Sol–Gel Synthesis of Translucent and Persistent Luminescent SiO2@ SrAl2O4 Eu, Dy, B Materials (original) (raw)
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Silica glasses doped with Eu 3þ were prepared by the sol-gel method. The effects of the synthetic procedure on optical properties of the europium heavily doped glasses have been investigated. The fluorescence characteristics of Eu 3þ have been measured for several thermal stages of the sol-gel process. In particular, we have studied aggregation of the Eu ions leading to creation of nanocrystallites during the thermal treatment of silica glasses. The size of the nanocrystalites and their structure have been determined by means of high-resolution transmission electron microscopy and X-ray diffraction. The influence of the OH À groups on the luminescence lifetimes of Eu 3þ has been studied. A broad luminescence band in the blue region has been observed for the silica glasses possessing silanol (Si-OH) groups. Its intensity decreases with the increasing temperature of sintering for the samples treated in the presence of NH 4 Cl. In the case of those heated at high temperatures, doubly doped with Eu and Al silica glasses, a blue emission assigned to the Eu 2þ ions has been observed. Its intensity increases with the Al 3þ ions concentration. Ó
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Rare-earth silicate glasses have been obtained by a sol-gel method starting with the rare earth carbonates of Pr, Dy and Er and TEOS (tetraethoxysilane). Expressed in the form xLn*O,(l x)SiO,, the glasses have compositions in the range x = 0.009 to 0.052, which corresponds to 0.9 to 5.2 mol'% or up to 23 wt% rare earth oxide as determined by electron microprobe. The glasses were produced by densification at 800 ' C. Infrared and visible spectra and magnetic susceptibilities are reported.
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Production of luminescent glasses by traditional methods can be expensive and the final products can absorb impurities owing to the high temperatures involved which reduce the luminescent efficiency. The sol-gel method provides a lower temperature alternative to synthesising these glasses, giving improved homogeneity and greater control over the composition and conditions. The incorporation of rare-earth activators into various silica glass matrices using sol-gel techniques is described and selected results are given. The paper covers general applications of these products, giving a brief but valuable insight into this vast subject area.
Improved photoluminescence properties of sol-gel derived Er3+ doped silica films
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Silica films (amorphous and crystalline) doped with erbium were fabricated on silica glass substrate and characterized. The inorganic-organic hybrid sol-gel method was used to prepare the films and the Na codoping induced the crystallization of silica film. Photoluminescence (PL) measurements revealed that the Er3+ ions can be excited from the ground state through an energy transfer process mediated by active defective sites in SiO2 film matrix. The annealing temperature and atmospheres have large effects on the local environment of Er3+ and the 1.54 μm PL intensity can be improved significantly by suitable heating treatments. We could correlate Er3+ sensitization effect due to the presence of carbon related species in the films. The PL intensity at nonresonant (476.5 nm) condition can be made as intense as the resonant (488 nm) one, for particular annealing conditions. Noticeable changes in PL emission intensities have not been observed whether the matrix silica film is amorphous or crystalline in nature; however, the defect-related luminescence is almost vanished in case of crystalline silica films.
Structure and site selective luminescence of sol–gel derived Eu:Sr2SiO4
Journal of Luminescence, 2012
Strontium silicate (Sr 2 SiO 4) samples doped with varying Eu 3 þ content were prepared via sol-gel route and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS) and photoluminescence (PL) techniques. The synthesis temperature could be brought down to 600 1C for formation of a singe phase sample. The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Eu 3 þ ions was evaluated based on which the quenching mechanism was verified to be a multipole-multipole interaction. Based on the timeresolved emission data (TRES), it was inferred that, two different types of Eu 3 þ ions were present in the matrix. The first type was a long lived species (t¼ 4.7 ms) present at 10-coordinated 'Sr'sites and the other was a short lived species (t¼ 1.2 ms) present at the 9-coordinated 'Sr'sites which gets selectively excited at 296 nm. Judd-Ofelt (J-O) intensity parameters for both the species were evaluated. The trend observed for the two species in the J-O parameters, O 2 and O 4 were different confirming their existence in two different environments. The color coordinates of the system were evaluated and plotted on a CIE index diagram. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor.