Structural and optical properties of Eu3+/Gd3+ ions in silica xerogels and powders obtained by sol–gel method

Abstract

The xerogels and sol–gel powders with different quantitative composition have been studied based on excitation and emission measurements as well as luminescence decay analysis. The structure of prepared silica sol–gel materials was examined using FT-IR spectroscopy technique. The photoluminescence spectra of Eu3+ ions were registered upon two different excitation wavelengths related to direct excitation of Eu3+ ions (λexc = 393 nm) and indirect excitation through energy transfer process from Gd3+ to Eu3+ (λexc = 273 nm). Upon direct excitation of Eu3+ (7F0 → 5L6 transition) the characteristic emission bands assigned to the 5D0 → 7FJ(0–4) electronic transitions were observed. Also, it was found that enhanced luminescence of Eu3+ is a result of change the excitation parameter through energy transfer phenomenon (8S7/2 → 6IJ transition of Gd3+) and occurred in both xerogels and powder samples. In this way, a UV photon absorbed by Gd3+ is converted into visible light emitted by Eu3+ ions. Obtained results clearly indicated that high concentration of Gd3+ ions in powders led to particularly strong enhance the emission in red spectral range and allowed for more than 12-times prolongation of luminescence lifetime for the 5D0 excited state of Eu3+ compared to silica xerogel samples. The values of energy transfer efficiency were also estimated based on luminescence decay times of the 6P7/2 state of Gd3+ ions.