Disinfection in public venues and transport as a way to prevent the spread of COVID-19

The article addresses to the epidemiological characteristics of the SARS-CoV-2 coronavirus. It covers detailed features and ways of coronavirus infection spreading in public venues, factors that affect the viability of the Coronaviridae family viruses, and the infection after-effects for people. Methodological and technical means of processing public transport and crowded places in the context of the spread of coronavirus infection (COVID-19) analysis has been carried out. The assessment of inactivating effectiveness of the basic chemical groups of disinfectants (oxygen-active; chloactive; cationic surfactants) is presented. The features of air masses and surfaces disinfection by the ultraviolet irradiation method are described. Special aspects and factors influencing the installations quality are considered, recommendations for the use of UV emitters of various types are given. The given study presents the general concept and current requirements for disinfection measures in public venues and transport in the context of coronavirus infection spreading. Keywords: COVID-19, coronavirus SARS-CoV-2, disinfection, novel coronavirus infection, sanitary epidemic control measures, transport, public venues.

Monolayer-Scale GaN/AlN Multiple Quantum Wells for High Power e-Beam Pumped UV-Emitters in the 240–270 nm Spectral Range

Monolayer (ML)-scale GaN/AlN multiple quantum well (MQW) structures for electron-beam-pumped ultraviolet (UV) emitters are grown on c-sapphire substrates by using plasma-assisted molecular beam epitaxy under controllable metal-rich conditions, which provides the spiral growth of densely packed atomically smooth hillocks without metal droplets. These structures have ML-stepped terrace-like surface topology in the entire QW thickness range from 0.75–7 ML and absence of stress at the well thickness below 2 ML. Satisfactory quantum confinement and mitigating the quantum-confined Stark effect in the stress-free MQW structures enable one to achieve the relatively bright UV cathodoluminescence with a narrow-line (~15 nm) in the sub-250-nm spectral range. The structures with many QWs (up to 400) exhibit the output optical power of ~1 W at 240 nm, when pumped by a standard thermionic-cathode (LaB6) electron gun at an electron energy of 20 keV and a current of 65 mA. This power is increased up to 11.8 W at an average excitation energy of 5 µJ per pulse, generated by the electron gun with a ferroelectric plasma cathode at an electron-beam energy of 12.5 keV and a current of 450 mA.

Localized UV emitters on the surface of β-Ga2O3

Monoclinic gallium oxide (β-Ga2O3) is attracting intense focus as a material for power electronics, thanks to its ultra-wide bandgap (4.5–4.8 eV) and ability to be easily doped n-type. Because the holes self-trap, the band-edge luminescence is weak; hence, β-Ga2O3 has not been regarded as a promising material for light emission. In this work, optical and structural imaging methods revealed the presence of localized surface defects that emit in the near-UV (3.27 eV, 380 nm) when excited by sub-bandgap light. The PL emission of these centers is extremely bright—50 times brighter than that of single-crystal ZnO, a direct-gap semiconductor that has been touted as an active material for UV devices.

Upconverted excitation energy lock-in for deep-ultraviolet enhancement

Photon upconversion of near-infrared (NIR) irradiation into deep-ultraviolet (UV) emission offers many exciting opportunities for drug release in deep tissues, photodynamic therapy, solid-state lasing, energy storage, and photocatalysis. However, NIR-to-deep-UV upconversion remains a daunting challenge due to low quantum efficiency. Here, we report an unusual six-photon upconversion process in Gd3+/Tm3+-codoped nanoparticles comprising a heterogeneous, core-multishell nanostructure. This multishell design efficiently suppresses energy consumption induced by interior energy traps, maximizes cascade sensitizations of the NIR excitation, and promotes upconverted deep-UV emission from high-lying excited states. We released the intense six-photon-upconverted UV emissions at 253 nm under 808-nm excitation. This work provides new insight into mechanistic understanding of the upconversion process within the heterogeneous architecture, while offering exciting opportunities for developing nanoscale deep-UV emitters that can be remotely controlled in deep tissues upon NIR illumination.