Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The large band gap (approximately 11.5-12.1 eV) and high transmission of calcium fluoride
(CaF2) crystal in the ultraviolet (UV) and vacuum ultraviolet (VUV) region makes it
an important material for optics for laser applications in UV. However, CaF2 degrades
during long exposure to UV irradiation due to defect generation. The formation of selftrapped
excitons (STE) is considered the first step in defect generation. In this project
the possibility of observing STE states in CaF2 using a narrow bandwidth tunable VUV
laser source is investigated. This is the first spectroscopy study of an alkaline earth fluoride
using VUV tunable laser radiation instead of a fixed wavelength laser. The use of a VUV
tunable laser source has potential for determining the energies of the STE states, which are
unknown. Our main objective is addressed by developing techniques to measure absorption
spectra of pure and doped CaF2 samples, using a VUV scanning monochromator and a
tunable VUV laser, and by doing a literature study. The results obtained with the scanning
monochromator show absorption features in 126-180 nm range of all our samples. These
vary for different samples and correlate with information from the supplier on the samples’
fluorescence spectra. Total absorption of the VUV light by CaF2 in the 115-126 nm range is
observed. With the narrow bandwidth tunable laser light, absorption spectra were obtained
in the range of 143-146.7 nm of all our CaF2 samples. No significance peaks which can be
related to the STE states in CaF2 were observed in the VUV laser absorption spectra, but
the results are valuable to improve the technique. The conclusion is that either a different
spectral range or fluorescence detection can be investigated in future. / AFRIKAANSE OPSOMMING: Die groot bandgaping (ongeveer 11.5-12.1 eV) en hoë transmissie van kalsiumfluoried
(CaF2) kristal in die ultraviolet (UV) en die vakuum ultraviolet (VUV) gebied maak dit
’n belangrike materiaal vir optika vir laser toepassings in die UV. CaF2 degradeer egter
gedurende langdurige blootstelling aan UV lig as gevolg van die generering van defekte.
Die vorming van ’n elektron-holte paar wat deur die kristalstuktuur gestabiliseer word teen
rekombinasie (self-trapped excitons, afgekort STE) word beskou as die eerste stap in defek
generering. In hierdie projek word die moontlikheid ondersoek om STE toestande in CaF2
waar te neem deur die gebruik van ’n afstembare VUV laserbron met emissie in ’n smal
spektrale band. Dit is die eerste spektroskopiese studie van ’n aardalkali-fluoried deur die
gebruik van afstembare VUV laserlig in plaas van ’n vaste golflengte laser. Die gebruik
van ’n afstembare VUV laserbron het potensiaal vir die bepaling van die energieë van die
STE teostande, wat onbekend is. Ons hoofdoel word aangespreek deur die ontwikkeling
van tegnieke vir die meet van absorpsie spektra van suiwer en gedoteerde CaF2 monsters
met behulp van ’n VUV skanderende monochromator en ’n afstembare VUV laser, en
deur ’n literatuurstudie. Die resultate wat behaal is met die skanderende monochromator
toon die absorpsieprofiele van al ons monsters in die 126-180 nm spektrale gebied. Die
absopsieprofiele varieer vir die verskillende monsters en korreleer met die inligting van die
verskaffer oor die fluoressensie spektra van die monsters. Totale absorpsie van die VUV lig
deur CaF2 in die 115-126 nm gebied is waargeneem. Met die smalband afstembare laserlig
is absorpsie spektra in die 143-146.7 nm gebied vir al ons CaF2 monsters verkry. Geen
beduidende pieke wat verband hou met die STE toestande in CaF2 is waargeneem in die
VUV laser absorpsie spektra nie, maar die resultate is waardevol vir die verbetering van
die tegniek. Die gevolgtrekking is dat of ’n ander spektraalgebied of fluoressensiedeteksie
in die toekoms ondersoek kan word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95804 |
| Date | 12 1900 |
| Creators | Matindi, Tresor |
| Contributors | Steenkamp, Christine M., Rohwer, Erich G., Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xi, 104 p. : col. ill. |
| Rights | Stellenbosch University |
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