu3+ exhibits red
persistent luminescence, while Lu2O2S:Ti features
a broad orange emission band associated with titanium. The incorporation
of Mg2+ enhances afterglow duration by creating charge
compensation defects and facilitating energy storage in trap levels.
This work investigates the crystalline structure, optical absorption,
and persistent luminescence properties of Lu2O2S and its doped variants: Lu2O2S:Eu3+, Lu2O2S:Ti, and Lu2O2S:Mg2+. Additionally, codoping effects were explored in
Lu2O2S:Eu3+,Ti, Lu2O2S:Eu3+,Mg2+, Lu2O2S:Ti,Mg2+, and Lu2O2S:Eu3+,Ti,Mg2+. The materials were synthesized for the first
time via a rapid and energy-efficient microwave-assisted solid-state
method. Phase purity and crystal structure were analyzed by X-ray
diffraction (XRD) with Rietveld refinement. The incorporation of Eu3+, Ti and Mg2+ was assessed along with resulting
structural modifications. Lu2O2S band gap energy
was obtained with Kubelka–Munk function on the diffuse reflectance
spectroscopy (DRS) data. X-ray Absorption Near Edge Structure (XANES)
and X-ray Excited Optical Luminescence (XEOL) measurements confirmed
that absorption by the matrix at the Lu L3-edge effectively
induces luminescence, playing a positive role in the emission mechanism.
EPR spectra of Lu2O2S:Ti and Lu2O2S:Eu3+,Ti materials suggested that, even though
Ti3+ might be present, photoredox processes are absent
in the persistent luminescence mechanism and that Ti remains in the
Ti4+ state. The observed visible-light emissions upon UV
and X-ray excitation, along with the high energy storage capacity,
highlight the potential of these materials for applications in dosimetry,
bioimaging, and optoelectronic devices.