Scintillators are materials that convert radiation energy into light. Researchers at University of Tsukuba have made a groundbreaking discovery: Eu (Europium)-doped CaF₂ crystals, a type of scintillator, that emit more light at longer wavelengths when irradiated with alpha particles as compared to X-rays. This finding suggests the potential for identifying radiation types based on emission wavelength.

Tsukuba, Japan—Scintillators convert radiation energy into light and are utilized in a variety of fields including medicine and security. Of the many scintillators, Eu (europium)-doped CaF₂ (calcium fluoride) crystals stand out due to their high light yield (approximately 20,000 photons/MeV), excellent optical transparency, and chemical stability.

Previously, the emission wavelength of scintillators was thought to be independent of the type of radiation. In this study, multiple CaF₂ crystals with different Eu doping concentrations were synthesized and irradiated with alpha particles and X-rays to investigate systematically the color (wavelength) and intensity of the emitted light. The results showed that the ratio of Eu²⁺-induced emission (wavelength: ~420 nm) to Eu³⁺-induced emission (wavelength: 590-695 nm) varies depending on the type of radiation. Moreover, for the same sample, when Eu²⁺ emission was held constant, Eu³⁺ emission was found to be approximately twice as strong under α particle irradiation as compared to X-ray irradiation. This suggests that differences in light color could be used to identify radiation types, which has the potential for use with unique applications, including dose measurements in complex environments such as nuclear facility decommissioning sites.

These findings are expected to pave the way for new particle identification methods and next-generation radiation detection technologies. Moving forward, we aim to develop a technique that records the tracks of passing radiation in color by integrating this method with an optical system using lenses, thereby creating a means to identify particle types, such as alpha particles and X-rays, based on color.

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This study was financially supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grants (grant numbers JP23K17685 and JP25K22021), as well as by the Konica Minolta Science and Technology Foundation.

Original Paper

Title of original paper:

Emission Characteristics of Eu²⁺ and Eu³⁺ under X-Ray and Alpha Irradiation in Eu-Doped CaF₂ Crystals

Journal:

Scientific Reports

DOI:

10.1038/s41598-025-17570-5

Correspondence

Assistant Professor IIDA Takashi
Institute of Pure and Applied Sciences, University of Tsukuba

Project Associate Professor YOSHINO Masao
Institute for Materials Research, Tohoku University

Related Link

Institute of Pure and Applied Sciences