In recent studies, amorphous silica (SiO2) has been used as a host matrix for rare-earth ions
to prepare luminescent materials that can be used in various light emitting devices. Sol-gel
glasses have the potential to hold up to â¥10% dopants without losing their amorphous
structure. However, before rare earth (RE) - doped sol-gel glasses can be used as luminescent
material, several fluorescence quenching mechanisms must be overcome. There are several
quenching mechanisms which are present in all materials that are more serious in sol-gel
glasses. The first is cross relaxation which involves energy transfer between RE elements; the
others are energy transfer through lattice vibrations and to hydroxyl (OH) groups which are
present due to the use of water as the solvent during the preparation process. A few studies
have demonstrated that the luminescence intensity of rare-earth doped silica can be improved
through incorporation of co-dopants such as Al, TiO2, B and by annealing at high
temperatures (e.g. > 500ºC).
Following their footsteps and in order to make comparisons, we used aluminum as the codopant
in some samples to investigate the effects on luminescence yield for various RE
concentrations. We also investigated the effects of magnesium co-dopant and high
temperature annealing on the luminescence intensity of rare-earth doped silica. In this work,
the highest emission intensity was observed for the sample with a composition of 0.5 mol%
Ce3+. Cerium doped silica glasses had broad blue emission corresponding to the D3/2- FJ
transition at 445 nm but exhibited apparent concentration quenching after higher
concentrations of 0.5 mol% Ce3+. Silica containing Mg2+ or Al3+ ions displayed an increase
in luminescence intensity as the Mg2+ or Al3+ to Ce3+ ratio increases for the range
investigated but significant luminescence enhancement was observed for Mg2+:Ce ratio
greater than 20, while that of Al3+ co-doping had the highest luminescent intensity when the
ratio of Al:Ce is 10:1. This enhanced photoluminescence was assigned to an energy transfer
from the Mg nanoparticles, to result in enhanced emission from Ce3+. The Al3+ or Mg2+ ions
disperses the Ce3+ clusters, enhancing 2F5/2 and 2F7/2 emissions due to increased ion-ion
distances and decreased cross-relation.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07232013-103827 |
| Date | 23 July 2013 |
| Creators | Koao, Lehlohonolo Fortune |
| Contributors | Prof HC Swart, Prof BF Dejene |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07232013-103827/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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