Custom Scintillation Films
RMD pioneered microcolumnar film technology to produce structured CsI:Tl scintillators based on research and development in the early nineties. Today RMD manufactures structured CsI:Tl scintillators deposited on various substrates ranging in size up to 50 x 50cm and in thickness from tens of microns to over a millimeter. Our current capabilities include the production of custom scintillation films tailored to provide high spatial resolution, high detection efficiency, and enhanced brightness for various applications in digital X-ray imaging.
RMD has become a leader in applying this technology to numerous other inorganic scintillators, including binary and ternary compounds, oxide scintillators, and semiconductor scintillators designed for high-efficiency, high-resolution detection and imaging of X-rays and neutrons. RMD also has the expertise to grow materials that are highly hygroscopic. Unlike powder screens, microcolumnar scintillators channel the light towards the detector with minimal lateral spread, which greatly reduces the conventional need for the tradeoff between efficiency and spatial resolution.
In addition to growing in structured form, RMD tailors the performance of our scintillators through:
- Bandgap engineering to minimize afterglow through co-doping the scintillator
- Using alternative dopants to modify spectral emission
- Modifying growth techniques to achieve thick structures with enhanced brightness and transparency
- Tailoring scintillator host composition for enhanced response to a certain type of radiation and/or to alter its scintillation properties
- Using known scintillators with extraordinary performance to achieve ultra-fast response and/or high brightness
RMD also manufactures powdered scintillators. HSS-1 is our high-speed custom scintillator film designed for fast framing applications and can be produced in desired large sizes and the mass thickness. Other powdered scintillators including the Gd2O2S and LiF/ZnS, as well as custom compositions.
RMD has developed vapor-grown microcolumnar CsI:Tl, which has become the standard for diagnostic digital radiography. Microcolumnar film scintillator materials channel and conserve scintillation light within densely packaged, highly uniform microcolumns. The microcolumns are parallel, needle-like structures controllable in diameter from 250 nm to 10 μm. They number into the millions per square centimeter yielding very high resolution X-ray imaging performance. Films are typically 10 to 700 μm thick, however structures up to 3 mm in thickness are routinely synthesized. Physical sizes may vary from under 1 cm2 to over 48 x 48 cm2 in area, and may be fabricated to any desired shape.
Total internal reflection of the scintillation light within microcolumns yields high spatial resolution, enhanced contrast resolution and near-maximum light yield, without the spread and loss of light inherent in single-crystal amorphous scintillators.
High frame-rate X-ray imaging is a valuable tool for nondestructive testing, ballistic impact studies, in-flight projectile imaging, studies of exploding ordnances, and investigation of other high-speed phenomena.
Due to the short exposures needed to avoid motion-blur, high frame rate imaging is inherently light-starved. This imposes stringent requirements on the performance of the individual system components. The key component in the imaging system is the bright scintillation screen that converts X-rays to visible light images. RMD has developed special High Speed Scintillator, “HSS” custom scintillation film screens that provide a very bright emission coupled with a fast decay time, making it possible to image up to 500,000 fps without image blur. We can manufacture HSS in large-areas up to 20”×40”, and in thicknesses up to 200 mg/cm2 for high-energy X-ray imaging (up to 300 kVp).
RMD’s HSS screens have been demonstrated with projectile imaging at a frame rate of 100,000 fps. The figure on the left shows a single frame of a projectile that was imaged as it traveled at a speed of 3 km/s (6,710 mph). The 36”x36” HSS screen on the left was lens-coupled to an Ultra-17 camera from DRS Technologies.
Lutetium(III) Oxide (Lu2O3:Eu) Scintillation Films
The Lu2O3:Eu scintillator was developed as a joint RMD/ALEM effort, first as a Transparent Optical Ceramic (TOC) and more recently as a deposited film. Lu2O3:Eu has excellent material properties including high density (9.5 g/cm3, highest among known scintillators) and high effective atomic number (Zeff=63). With a light yield of 48,000 photons/MeV and a peak emission in the red at 610 nm, it has excellent potential for X-ray imaging over a range from a few KeV to several MeV.
Lu2O3:Eu scintillation films can be deposited in either columnar format or amorphous crystalline format depending on the application requirements. Films up to 55 µm can be grown for increased stopping power, while the columns provide enhanced spatial resolution.
LNI is a microcolumnar scintillation film used in high-efficiency neutron detection and imaging. LNI films have a 45%, concentration of 95% enriched 6Li which allows for high-efficiency neutron detection. At the same time, due to the microcolumnar structure of LNI, the spatial resolution is 50 µm. LNI exhibits the high brightness of NaI, as well as excellent neutron-gamma discrimination based on pulse height discrimination and pulse shape discrimination.
LNI is an ideal solution for neutron radiography, tomography, diffraction, and homeland security applications. It is available in sizes up to 8″ in diameter and 1 mm in thickness. RMD can produce significantly larger sizes upon request.
The concentration of 6Li in LNI may be tailored to achieve a desired performance. Additionally, emission can be adjusted using Tl or Eu as a dopant or Tl,Eu as co-dopants. Direct deposition on SiPMs, PDs, or other photo-sensors and wavelength shifting fiber arrays is available.
Perovskites Solar Cells
Research into organic thin film solar cells shows promise, however, efficiencies need to be improved if they are to be commercially viable. In the past several years, organometal halide materials exhibiting the perovskite structure have emerged as promising candidates for thin film solar cells.
The perovskite structure is a cubic lattice with the generic formula ABX3, where A is the organic, B is the metal (Pb, or Sn), and X is the halide atom (iodine, bromine, or chlorine). Perovskite halide based solar cells offer an intriguing developmental roadmap that borrows from the condensed matter physics community of perovskite oxide growers. The chemistry of the perovskite can be tuned by doping atoms or molecules onto the A, or B, sites. The structure can be controlled through careful choices of substrates and growth conditions. With these two simple variations, there is tremendous scope for experimentation and fine-tuning of the electronic and optical properties of the materials. With the organometal halide perovskites, we have only just begun to explore the phase space of this class of materials.
RMD is developing light-weight, flexible photovoltaics for military applications, as well as the broader consumer market. We are focusing on photovoltaic cells based on perovskite halide solar cell materials, which have shown remarkable progress in the past six years as solution processable, low-cost solar cell materials that exhibit high efficiencies. Among existing solar cell technologies, perovskite halides present one of the most promising technologies for achieving efficiencies in excess of 20% at suitable costs and in a lightweight form factor. RMD Inc. has developed flexible perovskite solar cells with efficiencies in excess of 13%.