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1. Effect of nanoscale dielectric environments on concentration quenching

   https://doi.org/10.1515/nanoph-2021-0132  

   Rout, Sangeeta ; Koutsares, Samantha R. ; Courtwright, Devon ; Mills, Ezekiel ; Shorter, Ayanna ; Prayakarao, Srujana ; Bonner, Carl E. ; Noginov, Mikhail A. ( August 2021 , Nanophotonics)

   Abstract We have studied the dependence of concentration quenching of luminescence (donor–acceptor energy transfer) on the thickness d of dye-doped polymeric films (HITC:PMMA) and found its strong inhibition at small values of d . This phenomenon is tentatively explained by a limited number of acceptors, which donors’ excitation can reach in thin samples, if the film’s thickness is comparable to the diffusion length of the energy transfer. The latter mechanism, along with effective reduction of the dye concentration, is responsible for an inhibition of the concentration quenching of dye molecules impregnating porous alumina membranes. The elongation of emission kinetics in thick (≥3 μm) HITC:PMMA films is cautiously attributed to the samples’ crystallinity.
2. Exploring the optical properties of La ₂ Hf ₂ O ₇ :Pr ³⁺ nanoparticles under UV and X-ray excitation for potential lighting and scintillating applications

   https://doi.org/10.1039/c8nj00895g  

   Zuniga, Jose P. ; Gupta, Santosh K. ; Pokhrel, Madhab ; Mao, Yuanbing ( January 2018 , New Journal of Chemistry)

   New optical materials with efficient luminescence and scintillation properties have drawn a great deal of attention due to the demand for optoelectronic devices and medical theranostics. Their nanomaterials are expected to reduce the cost while incrementing the efficiency for potential lighting and scintillator applications. In this study, we have developed praseodymium-doped lanthanum hafnate (La 2 Hf 2 O 7 :Pr 3+ ) pyrochlore nanoparticles (NPs) using a combined co-precipitation and relatively low-temperature molten salt synthesis procedure. XRD and Raman investigations confirmed ordered pyrochlore phase for the as-synthesized undoped and Pr 3+ -doped La 2 Hf 2 O 7 NPs. The emission profile displayed the involvement of both the 3 P 0 and 1 D 2 states in the photoluminescence process, however, the intensity of the emission from the 1 D 2 states was found to be higher than that from the 3 P 0 states. This can have a huge implication on the design of novel red phosphors for possible application in solid-state lighting. As a function of the Pr 3+ concentration, we found that the 0.1%Pr 3+ doped La 2 Hf 2 O 7 NPs possessed the strongest emission intensity with a quantum yield of 20.54 ± 0.1%. Themore »concentration quenching, in this case, is mainly induced by the cross-relaxation process 3 P 0 + 3 H 4 → 1 D 2 + 3 H 6 . Emission kinetics studies showed that the fast decaying species arise because of the Pr 3+ ions occupying the Hf 4+ sites, whereas the slow decaying species can be attributed to the Pr 3+ ions occupying the La 3+ sites in the pyrochlore structure of La 2 Hf 2 O 7 . X-ray excited luminescence (XEL) showed a strong red-light emission, which showed that the material is a promising scintillator for radiation detection. In addition, the photon counts were found to be much higher when the NPs are exposed to X-rays when compared to ultraviolet light. Altogether, these La 2 Hf 2 O 7 :Pr 3+ NPs have great potential as a good down-conversion phosphor as well as scintillator material.« less
3. Effect of Random Nanostructured Metallic Environments on Spontaneous Emission of HITC Dye

   https://doi.org/10.3390/nano10112135  

   Rout, Sangeeta ; Qi, Zhen ; Petrosyan, Ludvig S. ; Shahbazyan, Tigran V. ; Biener, Monika M. ; Bonner, Carl E. ; Noginov, Mikhail A. ( November 2020 , Nanomaterials)

   We have studied emission kinetics of HITC laser dye on top of glass, smooth Au films, and randomly structured porous Au nanofoams. The observed concentration quenching of luminescence of highly concentrated dye on top of glass (energy transfer to acceptors) and the inhibition of the concentration quenching in vicinity of smooth Au films were in accord with our recent findings. Intriguingly, the emission kinetics recorded in different local spots of the Au nanofoam samples had a spread of the decay rates, which was large at low dye concentrations and became narrower with increase of the dye concentration. We infer that in different subvolumes of Au nanofoams, HITC molecules are coupled to the nanofoams weaker or stronger. The inhibition of the concentration quenching in Au nanofoams was stronger than on top of smooth Au films. This was true for all weakly and strongly coupled subvolumes contributing to the spread of the emission kinetics. The experimental observations were explained using theoretical model accounting for change in the Förster radius caused by the strong energy transfer to metal.
4. The SAMI Galaxy Survey: the role of disc fading and progenitor bias in kinematic transitions

   https://doi.org/10.1093/mnras/stab1494  

   Croom, S M ; Taranu, D S ; van de Sande, J ; Lagos, C D ; Harborne, K E ; Bland-Hawthorn, J ; Brough, S ; Bryant, J J ; Cortese, L ; Foster, C ; et al ( June 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We use comparisons between the Sydney-AAO Multi-object Integral Field Spectrograph (SAMI) Galaxy Survey and equilibrium galaxy models to infer the importance of disc fading in the transition of spirals into lenticular (S0) galaxies. The local S0 population has both higher photometric concentration and lower stellar spin than spiral galaxies of comparable mass and we test whether this separation can be accounted for by passive aging alone. We construct a suite of dynamically self-consistent galaxy models, with a bulge, disc, and halo using the galactics code. The dispersion-dominated bulge is given a uniformly old stellar population, while the disc is given a current star formation rate putting it on the main sequence, followed by sudden instantaneous quenching. We then generate mock observables (r-band images, stellar velocity, and dispersion maps) as a function of time since quenching for a range of bulge/total (B/T) mass ratios. The disc fading leads to a decline in measured spin as the bulge contribution becomes more dominant, and also leads to increased concentration. However, the quantitative changes observed after 5 Gyr of disc fading cannot account for all of the observed difference. We see similar results if we instead subdivide our SAMI Galaxy Survey sample by starmore »formation (relative to the main sequence). We use EAGLE simulations to also take into account progenitor bias, using size evolution to infer quenching time. The EAGLE simulations suggest that the progenitors of current passive galaxies typically have slightly higher spin than present day star-forming disc galaxies of the same mass. As a result, progenitor bias moves the data further from the disc fading model scenario, implying that intrinsic dynamical evolution must be important in the transition from star-forming discs to passive discs.« less
5. Influence of dissolved organic matter on carbonyl sulfide and carbon disulfide formation from cysteine during sunlight photolysis

   https://doi.org/10.1039/D0EM00219D  

   Modiri Gharehveran, Mahsa ; Hain, Ethan ; Blaney, Lee ; Shah, Amisha D. ( September 2020 , Environmental Science: Processes & Impacts)

   Carbonyl sulfide (COS) and carbon disulfide (CS 2 ) are important atmospheric gases that are formed from organic sulfur precursors present in natural waters when exposed to sunlight. However, it remains unclear how specific water constituents, such as dissolved organic matter (DOM), affect COS and CS 2 formation. To better understand the role of DOM, irradiation experiments were conducted in O 2 -free synthetic waters containing four different DOM isolates, acquired from freshwater to open ocean sources, and the sulfur-based amino acid, cysteine (CYS). CYS is a known natural precursor of COS and CS 2 . Results indicated that COS formation did not vary strongly with DOM type, although small impacts were observed on the kinetic patterns. COS formation also increased with increasing CYS concentration but decreased with increasing DOM concentration. Quenching experiments indicated that ˙OH was not involved in the rate-limiting step of COS formation, whereas excited triplet states of DOM ( 3 CDOM*) were plausibly involved, although the quenching agents used to remove 3 CDOM* may have reacted with the CYS-derived intermediates as well. CS 2 was not formed under any of the experimental conditions. Overall, DOM-containing synthetic waters had a limited to no effect towards forming COSmore »and CS 2 , especially when compared to the higher concentrations formed in sunlit natural waters, as examined previously. The reasons behind this limited effect need to be explored further but may be due to the additional water quality constituents present in these natural waters. The findings of this study imply that multiple variables beyond DOM govern COS and CS 2 photoproduction when moving from freshwaters to open ocean waters.« less