ABSTRACT
Ultrasensitive and sustainable near-infrared (NIR)-emitting piezoluminescence is observed from noncentrosymmetric and ferroelectric-phase Sr3 Sn2 O7 doped with rare earth Nd3+ ions. Sr3 Sn2 O7 :Nd3+ (SSN) with polar A21 am structure is demonstrated to emit piezoluminescence of wavelength of 800-1500 nm at microstrain levels, which is enhanced by the ferroelectrically polarized charges in the multipiezo material. These discoveries provide new research opportunities to study luminescence properties of multipiezo and piezo-photonic materials, and to explore their potential as novel ultrasensitive probes for deep-imaging of stress distributions in diverse materials and structures including artificial bone and other implanted structures (in vivo, in situ, etc).
ABSTRACT
Brookite TiO2 attracts considerable attention in photocatalysis owing to its superior performance in several photocatalytic reactions. In this work, we investigated the behavior of charge carriers in brookite, rutile, and anatase TiO2 by using photoluminescence (PL) and transient absorption (TA) spectroscopies. PL measurements revealed that brookite TiO2 exhibits a visible and a NIR emission at â¼520 nm and â¼860 nm, respectively. Addition of methanol vapor quenched both the visible and NIR emissions by the hole-consuming reaction of methanol. However, exposure to O2 shows curious behaviors: the visible emission was quenched but the NIR emission was enhanced. These results can be accounted for by the enhancement of upward band bending resulting in the effective separation of electrons and holes into the bulk and the surface, respectively. Furthermore, the shallowly trapped electrons, which are responsible for visible PL, are consumed by O2; hence, the visible emission is quenched. However, in the case of NIR emission, the deeply trapped electrons are responsible and they are mainly located at the surface defects. The O2 adsorption promotes the hole accumulation at the surface and then assists the recombination of these deeply trapped electrons, resulting in the enhancement of the NIR emission. We also found that the lifetime of NIR emission (τ1 = 43 ± 0 ns and τ2 = 589 ± 1 ns) was much longer than that of visible emission (τ1 = 15 ± 0 ns and τ2 = 23 ± 0 ns), since the mobility of these deeply trapped electrons to encounter with holes is lower than that of the shallowly trapped electrons. However, even for this slow NIR emission, the actual lifetime of the deeply trapped electrons estimated by TA (1.5 ± 0.0 µs and 17 ± 0 µs) was one or two orders of magnitude longer, confirming that non-radiative recombination is dominant and it is much slower than radiative recombination: TAS and PL provide detailed information on the radiative and non-radiative recombination processes. The PL of anatase and rutile TiO2 powders was also measured and the difference from brookite TiO2 was discussed.
ABSTRACT
For the pretreatment in order to nano prepare porous carbon from biomass such as bamboo, a mixture of acetic acid and hydrogen peroxide was used for the partial delignification of bamboo. The pretreatment should be effective for the removal of lignin because the lignin percentage after the pretreatment depended on the treatment time and the treatment temperature. For the concentration of the mixture used for the pretreatment in this study, a small amount of lignin (ca. 2 wt%) remained even after a sufficiently-long treatment time. The BET specific surface area of the carbon material prepared by the heat treatment at 800 degrees C for 1 h under flowing N2 was related to the pretreatment conditions, and the specific surface areas of the samples were found to be related to the lignin percentage. The removal of lignin while maintaining the microstructure derived from plant tissue could be the reason for the local maximum of the specific surface area at ca. 5% of the lignin.
Subject(s)
Biomass , Carbon/chemistry , Lignin/chemistry , Nanopores , Hydrolysis , Kinetics , Nitrogen/chemistry , TemperatureABSTRACT
The elastico-mechanoluminescence (EML) properties of CaZnOS:Mn2+ are investigated. The CaZnOS:Mn2+/epoxy resin composite can simultaneously "feel" (sense) and "see" (image) various types of mechanical stress over a wide energy and frequency range (ultrasonic vibration, impact, friction and compression) as an intense red emission (610 nm) from Mn2+ ions. Further, the accurate linear relation between emission intensity and different stress parameters (intensity, energy and deformation rate) are confirmed. The EML mechanism is explained using a piezoelectrically induced trapped carrier excitation mode. All the results imply that CaZnOS:Mn2+ has potential as a stress probe to sense and image multiple mechanical stresses and decipher the stress intensity distribution.
