Nanocrystals Based Ionizing Radiation Sensor (Scintillator)
Scintillation is a luminescence induced by ionizing radiation. Scintillators are scintillating materials which can emit ultraviolet or visible photons when excited with ionizing radiations. Scintillators have played a major role in the development of modern physics, acting as particle and radiation detectors. Nowadays, scintillators are used in a more broad range of application fields, including but not limited to:
1. High-energy physics and particle detector (e.g. alpha particle detector);
2. Spectrometry of lower energy gamma-quanta (e.g. Mossbauer Spectrometer);
3. Applications in medical imaging (X-ray radiology, Computed Tomography, Positron Emission Tomography, etc.);
4. Safety systems (e.g. X-ray luggage examiner); and
5. Space applications (e.g. Global Large Area Telescope --- a high energy observatory for gamma�Cray from out space)
Specifications of ideal scintillators include high light output, high stability, fast decay time (no afterglow), high density, large production volume, and good energy-dependent linearity. However, material meeting all these specifications is not yet available. Thus, current scintillators are tailored to have certain desired qualities from the above list prioritized over others based on the requirements of the user.
Figure 1. Optical image of scintillation emission out of cadmium-free quantum dots in toluene solution (quantum dot concentration: 2 mg/mL, radiation source: x-ray generated at voltage 80 kV and current 250 µA on Tungsten target).
In Mesolight, we develop scintillating quantum dot (StNCs) based materials and products. These quantum dots (Qdot) are nanometer scale particles, composed of thousands of atoms. Size wise, they are larger than an atom but smaller than a virus. Developed from proprietary technology in Mesolight, these Qdot are sensitive to X-ray radiation and emit visible yellow photons. Figure 1 shows an optical image of the scintillation Qdot, with yellow emission peaked at 585 nm, well suited for detection by silicon photodetector.
Figure 2. Transparent st-Qdot/polymer composite thin film.
These StNCs present a number of special features that make them an ideal fit for applications in scintillators. Test results show StNCs emit higher light output than numerous single crystal and plastic scintillators. Shown in Figure 1, a solution of StNCs has strong emission at a low concentration of w.t. 0.2%. Traditional single crystal scintillators are bulky in size. It is difficult to grow them into desirable shapes, especially thin films and curved shapes. In contrary, StNCs are tiny nanoparticles ideal for solution processing or modifying through polymers to form composite materials. They are well tunable in shape and size in both solid and liquid forms. Visible transparent StNCs/polymer composite thin film with StNCs load up to w.t. 74% has been prepared by Mesolight (Figure 2).
StNCs features cadmium-free composition, a unique advantage over cadmium or mercury based Qdots, which are in doubt for future uses due to their environmental and toxicity concerns. In addition, StNCs presents high stability as they are neither hygroscopic nor sensitive to ambient operation conditions. Also, they have medium lifetime in the scale of 1 µs, suitable for most scintillators.
Figure 3. Scintillating quantum dots (st-Qdot) powder 1.5 g in plastic tube: (left) room light yellow powder, (right) bright orange scintillation emission under X-ray irradiation.
With the innovation in developing novel scintillating StNCs, Mesolight is changing the future of scintillators. StNCs based next generation scintillators will feature high contrast, high resolution, tunable detector structure, and cost efficient qualities.