RESUMO
Ordered mesoporous highly luminescent SiO2 particles have been synthesized by spray pyrolysis from solutions containing tetraethylorthosilicate (TEOS) and either cetyltrimethylammonium bromide (CTAB) or the block copolymer Pluronic F-68 as structure-directing agents. Rhodamine B (RhB)-containing samples were prepared by using a simple wet impregnation method followed by the growing of a second silica shell in order to prevent leaching of the dye. The obtained materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder x-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis) and photoluminescence (PL). Powders with polydisperse spherical grains were obtained displaying an ordered hexagonal array of mesochannels. Luminescence results reveal that RhB molecules have been successfully encapsulated into the channels of mesoporous particles as monomeric species and that a well-defined silica coating hindered dye leaching.
RESUMO
An investigation by optical spectroscopy of the Eu3+ and Er3+ active ions in the crystallized fluorozirconate matrix LaZr2F11 is presented. The 5D1-->7F0-5 emission lines of Eu3+ are used to extract the 7F0-5 energy scheme and the observed extinctions permit the deduction of irreducible representations (IRREPS) associated with corresponding sub-levels in the D2 symmetry. The crystal field analysis was carried out on a 387 x 387 basis set, comprising the 7F, 5D(1,2,3) 5F(1,2), 5G(1,2,3) and 3P(1,2,3,4,5,6) terms of the Eu3+ 4f6 configuration. The deviation and rms are 6.8 and 7.9 cm(-1), respectively for 38 levels and ten parameters. The experimental crystal field parameters are in good agreement with the ab-initio ones. Moreover, the relative intensities of the 5D0-->7F2,3,4 emissions are well reproduced by an 'ab-initio' calculation, except for three lines. The Er3+ ions introduced in LaZr2F11, microcrystals also lie in an unique crystallographic site. A total of 31 energy levels were recorded and the crystal field analysis led to 6.6 and 7.8 cm(-1) for the deviation and rms, respectively, for nine variable parameters taken into account. The experimental CF parameters for Er3+ and Eu3+ are very similar, which seems to show that the host lattice contracts around the smaller Er3+ ion. The informations given by both Eu3+ and Er3+ optical probes in LaZr2F11 are very consistent with the structure previously determined for the isotypic PrZr2F11 fluoride.
