Metal-organic frameworks (MOFs) enable the design of host-guest systems with specific properties.I nt his work, we showh ow the confinement of anthracene in aw ellchosen MOF host leads to reversible yellow-to-purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene,e ither in pure form or adsorbed in other porous hosts.The photoresponse of the hostguest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry,c onnectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.

Vacancy‐type defects in Mg‐implanted GaN are probed using monoenergetic positron beams. Mg+ ions are implanted to provide a 500‐nm‐deep box profile with Mg concentrations, [Mg], of 1 × 1017–1 × 1019 cm−3 at room temperature. In the as‐implanted samples, the major defect species is a complex of a Ga vacancy (VGa) and a nitrogen vacancy (VN). After annealing above 1000 °C, the major defect species is changed to vacancy clusters due to vacancy agglomeration. This agglomeration is suppressed, and the agglomeration onset temperature is decreased with a decreasing [Mg]. For samples with [Mg] ≥ 1 × 1018 cm−3, the trapping rate of positrons by vacancy‐type defects decrease after annealing above 1100–1200 °C. This decreases is attributed to the change in the defect charge states from neutral to positive due to a downward shift of the Fermi level. The carrier trapping/detrapping properties of the vacancy‐type defects and their time dependences are also revealed.

At low humidity (<30 RH%), water molecules begin to fill the intermolecular spaces in the membrane. At high humidity (80 RH%) the membrane swells; the free volume size increases.