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Single particle level microscopy of immobilized FAPbBr3 nanocrystals (NCs) has elucidated the involvement of different processes in their photoluminescence (PL) intermittency. Four different blinking patterns are observed in the data from more than 100 NCs. The dependence of PL decays on PL intensities brought out in fluorescence lifetime intensity distribution (FLID) plots is rationalized by the interplay of exciton- and trion-mediated recombinations along with hot carrier (HC) trapping. The high intensity-long lifetime component is attributed to neutral exciton recombination, the low intensity-short lifetime component is attributed to trion assisted recombination, and the low intensity-long lifetime component is attributed to hot carrier recombination. Change-point analysis (CPA) of the PL blinking data reveals the involvement of multiple intermediate states. Truncated power law distribution is found to be more appropriate than power law and lognormal distribution for on and off events. Probability distributions of PL trajectories of single NCs are obtained for two different excitation fluences and wavelengths (λex = 400, 440 nm). Trapping rate (kT) prevails at higher power densities for both excitation wavelengths. From a careful analysis of the FLID and probability distributions, it is concluded that there is competition between the HC and trion assisted blinking pathways and that the contribution of these mechanisms varies with excitation wavelength as well as fluence. [ABSTRACT FROM AUTHOR]

The doping of CdS quantum dots (QDs) with Cu(I) disrupts electron–hole correlation due to hole trapping by the dopant ion, post-photoexcitation. The present paper examines the effect of such disruption on the rate of photoinduced electron transfer (PET) from the QDs to methyl viologen (MV2+), with implications in their photocatalytic activity. A significantly greater efficiency of PL quenching by MV2+ is observed for the doped QDs than for the undoped ones. Interestingly, the Stern–Volmer plots constructed using PL intensities exhibit an upward curvature for both the cases, while the PL lifetimes remain unaffected. This observation is rationalized by considering the adsorption of the quencher on the surface of the QDs and ultrafast PET post-photoexcitation. Ultrafast transient absorption experiments confirm a faster electron transfer for the doped QDs. It is also realized that the transient absorption experiment yields a more accurate estimate of the binding constant of the quencher with the QDs, than the PL experiment. [ABSTRACT FROM AUTHOR]

The electrical and optoelectrical characteristics of graphene oxide thin film have been studied to establish its potential for various device applications. Symmetric nonlinear hysteresis in a current–voltage space, a typical memristor characteristic, has been observed using a planar metal/insulator/metal configuration. The obtained current–voltage behavior of the device has been visualized based on the voltage-dependent contributions from various charge carriers in the presence of different trap sites in the fabricated thin film. The uniqueness of this device's characteristics is to show a bias voltage-dependent polarity switching of photoresponse under illumination, and this photoswitching occurs through a switching voltage point (∼2 V). The time dynamics of this photocurrent reveal that under a low bias voltage (<2 V), the device shows capacitive memristor characteristics. The exponentially growing photocurrent is additive in nature, and the device shows the photoresponse having a time constant of ∼2 s at +1 V. As bias voltage increases (>2 V), another current appears opposite to the normal photocurrent that depends on the bias voltage and intensity of illumination. A detailed analysis of the time dynamics of photoresponse reveals that the time constant of this current changes from ∼9 s (+2 V) to ∼5 s (+4 V). The observed photoswitching is due to different time constants of these counter-interacting currents, resulting in polarity switching. Here, we attempt to shed light on the fundamental mechanisms that connect the nonlinear, nonzero crossing hysteresis observed in the electrical characteristics with its voltage-dependent photoswitching that can be judicially exploited for conceptualizing graphene oxide-based photonic devices. [ABSTRACT FROM AUTHOR]

Here we report a facile method of functionalization of single-walled carbon nanotubes (SWNTs) with polypyrrole and making a chemiresistive sensor using the functionalized nanomaterial for sub-part-per-million detection of ammonia gas at room temperature. The sensor fabrication involves three steps: (i) immobilization of SWNTs by dip coating method on a silane-treated silicon/silicon dioxide substrate, (ii) printing of two parallel lines of conducting silver paste 5 mm apart as source and drain to define the source and the drain electrode, and (iii) in-situ electrochemical polymerization to functionalize the SWNTs with polypyrrole. The functionalization of SWNT was confirmed using electrochemical current-voltage measurements. The functionalized SWNTs exhibited several folds higher sensitivity to ammonia gas than the pristine SWNTs. A charge density of 0.85 C.cm−2 was optimum for electrochemical functionalization, providing maximum sensing response toward ammonia. The functionalized SWNTs showed a large measurable response starting from 50 to 750 part-per-billion (ppb) of ammonia with a sensitivity of ∼1.55% per ppb, and a limit of detection of 5 ppb of ammonia. Almost complete recovery of the sensor and an average response time of ∼9 min was also observed. [ABSTRACT FROM AUTHOR]

Light emission from organoboron compounds of Schiff bases is found to depend strongly on their chemical structure. Two of these compounds (OB1 and OB2), which contain a benzene ring between the Schiff base moieties, exhibit weak fluorescence in methanol, with marked viscosity dependence. Fluorescence lifetimes of these compounds are in picosecond timescale, as determined by femtosecond optical gating (FOG). A significant enhancement in fluorescence intensity and lifetime is observed at 77 K, indicating the operation of an activated nonradiative process. Using fluorescence lifetime imaging microscopy (FLIM), OB1 and OB2 are shown to be potential membrane probes. The third (OB3), which is devoid of this benzene ring, exhibits relatively stronger fluorescence with nanosecond lifetimes at room temperature. No viscosity dependence is observed in this case. The emission spectrum at 77 K is markedly more intense and exhibits an additional red shifted structured feature, which persists for a few seconds. Hence, OB3 seems to have greater promise not only as fluorescent probe but also for light harvesting. The marked improvement of the light emission properties of OB3 compared with OB1 and OB2 is likely to serve as a pointer for the design of Schiff base‐derived organoboron luminophores with diverse potential applications. [ABSTRACT FROM AUTHOR]