[en] Highlights: • Elucidating the crystalline formation of rare earth phosphate. • Mechanistic understanding of La³⁺ substitution in YPO₄ host matrix and optical emission. • Delineating the correlation of the structural lattice distortion and enhanced UV-C emission. • Fundamental designing principles of inorganic phosphors. -- Abstract: The UV-C emission with a spectral range of 200–280 nm is of paramount importance in the germicidal and medical applications for disinfection, sterilization, and deactivation of microorganisms such as bacteria and virus considering current global pandemic crisis of coronavirus (COVID-19). Such intense UV-C radiation (4.4–6.2 eV) can be often generated using Pr³⁺ activators (as a result of their electronic transition [Xe]4f¹5d¹→[Xe]4f²) doped in crystalline inorganic host matrices. In this regard, Pr³⁺-activated rare earth phosphates have been intensively studied as a model system of UV-C emitters thus far. Here, we have prepared three different representative crystalline UV-C phosphors of YPO₄:Pr³⁺ (tetragonal), LaPO₄:Pr³⁺ (monoclinic), and La-substituted YPO₄:Pr³⁺ (tetragonal), respectively, and further investigated the effect of La substitution in YPO₄ crystal structures on UV-C emitting properties. The structural lattice distortion in the local environment of activator Pr³⁺ cations induced by La substitution indeed impacts on the UV-C emitting properties. Small amount of substitutional doping of La³⁺ (ca. 5 mol.%) in Y site of YPO₄ enhances the UV-C emission intensity by a two-fold of magnitude recorded under 225 nm excitation (photoluminescence) and cathode ray (cathodeluminescence). This finding can provide a fundamental designing principle of inorganic phosphor materials to enhance the emitting properties of activators, directly influenced by local environment and symmetry of the crystal structures.

[en] In respiratory-induced proton therapy, the accuracy of tracking system and beam controlling is more important than photon therapy. Therefore, a high accuracy motion tracking system that can track internal marker and external surrogate is needed. In this research, our team has installed internal and external marker tracking system at our institution’s proton therapy system, and tested the scanning with gating according to the position of marker. The results demonstrate that the developed in-house external/internal marker based gating system can be clinically used for proton therapy system for moving tumor treatment.

[en] In this study, the noise level, effective atomic number (Zeff), accuracy of the computed tomography (CT) number, and the CT number to the relative electron density ED conversion curve were estimated for virtual monochromatic energy and polychromatic energy. These values were compared to the theoretically predicted values to investigate the feasibility of the use of dual-energy CT in routine radiation therapy planning. The accuracies of the parameters were within the range of acceptability. These results can serve as a stepping stone toward the routine use of dual-energy CT in radiotherapy planning.

[en] GATE (Geant4 Application Tomography Emission) Monte Carlo simulations have been successful in the application of emission tomography for precise modeling of various physical processes. Most previous studies on Monte Carlo simulations have only involved performance assessments using virtual phantoms. Although that allows the performance of simulated positron emission tomography (PET) to be evaluated, it does not reflect the reality of practical conditions. This restriction causes substantial drawbacks in GATE simulations of real situations. To overcome the described limitation and to provide a method to enable simulation research relevant to clinically important issues, we conducted a GATE simulation using real data from a scanner rather than a virtual phantom and evaluated the scanner is performance. For that purpose, the system and the geometry of a commercial GE PET/ CT (computed tomography) scanner, BGO-based Discovery 600 (D600), was developed for the first time. The performance of the modeled PET system was evaluated by using the National Electrical Manufacturers Association NEMA NU 2-2007 protocols and results were compared with those of the reference data. The sensitivity, scatter fraction, noise-equivalent count rate (NECR), and resolution were estimated by using the protocol of the NEMA NU2-2007. Sensitivities were 9.01 cps/kBq at 0 cm and 9.43 cps/kBq at 10 cm. Scatter fractions were 39.5%. The NECR peak was 89.7 kcps at 14.7 kBq/cc. Resolutions were 4.8 mm in the transaxial plane and 5.9 mm in the axial plane at 1 cm, and 6.2 mm in the transaxial plane and 6.4 mm in the axial plane at 10 cm. The resolutions exceeded the limited value provided by the manufacturer. The uniformity phantom was simulated using the CT and the PET data. The output data in a ROOT format were converted and then reconstructed by using the C program and STIR (Software for Tomographic Image Reconstruction). The reconstructed images of the simulated uniformity phantom data had comparable quality even though improvement in the quality is still required. In conclusion, we have demonstrated a successful simulation of a PET system by using scanned data. In future studies, the parameters that alter the imaging conditions, such as patient movement and physiological change, need to be studied.

[en] Highlights: • Lead halide perovskite nanocrystals were synthesized via hot injection. • Perovskite nanocrystals remain highly optically stable after purification. • Perovskite nanocrystals afford sensitive and specific latent fingerprint detection. Latent fingerprints (LFPs) are one of the most important forms of evidence in crime scenes due to the uniqueness and permanence of the friction ridges in fingerprints. Therefore, an efficient method to detect LFPs is crucial in forensic science. However, there remain several challenges with traditional detection strategies including low sensitivity, low contrast, high background, and complicated processing steps. In order to overcome these drawbacks, we present an approach for developing latent fingerprints using stabilized CsPbBr₃ perovskite nanocrystals (NCs) as solid-state nanopowders. We demonstrate the superior optical stability of CsPbBr₃ NCs with respect to absorption, photoluminescence (PL), and fluorescence lifetime. We then used these highly stable, fluorescent CsPbBr₃ NCs as a powder dusting material to develop LFPs on diverse surfaces. The stable optical properties and hydrophobic surface of the CsPbBr₃ NC nanopowder permitted high resolution images from which unique features of friction ridge arrangements with first, second, and third-level LFP details can be obtained within minutes.

[en] Highlights: • Cu-doped Bi₂Te_2.7Se_0.3 was first synthesized by using Cu nanoparticle precursor. • The power factor is enhanced by the substitutional Cu doping in quintuple layers. • Substantial reduction of electronic thermal conductivity originates from Cu doping. • Average zT value at 300–500 K for 2% Cu–Bi₂Te_2.7Se_0.3 increased to 0.79. • The power generation efficiency can be enhanced by 25% from the pristine sample. -- Abstract: Bi-Te-based materials have been used for room-temperature thermoelectric applications. However, n-type Bi₂(Te,Se)₃ thermoelectric alloys show a limited conversion efficiency, as compared to their p-type counterparts, thus hindering further widespread room-temperature applications. In this study, we investigated the enhanced thermoelectric properties of n-type Bi₂(Te,Se)₃ materials by the addition of Cu nanoparticles via a conventional high-energy ball milling process. The electrical and thermal transport properties were modulated by changing the amount of Cu nanoparticles. The power factor was enhanced by controlling the carrier, and the total thermal conductivity was reduced mainly due to the reduction in electronic thermal conductivity. Thus, dimensionless thermoelectric figure of merit (zT) at room temperature was enhanced for the Cu-added samples, and the highest zT value of 0.85 at 375 K was achieved in 2% Cu-doped Bi₂Te_2.7Se_0.3. The average zT (zT_avg) value between room temperature and 500 K was 0.79 for the 2% Cu-doped Bi₂Te_2.7Se_0.3, which was 20% higher than that of the pristine Bi₂Te_2.7Se_0.3, whereas a zT higher than 0.80 was sustained from room temperature to ~450 K. These results can lead to a high thermoelectric power generation efficiency of 7.6% at ΔT = 200 K.

[en] Target motion–induced uncertainty in particle therapy is more complicated than that in X-ray therapy, requiring more accurate motion management. Therefore, a hybrid motion-tracking system that can track internal tumor motion and as well as an external surrogate of tumor motion was developed. Recently, many correlation tests between internal and external markers in X-ray therapy have been developed; however, the accuracy of such internal/external marker tracking systems, especially in particle therapy, has not yet been sufficiently tested. In this article, the process of installing an in-house hybrid internal/external motion-tracking system is described and the accuracy level of tracking system was acquired. Our results demonstrated that the developed in-house external/internal combined tracking system has submillimeter accuracy, and can be clinically used as a particle therapy system as well as a simulation system for moving tumor treatment.