Nd3+-sensitized quenching-shield sandwich-structured upconversion nanoparticles are reported, which exhibit highly efficient upconversion photoluminescence under excitation by an 800 nm continuous-wave laser. The transition-layer structure is essential to bridge energy transfer from the sensitizer to the activator and simultaneously block energy back-transfer from the activator to the sensitizer. These 800 nm-excited upconversion nanoparticles are a key step toward the development of upconversion nanophosphors for biological applications.

We report on analysis of observations of the bright transient X-ray pulsar Swift J0243.6+6124 obtained during its 2017-2018 giant outburst with Insight-HXMT, NuSTAR, and Swift observatories. We focus on the discovery of a sharp state transition of the timing and spectral properties of the source at super-Eddington accretion rates, which we associate with the transition of the accretion disk to a radiation pressure dominated (RPD) state, the first ever directly observed for magnetized neutron star. This transition occurs at slightly higher luminosity compared to already reported transition of the source from sub- to super-critical accretion regime associate with onset of an accretion column. We argue that this scenario can only be realized for comparatively weakly magnetized neutron star, not dissimilar to other ultra-luminous X-ray pulsars (ULPs), which accrete at similar rates. Further evidence for this conclusion is provided by the non-detection of the transition to the propeller state in quiescence which strongly implies compact magnetosphere and thus rules out magnetar-like fields.

Freshly vacuum-evaporated, neat amorphous MoO3 thin films exhibit only UV photochromism. Visible-light photochromism is induced in these films when they are cathodically polarized for a short duration in a nonaqueous electrolyte. The efficiencies of the UV and visible-light photochromism of the MoO3 thin films increase at least 2-fold when they are coated with a thin layer (∼20-nm thickness) of Au or Pt. The enhancement in photochromism is attributed to the presence of a large Schottky barrier at the metal−semiconductor interface, which facilitates electron capture by Au or Pt. The electron capture by the metal produces a longer electron−hole separation lifetime, thereby enhancing the photochromic process. For the electrochromic process, the coloring and bleaching current densities for the MoO3/Au thin-film electrode are about 1.5 and 2.0 times larger than the respective current densities for the MoO3 thin-film electrode. The enhancement in electrochromism is ascribed to the electrocatalytic effect of the gold overlayer. The benefits of surface modifications are (1) inhibition of electron−hole recombination, which enhances photochromism, (2) enhancement of electrochromism, and (3) inhibition of corrosion reaction of surface MoO3.