We have successfully grown SnS single crystals by the slow cooling method in a horizontal temperature gradient furnace, AgBiS2 single crystals by the slow cooling method, GeS single crystals by the vapor transport method using a molten GeS source, and GaS single crystals by the Bridgman method.
GaS single crystals have been found to have a transmission range of up to 14 µm and can be used as an optical material in the infrared. SnS, GeS, and GaS are also 2D materials.
2D SnS is theoretically predicted to have piezoelectric properties comparable to Pb(Zr, Ti)O3:PZT. We are jointly investigating the piezoelectric properties of 2D SnS using SnS single crystals.
Optical single crystals group
STAFF
Group leader
Group members
AIM and GOAL
- Design, bulk growth, and characterization of new single crystal materials
- Development of proper growth techniques to achieve the best material properties
APPROACH
- A wide range of crystals for optical applications is covered: laser and nonlinear optical crystals, magneto-optical crystals, scintillator/dosimeter crystals, wide bandgap semiconductor, piezoelectric and ferroelectric single crystals, etc.
- Our current main research targets are: Single crystal phosphors for high-brightness lighting devices. Faraday rotators for optical isolators used for laser machinery. Piezoelectric crystals for high temperature use such as combustion pressure sensors. Gallium oxide as novel wide bandgap semiconductor. Chalcogenides for IR optical applications.
- Collaboration with universities, national institutes and industries are actively promoted, and the international cooperation is also actively pursued in order to promote new viewpoints and original ideas.
FIG 1 CZ-grown Ce:YAG single crystal phosphor. This novel phosphor exhibits superior internal quantum efficiency compared with conventional ceramic based phosphors even at high temperatures. Therefore, this is suitable for high-brightness white lighting applications.
FIG 2 Large-size TSLAG single crystal. This novel crystal shows large Faraday rotation angle and high transmittance, and therefore exhibits better performance for optical isolators which protect the light source of laser machinery.
NAKAMURA, Masaru
mail：NAKAMURA.Masaru@nims.go.jp
Search and growth of high-performance sulfide single crystals
Overview
Sulfides have excellent optical properties, allowing a wider transparency range into the infrared range compared to oxides. Therefore, they are promising materials for infrared optical devices. In addition to optical applications, they are also expected to be used as thermoelectric and solar cell materials. In addition, they have attracted renewed attention as 2D materials in recent years. In this research, high-purity sulfur purified by distillation has been used.
SnS, AgBiS2, GeS, and GaS single crystals were successfully grown.
Characteristics
The high performance of sulfides is as follows.
- Over 10µm transmission range
- Non-toxic and excellent thermoelectric properties
- Rediscovered as a 2D material
Major reserch
summary
We have successfully grown various sulfide single crystals using different methods. As a result, we have mainly obtained the following sulfide single crystals.
In the future, we will search for sulfides with more high-performance properties and develop methods for growing their single crystals.
- SnS single crystals (applications: 2D materials, solar cells)
- AgBiS2 single crystals (applications: thermoelectric elements, solar cells)
- GeS single crystals (applications: 2D materials)
- GaS single crystals (applications: infrared optical devices, 2D materials)
VILLORA, Garcia
mail：VILLORA.Garcia@nims.go.jp
Crystals for optical isolators and high-brightness white light sources
Overview
- Optical isolators are needed for laser machinery, marking, and high-power LDs.
New novel Faraday rotators are demanded for higher laser powers and shorter wavelengths. - Ceramic powder phosphors are used for white lighting by excitation with blue LEDs/LDs.
All-inorganic efficient phosphors are needed for high-brightness applications.
Characteristics
- Improvement of Tb-garnets for IR Faraday rotators and development of new UV-visible Faraday rotators.
- Development of new binder-free yellow-green single-crystal phosphors with high conversion efficiency and high thermal stability to realize high-brightness white LEDs/LDs.
Major reserch
- High optical quality fluoride and oxide single-crystals are grown by the Czochralski and Bridgman techniques.
- Grown crystals and oriented, cut, and polished for characterization in terms of crystalline quality and optical properties.
- Prototypes are fabricated to analyze the performance of actual devices and to get feedback for further development.
summary
- Tb-Sc-garnets are already incorporated into Yb-amplified fiber-lasers by Fujikura Ltd.
- CeF3 is implemented in commercial UV-VIS optical isolators.
- SCPs are already utilized in high-brightness light sources, and further expansion is foreseen in the next generations of projectors and headlights.
YUAN, Dongsheng
mail：YUAN.Dongsheng@nims.go.jp
Oxide and halide single-crystals for radiation detection
Overview
Inorganic single-crystal radiation detectors are widely employed in the fields of homeland security, industrial nondestructive inspection, nuclear medicine imaging, and high-energy physics. Even though depending on the specific application the required properties vary, there is a general market demand for scintillators that are chemically stable, cost-effective, and efficient.
Two distinct application-oriented topics are mainly focused: (1) thermal neutron scintillators for handheld detectors (stable oxides instead of the currently used highly hygroscopic halides) and (2) new X/γ-rays scintillators (good air-stability, high light yield, excellent non-proportionality).
Characteristics
- Development of non-hygroscopic thermal neutron scintillator Ce:Li6Y(BO3)3 (LYBO): (1) greatly reduced scattering centers for the first time, (2) high light yield over 4000 ph/n, (3) inch-size bulk crystal growth.
- Finding of a new chemically-stable and bright halide scintillator Cs3Cu2I5(CCI) that can be grown into large-size single crystals via the melt method.
Major reserch 1
The previously disregarded Ce: LYBO due to extremely low light yield has been developed using the strategies of proper Ce3+-doping and drastic reduction of scattering centers, with the light yield being comparable to the reference Li-glass (GS20).
Major reserch2
Large-size crystal growth of the new iodide scintillator CCI is achieved by the melt method that is practicable in mass production.
Tl:CCI exhibits a high light yield, good energy resolution, and excellent non-proportionally (less than 3%) while being chemically-stable compared with the commercial halide scintillators such as NaI and SrI2.
summary
- High light yield of Ce:LYBO makes this family practically promising for handheld neutron detection. The successful strategies will be extrapolated to other low melting-point oxide scintillators.
- The stable and bright scintillator CCI has gained great attention worldwide. After doping, the optimized Tl:CCI has been found even brighter that the commercial Eu:SrI2.
Fields of Electronic and Photofunctional Materials Research Center
Ultra-wide Bandgap Semiconductors Group
Optical Single Crystals Group