Showing papers by "Setsuhisa Tanabe published in 2023"

Photochromism and Long Persistent Luminescence in Pr3+‐Doped Garnet Transparent Ceramic via UV or Blue Light Up‐Conversion Charging

Abstract: Multifunctional phosphors with photochromism and persistent luminescent (PersL) properties have attracted increasing interest owing to the capability of absorbing the photon energy and trapping the generated carriers via defects. However, the opacity of materials compromises the enhancement of photochromism and PersL properties; besides, the need of high energy excitation light source limits their applicability. To bridge these obstacles, Pr3+‐doped Y3Al2Ga3O12 transparent ceramic with in‐line transmittance over 80% at 1,800 nm is reported, which exhibits strong red PersL after several minutes UV light or blue light up‐conversion charging. The luminance duration time can reach >7 h at 0.32 mcd m−2 threshold value after UV light charging. Interestingly, the phosphor also displays photochromic properties with robust fatigue resistance, i.e., the color changes from light green to red by UV/blue light illumination and is bleached at 300 °C. The nature of trap centers, trapping and detrapping processes is explored based on thermoluminescence and electron spin resonance. Finally, the mechanism of photochromism and PersL is discussed by using vacuum referred binding energy diagram. This work opens new avenues for future research on multifunctional materials and brings potential applications in optical information encryption media and optical sensors.

Addressing Current Challenges in OSL Dosimetry Using MgB4O7:Ce,Li: State of the Art, Limitations and Avenues of Research

Abstract: The objective of this work is to review and assess the potential of MgB4O7:Ce,Li to fill in the gaps where the need for a new material for optically stimulated luminescence (OSL) dosimetry has been identified. We offer a critical assessment of the operational properties of MgB4O7:Ce,Li for OSL dosimetry, as reviewed in the literature and complemented by measurements of thermoluminescence spectroscopy, sensitivity, thermal stability, lifetime of the luminescence emission, dose response at high doses (>1000 Gy), fading and bleachability. Overall, compared with Al2O3:C, for example, MgB4O7:Ce,Li shows a comparable OSL signal intensity following exposure to ionizing radiation, a higher saturation limit (ca 7000 Gy) and a shorter luminescence lifetime (31.5 ns). MgB4O7:Ce,Li is, however, not yet an optimum material for OSL dosimetry, as it exhibits anomalous fading and shallow traps. Further optimization is therefore needed, and possible avenues of investigation encompass gaining a better understanding of the roles of the synthesis route and dopants and of the nature of defects.

Neodymium(III)-doped Y3Al2Ga3O12 garnet for multipurpose ratiometric thermometry: From cryogenic to high temperature sensing

Abstract: Nd3+-doped Y3Al2Ga3O12 garnet ceramic pellet was prepared by solid state reaction and used as prototype to investigate the potential of Nd3+-activated garnet phosphors as Boltzmann thermometers for cryogenic and high temperature ranges. Despite the conventional use of the near-infrared emitting Nd3+-activated phosphors for biological applications, their real use is hindered by a low sensitivity in the physiological temperature range. Instead, the photoluminescence analysis in the 100–800 K range demonstrated interesting performances in both the cryogenic and high temperature ranges. Indeed, by taking advantage of the Stark levels of 4F3/2 (Z-levels) and the ratio between the emission from the 4F5/2 and the 4F3/2 excited states is possible to build two reliable Boltzmann thermometers in the same material working in the cryogenic temperature range (100–220 K) and at high temperatures (300–800 K), respectively.