Insights into Microstructural Features Governing Ce³⁺ Luminescence Efficiency in Sol−Gel Silica Glasses

Abstract

The radioluminescence (RL) properties of Ce-doped silica glasses prepared by sol−gel method were investigated as a function of the dopant amount in a wide range of concentrations (Ce:Si molar ratios from 1 × 10-5 to 5 × 10-2). The effects of xerogel densification temperature and of a postdensification thermal treatment were also considered. In order to understand the microstructural features governing Ce3+ luminescence efficiency, optical absorption measurements in the ultraviolet, visible, and infrared regions and time-resolved photoluminescence experiments were performed. The complex dependence of RL intensity upon rare-earth (RE) concentration and thermal treatment was attributed to the role of OH vibrations as nonradiative recombination channels, as well as to the formation of RE aggregates in the silica matrix. Specifically, the segregation of CeO2 nanoparticles, in which Ce4+ does not supply any radiative emission, has been revealed by infrared absorption measurements, in agreement with previous Raman, transmission electron microscopy, and X-ray diffraction data. Moreover, an optical absorption band, centered at 2.4 eV and whose intensity increases with the square of cerium concentration, was observed and tentatively assigned to an intervalence electron-transfer transition involving Ce3+−Ce4+ dimers. Postdensification thermal treatments markedly reduce the intensity of this band and increase RL intensity. The relationship between the 2.4 eV band and the RL properties will be outlined. In particular, the increase in RL intensity will be discussed, mainly as a consequence of microscopic modifications leading to an improvement of the charge-transfer efficiency toward emitting centers.

Significance of host׳s intrinsic absorption band tailing on Ce3+ luminescence quantum yield in borate glass

“…Moreover, the weak absorption due to defect centers shows a hump at about 4-5 eV and spans over a wide spectral region. The defect absorption arises due to the presence of various kinds of point defects in glass such as the wrong bonds, dangling bonds, non-bridging oxygen ions, vacancies, impurities, etc, forming localized states in the band-gap region [12][13][14][15][16]. These Gaussian-like localized distribution exhibit weak absorption bands below the Urbach tail, which together gives rise to an extended band tailing to the fundamental absorption of host glass.…”

Optical properties and radiation hardness of Pr-doped sol-gel silica: Influence of fiber drawing process

“…However, at concentrations above 1 mol%, the formation of RE-rich clusters was detected. This phenomenon was found to affect the scintillation efficiency as well as the glass homogeneity [1][2][3].…”

“…The glass synthesis can be performed by using high purity precursors, reducing the level of unwanted impurities [1]. This latter factor is an essential feature for the radiation hardness of such materials.…”

Ce-doped SiO 2 optical fibers for remote radiation sensing and measurement

“…In this paper, we propose a novel type of glass composite fiber dosimeter based on the RL emission of a small portion of glass fiber doped with Cerium. Previous investigations already demonstrated the interesting RL properties of these composite fibers [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Moreover, with the aim to better separate the Cherenkov emission from the scintillating signal [36,37] an alternative Eu doped fiber was produced, tested and compared with Ce-doped ones.…”