Optically based radiation detectors in various fields of science still suffer from low resolution, sensitivity and efficiency that restrict their overall performance. Quantum dots (QD) are well-suited for such detectors due to their unique optical properties. CdTe QDs show fast luminescence decay times, high conversion efficiencies, and have band gaps strongly dependent on the particle radius. Since QD particle sizes are well below the wavelengths of their emissions, they remain optically transparent when incorporated in both polymer and sol-gel based silica glass due to negligible optical scattering. In addition, as these composite materials can greatly improve the mechanical robustness of alpha-particle detectors, conventionally known to have delicate components, CdTe QDs show high promise for radiation sensing applications. These properties are especially advantageous for alpha-particle and potentially neutron detection. In this work, CdTe QD-based glass or polymer matrix nanocomposites were synthesized for use as alpha-particle detection scintillators.. The fast photo-response and decay times provide excellent time resolution. The radiation responses of such nanocomposites in polymer or glass matrices were investigated.
The use of light emitting nanoparticles in polymer and glass matrices was studied for the detection of radiation. These
nanocomposite scintillators were produced by various approaches including quantum dot/polymer, fluoride
nanophosphor/epoxy and halide nanophosphor containing glass-ceramic composites. The synthesis and characterization
of these nanoparticles as well as their incorporation into composites is discussed. Further, the application of these
composites for radiation detection and spectroscopy is described.
Nuclear radiation detection is continuously becoming more important for today's society. Conventional scintillator
based gamma-ray detectors use single crystal materials such as NaI:Tl, LaBr<sub>3</sub>:Ce, which provide excellent radiation
detection properties, but suffer from their environment-related fluctuation, high cost and size limitation. The
incorporation of nanophosphors or quantum dots (QD) into a transparent host matrix has been studied recently as a cost-saving
alternative that may solve the scalability and stability problems while still providing considerable optical
performance. In this work, a new glass based detecting material with promising gamma-ray detection performance is
reported. Transparent alumino-silicate glasses containing cerium-doped gadolinium halide nanocrystals were prepared by
a melt-quench method followed by annealing to form nanocrystal precipitates. Samples were cast and polished for
optical and radiation characterization. The preliminary results indicated a similar gamma-ray detection efficiency
compared to a conventional NaI:Tl detector and a gamma-ray peak resolution of ~27% at 662 KeV from some of these
samples. By controlling elemental composition and ratio of the in-situ precipitated nanoparticles, radiation detection
performance is expected to be improved.
Intense visible blue to red emissions were obtained from SiN<sub>x</sub> thin films prepared by plasma enhanced chemical vapor deposition (PECVD) using SiH<sub>4</sub> and NH<sub>3</sub> as the source gases. A continuous blue shift of the photoluminescence (PL) peak from 660nm to 440nm was observed by increasing the NH<sub>3</sub> flow rate from 20 to 150sccm, while the flow rate of N<sub>2</sub> diluted 2% SiH<sub>4</sub> was fixed at 650sccm. This controllable PL was attributed to the quantum confinement effect of Si quantum dots (QDs) which were formed during the deposition process and embedded in the SiN<sub>x</sub> films. White photoluminescence with multiple emission peaks was achieved for potential solid state lighting applications from multi-layered SiN<sub>x</sub> films by changing the SiH<sub>4</sub>/NH<sub>3</sub> ratio during the deposition process. This was attributed to a combination of Si quantum dots with different sizes within the different layers. Surface texturing of the thin film samples was conducted by potassium hydroxide (0.56%) etching the (100) Si substrate for 3~40 min at 80°C before deposition. The reflectivity of the etched samples decreased with increasing etch time due to increased surface roughness. The extraction efficiency of light emission from the textured SiN<sub>x</sub> thin films was significantly improved, owing to a depression of the internal reflection and interference effects. In addition, the elimination of the multiple emission peaks by surface texturing significantly affected the color coordinates of the output spectrum.
Silicon quantum dot (QD) based luminescent structures can emit throughout the visible region by controlling their size and/or the host matrix. Consequently, multiple sized Si QDs embedded in thin films could be used to produce efficient white light sources, when integrated with a blue/UV LED, and film structures designed for high light extraction. In this paper, we report strong red photoluminescence from Si QDs embedded in films prepared by thermal evaporation of SiO in vacuum or an O<sub>2</sub> atmosphere. The SiO<sub>x</sub> film composition (1.0< x <1.9) was controlled by varying the deposition rate and the oxygen flow rate in the chamber. After annealing at 1100°C, silicon nanocrystals of 20nm to 2nm in size were formed in films with different stroichiometry, as indicated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization. Red photoluminescence was observed from films with Si QDs smaller than ~5nm, and attributed to confined carrier radiative recombination in the Si QDs. The emission peak shifted from 840nm to 745nm with increasing O<sub>2</sub> flow rate due to a decrease in the size of the Si QDs.