Scintillation Response of Nd-Doped LaMgAl11O19 Single Crystals Emitting NIR Photons for High-Dose Monitoring.

The Nd-doped LaMgAl11O19 single crystals were synthesized by the floating zone method, and the photoluminescence and scintillation properties were evaluated. Under X-ray irradiation, several sharp emission peaks due to the 4f-4f transitions of Nd3+ were observed at 900, 1060, and 1340 nm in the near-infrared range, and the decay curves show the typical decay time for Nd3+. The samples show good afterglow properties comparable with practical X-ray scintillators. The 1% and 3% Nd-doped LaMgAl11O19 samples show a good linearity in the dynamic range from 6-60,000 mGy/h.

Scintillation Properties of Ba3RE(PO4)3 Single Crystals (RE = Y, La, Lu).

Eulytite-type Ba3RE(PO4)3 (RE = Y, La, and Lu) single crystals were synthesized by the floating zone method, and their scintillation properties were investigated. The powder X-ray diffraction measurement revealed that the single phase of Ba3RE(PO4)3 samples were successfully synthesized. The samples exhibited a luminescence peak due to self-trapped exciton at around 400 nm under vacuum ultraviolet and X-ray irradiation. The X-ray-induced scintillation decay time constants of the samples were several microseconds at room temperature. In the 241Am α-ray irradiated pulse height spectra, all the samples showed a clear full energy peak, and the absolute light yields of the Ba3Y(PO4)3, Ba3La(PO4)3, and Ba3Lu(PO4)3 single crystals were estimated to be 960, 1160, and 1220 ph/5.5 MeV-α, with a typical error of ±10%, respectively. The scintillation light yields of the Ba3RE(PO4)3 have been quantitatively clarified for the first time.

Ce-doping effect on dosimetric properties of mullite single crystals synthesized by the floating zone method.

We synthesized the 0.1, 0.5, 1.0, and 1.5% Ce-doped mullite single crystals by the floating zone method and evaluated their photoluminescence (PL) and thermally stimulated luminescence (TSL) properties. The single-phase orthorhombic structure was confirmed in all the samples from powder X-ray diffraction patterns. The transmittance spectra of all the samples showed the absorption related to the 4f-5d transitions of Ce3+ ions and optical band gap of mullite. The Ce-doped mullite single crystals had the PL attributed to the 5d-4f transitions of Ce3+ ions. In TSL properties, TSL glow curves had the glow peaks at 250 and 370 °C, and TSL spectra heated at 250 and 370 °C had the peak at around 390 nm owing to the Ce3+ ions. TSL dose response functions showed linear response from 0.01 mGy to 10 Gy for the 1.0% Ce-doped mullite single crystal and from 0.1 mGy to 10 Gy for the 0.1, 0.5, and 1.5% Ce-doped ones. The 1.0% Ce-doped mullite single crystal could be used multiple times for dosimetry. In addition, the TSL intensity of the 1.0% Ce-doped mullite single crystal after 7 days from X-ray irradiation was about 82.4% from immediately one after X-ray irradiation.

X-ray-Induced Scintillation Properties of Nd-Doped Bi4Si3O12 Crystals in Visible and Near-Infrared Regions.

Undoped, 0.5, 1.0, and 2.0% Nd-doped Bi4Si3O12 (BSO) crystals were synthesized by the floating zone method. Regarding photoluminescence (PL) properties, all samples had emission peaks due to the 6p-6s transitions of Bi3+ ions. In addition, the Nd-doped samples had emission peaks due to the 4f-4f transitions of Nd3+ ions as well. The PL quantum yield of the 0.5, 1.0, and 2.0% Nd-doped samples in the near-infrared range were 67.9, 73.0, and 56.6%, respectively. Regarding X-ray-induced scintillation properties, all samples showed emission properties similar to PL. Afterglow levels at 20 ms after X-ray irradiation of the undoped, 0.5, 1.0, and 2.0% Nd-doped samples were 192.3, 205.9, 228.2, and 315.4 ppm, respectively. Dose rate response functions had good linearity from 0.006 to 60 Gy/h for the 1.0% Nd-doped BSO sample and from 0.03 to 60 Gy/h for the other samples.

Remote control of neural function by X-ray-induced scintillation.

Scintillators emit visible luminescence when irradiated with X-rays. Given the unlimited tissue penetration of X-rays, the employment of scintillators could enable remote optogenetic control of neural functions at any depth of the brain. Here we show that a yellow-emitting inorganic scintillator, Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG), can effectively activate red-shifted excitatory and inhibitory opsins, ChRmine and GtACR1, respectively. Using injectable Ce:GAGG microparticles, we successfully activated and inhibited midbrain dopamine neurons in freely moving mice by X-ray irradiation, producing bidirectional modulation of place preference behavior. Ce:GAGG microparticles are non-cytotoxic and biocompatible, allowing for chronic implantation. Pulsed X-ray irradiation at a clinical dose level is sufficient to elicit behavioral changes without reducing the number of radiosensitive cells in the brain and bone marrow. Thus, scintillator-mediated optogenetics enables minimally invasive, wireless control of cellular functions at any tissue depth in living animals, expanding X-ray applications to functional studies of biology and medicine.

Oxidation suppression of Cu in alkaline aluminophosphate glass and the effects for radiation-induced luminescence characteristics.

A glass phosphor is an attractive material for applications in radiation detections because of its high workability and availability with a wide range of chemical compositions. Recently, X-ray-induced luminescence of glasses containing various luminescent activators are actively investigated worldwide. In applications as phosphor, tailoring valence state of activators, which can take multiple valence states in glass, is very important. In this research, we studied effects of glass melting atmosphere on the valence state of copper-activator ion in alkaline aluminophosphate glasses and the radiation-induced luminescence characteristics. Optical absorption and X-ray absorption near edge structure spectra of Cu-doped glasses showed that the glass fused in Ar atmosphere contains higher concentration of Cu+ than those prepared in air. In addition, the presence of Cu+ enhances the photoluminescence (PL) quantum yield and PL kinetic constant. Furthermore, the increase of Cu+ concentration resulted an improvement of the X-ray-induced scintillation and thermally-stimulated luminescence intensity.

Photosynergetic amplification of radiation input: from efficient UV induced cycloreversion to sensitive X-ray detection.

Five photochromic terarylenes which show reversible photocyclisation and cycloreversion with relatively high quantum yields are presented. Some of these have been observed to undergo a highly efficient cycloreversion cascade process from their coloured, closed forms to their uncoloured open forms that leads to cycloreversion quantum yields significantly larger than unity. This cascade effect can been induced with both chemical and X-ray initiation; the limit of detection from X-ray initiation has been tested and is comparable to existing systems with detection observed at values as low as 0.3 mGy.

X-ray-induced Scintillation Governed by Energy Transfer Process in Glasses.

The efficiency of X-ray-induced scintillation in glasses roughly depends on both the effective atomic number Zeff and the photoluminescence quantum efficiency Qeff of glass, which are useful tools for searching high-performance phosphors. Here, we demonstrate that the energy transfer from host to activators is also an important factor for attaining high scintillation efficiency in Ce-doped oxide glasses. The scintillation intensity of glasses with coexisting fractions of Ce3+ and Ce4+ species is found to be higher than that of a pure-Ce3+-containing glass with a lower Zeff value. Values of total attenuation of each sample indicate that there is a non-linear correlation between the scintillation intensity and the product of total attenuation and Qeff. The obtained results illustrate the difficulty in understanding the luminescence induced by ionizing radiation, including the energy absorption and subsequent energy transfer. Our findings may provide a new approach for synthesizing novel scintillators by tailoring the local structure.

Scintillating Organic-Inorganic Layered Perovskite-type Compounds and the Gamma-ray Detection Capabilities.

We investigated scintillation properties of organic-inorganic layered perovskite-type compounds under gamma-ray and X-ray irradiation. A crystal of the hybrid compounds with phenethyl amine (17 × 23 × 4 mm) was successfully fabricated by the poor-solvent diffusion method. The bulk sample showed superior scintillation properties with notably high light yield (14,000 photons per MeV) under gamma-rays and very fast decay time (11 ns). The light yield was about 1.4 time higher than that of common inorganic material (GSO:Ce) confirmed under 137Cs and 57Co gamma-rays. In fact, the scintillation light yield was the highest among the organic-inorganic hybrid scintillators. Moreover, it is suggested that the light yield of the crystal was proportional with the gamma-ray energy across 122-662 keV. In addition, the scintillation from the crystal had a lifetime of 11 ns which was much faster than that of GSO:Ce (48 ns) under X-ray irradiation. These results suggest that organic-inorganic layered perovskite-type compounds are promising scintillator for gamma-ray detection.