Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application / von Julia Selling [original]

UNIVERSITÄT PADERBORN

FAKULTÄT FÜR NATURWISSENSCHAFTEN – DEPARTMENT PHYSIK

Barium Halide Nanocrystals

in Fluorozirconate based Glass Ceramics

for Scintillation Application

Dissertation zur Erlangung des akademischen Grades

Doktors der Naturwissenschaften

vorgelegt dem

Fachbereich Physik

der Fakultät für Naturwissenschaften

Universität Paderborn

von

DIPL. PHYS. JULIA SELLING

Paderborn, 2007

Abstract

Europium (Eu)-activated barium halide nanocrystals in fluorozirconate based glass ceram-

ics represent a promising class of x-ray scintillators. The scintillation in these glass ceramics

is mainly caused by the emission of divalent Eu incorporated in hexagonal BaCl2nanocrys-

tals which are formed in the glass matrix upon appropriate annealing. Experiments with

cerium (Ce)-activated fluorozironate glass ceramics showed that Ce is an interesting al-

ternative. In order to get a better understanding of the scintillation mechanism in Eu-

or Ce-activated barium halide nanocrystals, an investigation of the processes in the cor-

responding bulk material is essential. The objective of this thesis is the investigation of

undoped, Eu-, and Ce-doped barium halides by x-ray excited luminescence (XL), pulse

height, and scintillation decay spectra. That will help to figure out which of these crystals

has the most promising scintillation properties and would be the best nanoparticles for the

glass ceramics. Furthermore, alternative dopants like samarium (Sm) and manganese (Mn)

were also investigated.

Besides the above-mentioned optical investigation electron paramagnetic resonance (EPR)

and Mössbauer measurements were carried out in order to complete the picture of Eu-

doped barium halides. The EPR data of Eu-doped BaI2is anticipated to yield more infor-

mation about the crystal field and crystal structure that will help to understand the charge

carrier process during the scintillation process. The main focus of the Mössbauer investi-

gations was set on the Eu-doped fluorochlorozirconate glass ceramics. The results of this

investigation should help to improve the glass ceramics. The Eu2+/Eu3+ratio in the glass

ceramics should be determined and optimize favor of the Eu2+. We also want to distinguish

between Eu2+in the glass matrix and Eu2+in the nanocrystals. For a better understand-

ing of Mössbauer spectroscopy on Eu also measurements on Eu in a CaF2host lattice were

carried out.

iii

In physics, you don’t have to go around making trouble for yourself

- nature does it for you.

Frank Wilczek 1

1Nobel prize-winning American theoretical physicist. Along with H. David Politzer and David Gross, he

was awarded the 2004 Nobel Prize in Physics "for the discovery of asymptotic freedom in the theory of the

strong interaction".

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