Enhanced Emission from WSe2 Monolayers Coupled to Circular Bragg Gratings

Two-dimensional transition-metal dichalcogenides (TMDC) are of great interest for on-chip nanophotonics due to their unique optoelectronic properties. Here, we propose and realize coupling of tungsten diselenide (WSe2) monolayers to circular Bragg grating structures to achieve enhanced emission. The interaction between WSe2 and the resonant mode of the structure results in Purcell-enhanced emission, while the symmetric geometrical structure improves the directionality of the out-coupling stream of emitted photons. Furthermore, this hybrid structure produces a record high contrast of the spin valley readout (> 40%) revealed by the polarization resolved photoluminescence (PL) measurements. Our results are promising for on-chip integration of TMDC monolayers with optical resonators for nanophotonic circuits

The Influence of the Environment and Clothing on Human Exposure to Ultraviolet Light

<div><p>Objection</p><p>The aim of this study is to determine the effect of clothing and the environment on human exposure to ultraviolet light.</p><p>Methods</p><p>The ultraviolet (ultraviolet A and ultraviolet B) light intensity was measured, and air quality parameters were recorded in 2014 in Beijing, China. Three types of clothing (white polyester cloth, pure cotton white T-shirt, and pure cotton black T-shirt) were individually placed on a mannequin. The ultraviolet (ultraviolet A and ultraviolet B) light intensities were measured above and beneath each article of clothing, and the percentage of ultraviolet light transmission through the clothing was calculated.</p><p>Results</p><p>(1) The ultraviolet light transmission was significantly higher through white cloth than through black cloth; the transmission was significantly higher through polyester cloth than through cotton. (2) The weather significantly influenced ultraviolet light transmission through white polyester cloth; transmission was highest on clear days and lowest on overcast days (ultraviolet A: <i>P</i>=0.000; ultraviolet B: <i>P</i>=0.008). (3) Air quality parameters (air quality index and particulate matter 2.5 and 10) were inversely related to the ultraviolet light intensity that reached the earth’s surface. Ultraviolet B transmission through white polyester cloth was greater under conditions of low air pollution compared with high air pollution.</p><p>Conclusion</p><p>Clothing color and material and different types of weather affected ultraviolet light transmission; for one particular cloth, the transmission decreased with increasing air pollution.</p></div

UVA transmission through white polyester with different levels of air pollution.

<p>The data on the Y-axis begin at 32%. * The air quality was divided into five levels based on the AQI: 1: 0–50, good; 2: 51–100, moderate; 3:101–150, unhealthy for sensitive groups; 4: 151–200, unhealthy; 5: 201–300, very unhealthy. UVA transmission in the presence of air quality levels 1, 2, and 3 was significantly different from that for levels 4 and 5.</p

The relationship between environmental relative humidity and temperature and UVA transmission through white polyester.

<p>A: Pearson’s correlation analysis revealed a significant negative correlation between relative humidity and UVA transmission through white polyester (r = -0.4774, <i>P</i><0.0001). B: Pearson’s correlation analysis showed a significant positive correlation between temperature and UVA transmission through white polyester (r = 0.3888, <i>P</i><0.0001).</p

Ultraviolet light transmission through different types of clothing (%).

<p>WP, White Polyester; WC, White Cotton; BC, Black Cotton. WP1cm and WC1cm indicate that the distance between the clothing and the skin was 1 centimeter. * The transmission through this type of clothing was significantly different (<i>P</i><0.05) from that through WC. # The transmission through WP was significantly different (<i>P</i><0.05) from that through WP1cm.</p

Changes in ultraviolet light intensity at different times and in three types of weather.

<p>Regardless of the weather, the UVA and UVB intensities were highest at 12:00 each day. There were significant differences in the UVA intensity among the three types of weather; the UVA and UVB intensities peaked on clear days and were lowest on overcast days.</p

Ultraviolet light intensity at different anatomical sites.

<p>Although the back and the left elbow showed no significant differences in exposure to ultraviolet light, there were significant differences in the UVA and UVB intensities experienced at the four anatomical sites.</p

Ultraviolet intensity in 5 air quality grades.

<p>* The air quality was divided into five grades based on the AQI: grade 1, 0–50, Excellent; grade 2, 51–100, Good; grade 3, 101–150, Mild Pollution; grade 4, 151–200, Moderate Pollution; grade 5, 201–300, Serious Pollution. As air pollution increased, the ultraviolet intensity decreased.</p

Ultraviolet light intensity at different times in three types of weather (μW/cm²).

<p>Ultraviolet light intensity at different times in three types of weather (μW/cm²).</p

Changes in ultraviolet light intensity and air quality on all the experimental days.

<p>※ clear day, # cloudy, and & overcast. * The UVA and UVB data are presented in μW/cm² and 10×μW/cm², respectively.</p