Brookite TiO2 is a promising material for active photocatalysts. However, the principal mechanism that determines the distinctive photocatalytic activity between anatase, rutile, and brookite TiO2 has not yet been fully elucidated. Therefore, in this work, we studied the behavior of photogenerated electrons and holes in these TiO2 powders by using femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy. We found that most of the photogenerated electrons in brookite TiO2 are trapped at powder defects within a few ps. This electron trapping decreases the number of surviving free electrons, but it extends the lifetime of holes as well as the trapped electrons because the probability of electrons to encounter holes is decreased by this electron-trapping. As a result, the number of surviving holes increases, which is beneficial for photocatalytic oxidation. In contrast, the reactivity of electrons is decreased to some extent by trapping, but they still remain active for photocatalytic reductions. Electron trapping also takes place on anatase and rutile TiO2 powders, but the trap-depth in anatase is too shallow to extend the lifetime of holes and that of rutile is too deep than the thermal energy (kT) at room temperature for the electron-consuming reactions. As a result of the moderate depth of the electron trap in brookite, both electrons and holes are reactive for photocatalytic reductions and oxidations. These results have clearly demonstrated that the presence of an appropriate depth of the electron trap can effectively contribute to enhance the overall photocatalytic activity.

Graphitic carbon nitride (g-C 3 N 4) has attracted much attention as a metal-free semiconductor having visible light absorption and relatively high chemical stability under visible light irradiation. Graphitic carbon nitride (g-C 3 N 4) and boron-doped g-C 3 N 4 (B-doped g-C 3 N 4 , BCNx) were prepared by heating melamine and a mixture of dicyanodiamide and BH 3 NH 3 , respectively. X-ray diffraction, a Brunauer, Emmett and Teller (BET) apparatus, and UV-vis spectra were used to analyze the physical properties of the prepared samples. Electrodes of these samples were prepared by using the electrophoresis method. X-ray photoelectron spectroscopy analyses confirmed the incorporation of boron atoms in the g-C 3 N 4 framework as well as the amount of boron atoms. Au, Ag or Rh as a co-catalyst was coated on the surface of g-C 3 N 4 and B-doped g-C 3 N 4 by using the magnetron sputtering method. The photocurrent response was observed using a solar simulator as a light source. The photocurrent response of B-doped g-C 3 N 4 was about 5-times larger than that of pure g-C 3 N 4. B-doped g-C 3 N 4 coated with Rh as a co-catalyst showed the highest photocurrent response under solar light irradiation, its photocurrent being about 10-times larger than that of original g-C 3 N 4. Under photoelectrochemical conditions, we also observed the products in gas phase and aqueous phase. C 2 H 5 OH was observed as a main product, while small amounts of CO and H 2 were observed in gas phase. We also discuss the relationship between co-catalysts and photocurrent responses and the carbon source of 3 C 2 H 5 OH as a main product. The source of carbon of C 2 H OH obtained by CO reduction is discussed on the basis of results of a labeling experiment using 13 CO 2 .

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.

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Ultrasensitive and sustainable near‐infrared (NIR)‐emitting piezoluminescence is observed from noncentrosymmetric and ferroelectric‐phase Sr3Sn2O7 doped with rare earth Nd3+ ions. Sr3Sn2O7:Nd3+ (SSN) with polar A21am 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).