Slow Auger Recombination in Ag2Se Colloidal Quantum Dots.

Efficient Auger recombination (AR) presents a significant challenge for the advancement of colloidal quantum dot (QD)-based devices involving multiexcitons. Here, the AR dynamics of near-infrared Ag2Se QDs were studied through transient absorption experiments. As the QD radius increases from 0.9 to 2.5 nm, the biexciton lifetime (τ2) of Ag2Se QDs increases from 35 to 736 ps, which is approximately 10 times longer than that of comparable-sized CdSe and PbSe QDs. A qualitative analysis based on observables indicates that the slow Auger rate is primarily attributed to the low density of the final states. The biexciton lifetime and triexciton lifetime (τ3) of Ag2Se QDs follow R3 and R2.6 dependence, respectively. Moreover, the ratio of τ2/τ3 is ∼2.3-3.2, which is markedly lower than the value expected from statistical scaling (4.5). These findings suggest that environmentally friendly Ag2Se QDs can serve as excellent candidates for low-threshold lasers and third-generation photovoltaics utilizing carrier multiplication.

Feasibility assessment: application of ecological floating beds for polluted tidal river remediation.

The remediation of polluted coastal rivers is a global challenge in the environmental field. The objective of this study was to investigate the remediation feasibility of a high-salinity river using water spinach (WS) and sticky rice (SR) in hydroponic floating-bed systems. In this study, the total nitrogen (TN) removal rates were 89.7, 92.3, 85.1, and 75.2% in the WS floating-bed system and 81.2 and 78.9% in the SR floating-bed system under different salinities (2-31 psu). Additionally, the total phosphorus (TP) removal rates were 94.4, 96.4, 93.5, and 75.2% in the WS floating-bed system and 75.7 and 80.0% in the SR floating-bed system under different salinities. The results indicate that WS and SR significantly contributed to the remediation of a polluted tidal river. Additionally, increased salinity suppressed the removal of ammonium and phosphate by WS and SR. The salt tolerance of WS was greater than that of SR, which indicated that WS was a more appropriate choice for treating river contamination.

Toward temperature-insensitive near-infrared optical gain using low-toxicity Ag2Se quantum dots.

With the growing demand for developing lasers with high stability and integration, temperature-insensitive gain materials are highly desirable. Here, temperature-insensitive near-infrared (NIR) optical gain from low-toxicity Ag2Se quantum dots (QDs) is reported. Due to the large energy splitting between the band-edge hole state and the following state (∼430 meV), the thermal depopulation of the band-edge hole state in Ag2Se QDs is significantly suppressed. The long biexciton lifetime (245 ps at 300 K) of the QDs is sufficient to support the establishment of amplified spontaneous emission (ASE). Consequently, the characteristic temperature of the ASE threshold for the Ag2Se QD film is as high as 360 K, and efficient NIR ASE is observed up to 340 K. In addition, when the temperature is lower than 200 K, the ASE peak position is temperature insensitive because acoustic phonons cannot be effectively excited. Our findings reveal that Ag2Se QDs can be utilized as an excellent gain material for environmentally friendly temperature-insensitive NIR lasers.