Correlation of EPR and Photoluminescence Analysis for Crystalline Defects in Eu3+/Yb3+-Doped Lutetium Silicate Sol–Gel Powders

Crystalline defects such as oxygen vacancies have been studied little by electron paramagnetic resonance (EPR) spectroscopy for silicate-based luminescent materials. In this study, lutetium oxyorthosilicate powders were prepared by the sol–gel method, using TEOS (silicon source) and rare earth salts as precursors. The cross-linking agent, Glymo, contributed silicon atoms to the precursor solution in all systems. The addition of Glymo to Lu2SiO5, Lu2SiO5:Eu and Lu2SiO5:Eu/Yb influenced the morphology and chemical structure of the powders, leading to Lu2Si2O7 formation. The crystalline defects in the lutetium silicate systems were investigated by EPR spectroscopy, and several defects related to oxygen were identified, as well as impurities from the precursors. Photoluminescence emission spectra revealed Eu3+ transitions between 5D0 → 7F0, 5D0 → 7F1 and 5D0 → 7F2 under 258 nm excitation, in addition to oxygen vacancy emissions between 500 and 550 nm. Oxygen vacancies were identified and confirmed by correlating EPR and photoluminescence studies.