Rare-Earth Doped, Low Hydroxyl Organically Modified Silicates
- PDF / 342,069 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 61 Downloads / 200 Views
SBecause of their near room temperature processing, gels have emerged as attractive matrices for miscellaneous optically active entities such as laser dyes, photochromes, pigments, etc. [1, 2, 3]. However, pure inorganic gels are still unsuitable hosts for trivalent rare-earth ions. Sol-gel derived matrices usually contain large amounts of hydroxyl groups, the presence of which is detrimental to rare-earth luminescence. Indeed, hydroxyl quenching, with concentration quenching have been reported as major causes for the absence of luminescence in rare-earth doped gels [4, 5]. Therefore, it would be desirable to design a sol-gel derived matrix with little or no hydroxyl groups. Various other approaches have been explored to allow rare-earth fluorescence in gels. They include the modification of the immediate environment of the rare-earth [6], or the use of mixed siloxanes [7]. In this paper, a different approach is explored: the fabrication of low hydroxyl, organicinorganic monolithic matrices by a non-hydrolytic sol-gel process. The preparation of the gel is described, as well as some characterization of the matrix. The low-hydroxyl content of pure gels is confirmed by FTIR, 1H NMR and 2 9 Si NMR. Finally, the low-hydroxyl content of the gels is further ascertained by Er 3 +luminescence. EXPERIMENTAL Several low-hydroxyl gel matrices were fabricated by reacting tertiary butyl alcohol (Aldrich Chemicals, 99.5%) with different silicon halides: methyltrichlorosilane (Aldrich Chemical, 97%), methyldichlorosilane (Aldrich Chemicals, 97%) or silicontetrachloride, (Aldrich Chemical, 97%) or mixtures of the above. Tertiary butanol was added dropwise to the stirred silicon halide solution. All chemical reactions were carried out in a Schlenck line. After reaction, the solution were placed in glass vials or coated onto silicon substrates. Erbium-doped gels were fabricated by the addition of anhydrous ErI3 (0.1-0.5 wt%) into the solution prior to gelation. All samples were kept in a nitrogen-filled glove box during gelation and drying. A synthesis flow chart is shown in Figure 1. Gels were examined by thermogravimetric and differential thermal analyses (Perkin Elmer) in air. FTIR spectra of films on silicon substrates were recorded for low-hydroxyl and triethoxyvinylsilane (TEVS)-based conventional gels used for reference of a trifunctional precursor. Liquid 1H NMR and 29 Si NMR spectra were obtained prior to gelation. Real density of the gels was measured by autopycnometry ( Model 1320, Micromeritics). UV/Visible absorption spectra 803 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
were recorded on a Hewlett Packard Spectrophotometer model HP 8452. The luminescence of Er3 + was measured under 488 nm excitation with an argon laser. • _t-BuOH
I
[Mix3-5sS
Figure 1. Flow chart for the fabrication of low-
ud n
hydroxyl ormosils.
SMix 1/2
Anhydrous
Low-hydroxyl, erbium-doped ormosils RESULTS AND DISCUSSION The reaction of tertiary butyl alcohol with silicon halides has been previously described [8].
Data Loading...
