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Two-dimensional (2D) Ruddlesden–Popper (RP) perovskite materials have been widely studied as optoelectronic and photonic devices because of the combination of advantages of perovskites and the unique excitonic properties in the 2D limit. However, thin 2D perovskite flakes, in general, suffer from a weak photoluminescence (PL) emission because of surface defects related to nonradiative recombinations. Here, we demonstrate that the PL of thin 2D RP perovskites can be enhanced by the introduction of spiro-OMeTAD, which effectively passivates the surface defects of RP perovskites. By steady-state and time-resolved PL spectroscopy, we investigate the interaction between spiro-OMeTAD and RP perovskite flakes with different thicknesses and find that along with the enhanced PL intensity, the PL lifetime is prolonged, which agrees with the reduction in nonradiative recombination. In contrast, for thicker perovskite flakes, the spiro-OMeTAD leads to PL quenching and a shortened PL lifetime, due to the reduced surface effect and the formation of a type-II band alignment with the perovskites. Our research provides an effective method to enhance the PL emission of thin 2D RP perovskites, which could promote the future device applications of RP perovskites.

Salmonellacontamination in a dry processing facility frequently requires removal methods that are nonaqueous. Removal of pathogens from food processing systems with a purge of uncontaminated dry food materials has been proposed; however, little is known with respect to efficacy. In this study, survival of Salmonellaon inert contact surfaces and transfer of Salmonellafrom inert contact surfaces to low-moisture foods were evaluated. Six stainless steel and polymeric food contact material types, in bead form, were contaminated at 11 log CFU/mL and then stored at two temperatures, 25 and 4°C, for 6 months. Simultaneously, three dry food materials or ingredients were used to remove Salmonellafrom contaminated beads. Wheat flour, cornmeal, and NaCl (1 g each) were mechanically mixed with 3 beads of each material type. The rate of microbial transfer from contaminated beads to food materials was measured. Further experimentation using multiple transfers was applied on two representative beads types, 316 stainless steel and polypropylene, representing common surface contact materials used in processing equipment. Survival of Salmonellaon beads depended on storage temperature, with longer survival (P< 0.05) at 4°C than at 25°C, but survival was not influenced by type of bead material. Transfer of Salmonellafrom stainless steel beads to flour was significantly greater (P< 0.05) than from plastic. Transfer rates from stainless steel to wheat flour, cornmeal, and NaCl were measured as −0.5713, −0.2592, and −1.4221 log CFU of Salmonellaremoved per cm2per g of clean material used. Transfer rates from polypropylene to whole wheat flour, cornmeal, and NaCl were more than 10-fold lower at −0.0156, −0.0148, and −0.0129 log CFU of Salmonellaremoved per cm2per g of clean material used. These results indicate that although material type may not influence Salmonellasurvival during storage, Salmonellais more easily removed from stainless steel than polypropylene.