Particle size effects of nano- and polycrystalline metal tungstate MWO4 (M = Ca, Pb, Cd) scintillators were examined
through a comparison of commercially available powders and solution precipitation prepared nanoscaled materials. The
scintillation behaviors of nanoparticles and commercial powders were examined with ion beam induced luminescence
(IBIL), photoluminescence (PL), and cathodoluminescence (CL) spectroscopy techniques. For commercial microns
sized MWO4 powders, spectral emission differences between CL and PL were only observed for Cd and Pb tungstates
when compared to reported single crystals. The IBIL wavelength emissions also differed from the commercial MWO4
CL and PL data and were red shifted by 28 and 14 nm for CaWO4 and CdWO4; respectively, while PbWO4 had no
significant change. IBIL analysis on CaWO4 nanoparticles produced a 40 nm blue shift from the commercial powder
emission. These preliminary results suggest that both size and cation Z may affect the emission properties of the MWO4
scintillators.
Scintillating nanomaterials are being investigated as replacements for fragile, difficult to synthesize single crystal
radiation detectors, but greater insight into their structural stability when exposed to extreme environments is needed to
determine long-term performance. An initial study using high-Z cadmium tungstate (CdWO4) nanorods and an in-situ
ion irradiation transmission electron microscope (I3TEM) was performed to determine the feasibility of these extreme
environment experiments. The I3TEM presents a unique capability that permits the real time characterization of
nanostructures exposed to various types of ion irradiation. In this work, we investigated the structural evolution of
CdWO4 nanorods exposed to 50 nA of 3 MeV copper (3+) ions. During the first several minutes of exposure, the
nanorods underwent significant structural evolution. This appears to occur in two steps where the nanorods are first
segmented into smaller sections followed by the sintering of adjacent particles into larger nanostructures. An additional
study combined in-situ ion irradiation with electron tomography to record tilt series after each irradiation dose; which
were then processed into 3D reconstructions to show radiation damage to the material over time. Analyses to understand
the mechanisms and structure-property relationships involved are ongoing.
Using a many-body embedded ion method potential for La-Br system, molecular dynamics simulations
have been performed to study dislocations in the UCl3 type of LaBr3 crystal including identification of
dislocation line energy, core structure, migration mechanism, and mobility. We found that dislocations with
the < 0001 > Burgers vector can move under shear stresses, but they retain perfect dislocations during the
motion rather than dissociated partials as commonly seen in metal systems. Unlike the < 0001 > edge
dislocations whose mobility increases with temperature, the < 0001 > screw dislocations may become
sessile at high temperatures due to thermally activated dissociation of the core. Dislocations with the
<1120 > Burgers vector were found to be sessile due to non-planar dissociation at the core. Because the
< 0001> dislocations can only slip on the {1 1 00 } prism plane and often only the edge dislocations are
operative, the stresses created during any thermal mechanical processes cannot be effectively relieved by
the plastic deformation mechanism. Considering that LaBr3 tend to cleave along the {1 1 00 } prism plane,
the simulations shed some lights on why this material is so brittle and how large LaBr3 crystals tend to
fracture during growth.
Anhydrous cerium bromide (CeBr3) and cerium doped lanthanum bromide (Ce+3-LaBr3) were obtained by the
dehydration of hydrates synthesized by a direct acidification process. The dehydration process involves heating in
vacuum through three phase changes - hydrate, amorphous, and crystalline LaBr3. Incomplete removal of the
bound water leads to the formation of oxybromides and the partial reduction of the lanthanum at high temperatures.
It was found that upon the completion of dehydration (< 200 °C) a complete solid solution can be formed between
LaBr3 and CeBr3. These two compounds form a simple binary phase diagram. Challenges associated with the
dehydration process are discussed.
Embedded waveguides and integrated optical devices are fabricated from a computer-aided design file by scanning the focus spot in amorphous silica, using femtosecond laser pulses (800 nm, <125 fs, at 1 kHz). The effect of laser processing conditions on the optical properties of direct-written waveguides and an unusual laser-induced birefringence in an optically isotropic glass are reported. Several integrated optical devices, including Y coupler, directional coupler, and Mach-Zehnder interferometer, are made to demonstrate the simplicity and flexibility of this technique in comparison to the conventional waveguide fabrication processes.
Embedded waveguides and their optical properties in bulk silicate glasses fabricated by femtosecond (fs) laser pulses (800 nm, <120 fs, at 1 kHz) are reported. Experimental results show that there is a narrow operating window for our system to produce low loss waveguides. An angular dependence of light transmission measured between two crossed polarizers on these laser-modified regions suggests that these regions possess an optical birefrigent property.
Furthermore, the optical axes of laser-induced birefringence can be controlled by the polarization direction of the fs laser. Permanent optical birefringence induced by the fs laser pulses can be produced in amorphous silica, and borosilicate glass. Raman spectroscopy of the modified glass shows a densification and reconstruction of silica network in the glass. Results show that the amount of laser-induced birefringence depends on pulse energy level and the number of accumulated pulses. Mechanisms that contribute to the observed laser induced birefringence behavior are discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.