In this study, carbon dots (C-dots) were synthesized from resorcinol and trisodium phosphate in ethylene glycol using a microwave-assisted method. The C-dots exhibited predominantly green photoluminescence when excited at 460 nm. Their absorption and emission spectra showed strong solvent-dependent variations, and the quantum yield varied between 45% and 62% depending on the solvent. Both absorption and emission maxima exhibited a noticeable red shift with increasing solvent polarity. Upon varying the excitation wavelength from 300 to 480 nm, two distinct emission bands blue and green emerged. However, no continuous spectral shift was observed in any solvent. Excitation spectra recorded at different emission wavelengths also revealed two well-defined excitation peaks. The blue emission originates from π→π* transitions within the CC sp2 domains at the core of the C-dots, whereas the green emission arises from surface states associated with phenolic -OH and phosphate functional groups. The absence of continuous spectral shift in emission suggests the absence of heterogeneity in CC sp2 domains in the structure. The pH-dependent study revealed two emissive states: a dark state at acidic pH due to protonation of surface groups, and a highly emissive state at higher pH due to their deprotonation. Time-resolved photoluminescence showed specific solvent effects on the emission originating from core and surface of the C-dots. These findings establish that the green emission is strongly governed by the surface functional groups, while the core-related blue emission remains distinct.

The lead halide perovskite (LHP) nanocrystals (NCs) research area is flourishing due to their exceptional properties and great potential for a wide range of applications in optoelectronics and photovoltaics. Yet, despite the momentum in the field, perovskite devices are not yet ready for commercialization due to degradation caused by intrinsic phase transitions and external factors such as moisture, temperature, and ultraviolet (UV) light. To attain long-term stability, we analyze the origin of instabilities and describe different strategies such as surface modification, encapsulation, and doping for long-term viability. We also assess how these stabilizing strategies have been utilized to obtain optoelectronic devices with long-term stability. This Mini-Review also outlines the future direction of each strategy for producing highly efficient and ultrastable LHP NCs for sustainable applications.

The use of long-chain ligands in lead halide perovskite (LHP) nanocrystal (NC) synthesis impedes its charge transfer efficacy due to its insulating ligand environment. This report presents the first-ever in situ introduction of short-chain dicarboxylic acids instead of long-chain oleic acid for LHP NC synthesis to minimize the conductivity hindrance. As a template of a dicarboxylic acid, three-carbon-based malonic acid (MA) and ten-carbon-based sebacic acid (SA) have been used in the open-air hot injection process to synthesize highly luminescent LHP NCs covering the entire visible spectrum. MA's strong six-membered chelate passivation and superior surface coverage resulted in higher NC quality and higher PLQY for green-emitting CsPbBr3 NCs compared to the SA. In addition to NC synthesis, the formation of 2D layered perovskite nanoplates through the sebacate spacer anion as a side product of NCs has been discussed, which is unique and unprecedented. As a proof of concept, green down-converted LEDs have been fabricated by drop-casting short-chain acid-mediated CsPbBr3 NCs onto blue LEDs. The clear electroluminescence spectrum demonstrates its potential in display and lighting technologies, highlighting the promise of this synthetic approach for future device applications.

This report plies the effect of temperature on the interaction of GO and polyaniline at different pH through photoluminescence (PL) studies. At neutral pH, the interaction of GO-PANI is found to be highly temperature-dependent. A ground state charge transfer (CT) from the polaronic state of PANI to the GO remained at the backbone of the photophysics. The electron transfer from PANI to GO becomes more significant at a higher temperature because of the better interaction of GO with PANI moiety through π−π stacking and hydrogen bonding. The CT-induced PL amplification at elevated temperature is originating from the recombination of the spatially separated electron in the excited state of GO and hole in the PANI. The thermodynamic parameters ΔH and ΔS have been calculated associated with the electron transfer process. The positive change in the electronic entropy due to the better delocalization overcomes the entropy change due to structural orderness that drives the electron transfer process. The intensity of different PL bands remains unaffected by the temperature at lower pH due to saturated electron transfer and lower GO-PANI interaction, whereas at higher pH the CT PL band intensity decreases with an increment in temperature, explained by the increase in GO-PANI distance.

Cs3Cu2I5 perovskite displays a Stokes-shifted photoluminescence (PL) at 445 nm, attributed to the self-trapped excitons (STEs). Unlike that observed in other perovskite materials, the free-exciton emission is not evidenced in this case. Herein, we reveal the existence of a short-lived high-energy emission centered around 375 nm through the reconstruction of time-resolved emission spectra (TRES), which is independent of the shape/size of Cs3Cu2I5 perovskite. This high-energy emission is proposed to originate from the free-exciton-derived distorted S1 state of the 0D Cs3Cu2I5 moiety. Moreover, STE PL (∼445 nm) was found to have phosphorescence characteristics. Theoretical calculation confirms a facile intersystem crossing at the Franck-Condon geometry, indicating the high lifetime of the STE and its triplet nature. The existence of a high-energy emissive state and the phosphorescent nature of the STE PL band provide valuable insights that could advance our understanding of the photophysics in these materials.

To overcome organic solvent hazards, deep eutectic solvents have been employed for the synthesis of cesium lead halide perovskite nanocrystals/nanoplatelets.

Two-dimensional Ruddlesden-Popper(RP) lead halideperovskitenanoplates (NPls) have recently attracted attention due to their superiorproperties in optoelectronics. However, structural degradation ofthese materials under continuous photoexcitation restricts their acceptability.Herein, we report an instantaneous structural as well as optical recoveryof colloidal (OAm)(2)(CH3NH3PbI3)(2)PbI4 RP NPls from its UV-degradedstage through a simple "protonation" approach by proton-donatingspecies like 1-dodecanethiol, 4-aminothiophenol, and hydroiodic acid.

Solvent dependent photophysical properties of 6 -substituted N-methyl quinolone molecules namely 6-amino-1methylquinolin-2(1H)-one (AMQ), 1-methyl-6-(methylamino)quinolin-2(1H)-one (MAMQ), 1-methyl-6-nitroquinolin-2(1H)-one (NMQ) have been studied using steady state UV-Visible absorption, fluorescence emission spectroscopy, fluorescence lifetime measurements and quantum mechanical calculations. It was found that amine and methylamine substitution at 6-position of quinolone moiety enhanced the fluorescent property whereas nitro substitution rendered it non-fluorescent in all the experimental solvent systems. Maximum redshifted spectra were found in dimethyl sulfoxide (DMSO) compared to both alcoholic solvents and pure water. Significant charge transfer in HOMO to LUMO transition was revealed by quantum mechanical calculations but the direction was different depending on the nature of substitution. The pH response of the molecules were also investigated in pure water and the pKa values were found to be 3.70 and 3.90 for AMQ and MAMQ respectively. Analysis of radiative and non-radiative rate constants in all the solvents showed that the deactivation process may be different depending on hydrogen bond donation ability of the solvent. The spectral shift was rationalised by grouping the solvents based on their hydrogen bonding ability.

To investigate the interaction among the graphene oxide layers by involving surface functional groups, photoluminescence (PL) from graphene oxide (GO), and hydroxyl enriched graphene oxide (OH-GO) in the UV-visible region are studied. Tuning of PL is observed by varying the concentration of aqueous dispersion of OH-GO, obtained by strong alkaline treatment on graphene oxide (GO). FTIR, Raman, XRD, and the microscopic study suggests the structural orderness of the OH-GO compared to GO. Hydroxyl functional groups at the surface of OH-GO facilitate the formation of aggregates through hydrogen bonds by involving solvent water molecules and the PL band in the visible region may be originated from such aggregates. With the increase in the concentration of OH-GO in the aqueous medium, the contribution of the visible PL band is markedly increased along with the decrease in the PL band in the UV region. The time-resolved study indicates the possibility of energy transfer from the species emitting in the UV region to the species emitting in the visible region. This energy transfer may be responsible for the marked enhancement of the visible band of the PL spectra of OH-GO at high concentrations.

Fluorescent probes based on semiconducting polymer nanoparticles (NPs) such as polyaniline (PANI) usually require external fluorophore doping to provide fluorescence function. Direct use of PANI-based NPs for bioimaging applications has been limited by PANI's weak blue fluorescence and aggregation-induced quenching in physiological medium. In this report, we developed a facile solid-state synthesis method to produce fluorescent polyaniline nanoparticles (FPNs) that are not only water-soluble but also exhibit high intensity and pH-sensitive red fluorescence. The FPNs showed high photoluminescence quantum yield (PLQY) of 19.3 % at physiological pH, which makes FPNs ideal for application as fluorescent nanoprobes in bioimaging. Moreover, we performed an in-depth study of photoluminescence dependence on pH and the phenomena of exciton-polaron quenching at low pH was highlighted. We also found that the ratio of emission intensity at 600 nm and 650 nm increased from 0.04 to 1.65 as pH was raised from 2.6 to 11.8, which could find its application in ratiometric pH sensing. FPNs exhibited excellent biocompatibility with >85 % cell viability for fibroblasts NIH/3 T3 and prostate cancer 22RV1 cells even at concentrations as high as 1000 μg/mL. In addition, fluorescence microscopy demonstrated concentration-dependent red fluorescence in the cytoplasm owing to the cellular uptake of FPNs in prostate cancer cells.

Quantum-confined two-dimensional (2D) Ruddlesden-Pop-per (RP) perovskite nanoplates (NPls) are drawing considerable attention in recent times. The effect of external perturbations like air, moisture, heat, polarity of the solvent, and, specifically, light irradiation has significant impact on the RP perovskite structure in different ways. Though some reports are available on the effect of light irradiation on RP NPl single crystals, films, and flakes, no comprehensive study is available for the RP NPl colloidal state. To extend the understanding, we studied the fate of UV irradiation on a colloidal, orange-em itting oleylammonium iodide-based RP NPl, (C18H35NH3)2(CH3NH3PbI3)2PbI4 (n = 3). A constant UV exposure for 10 h transforms the RP NPl structure into a purely 3D methylammonium lead iodide (CH3NH3PbI3, MAPbI3) nanorod (NR) having a photo-luminescence quantum yield of 65%. Our experimental results reveal that this structural transformation takes place by ligand desorption, followed by structural association in an oriented fashion. The obtained MAPbI3 NR shows excellent optical and crystalline phase stability for more than 2 months.

Vulnerability to atmospheric conditions and their associated toxicity limit the practical/industrial use of perovskites despite their tremendous promise in optoelectronics.

Local environment dependent photoluminescence (PL) of cerium incorporated GO nanoparticles (GO-Ce NPs) is investigated by using fluorescence quenching study in presence of aromatic nitro compounds (ANCs) and fluoride ion. Presence of trivalent and tetravalent cerium ions at the different locations of the GO based nanoparticles interact with ANCs and fluoride ions in a different manner depending upon the accessibility and local polarity of the excited cerium (III) ions. Proposed system is found to be most sensitive towards ortho-nitrophenol (quenching efficiency 70.5 %) with a high constant value of K-D and K-S, 8.7 x 10(4) and 7.0 x 10(4) respectively. Herein, the fluorescence quenching study of GO-Ce NPS reveals the different mode of interactions between the fluorophoric moieties and quenchers.

In this article, we synthesized fluorescent nitrogen-enriched carbon nanoparticles (N-CNPs), which were prepared via the hydrothermal treatment of pyrolyzed seaweed extract and ethylene diamine at 160 degrees C for 12.0 h. These N-CNPs demonstrated a 12 nm average diameter with carbonyl, hydroxyl, and imine functionality on their surface. The zeta potential value was found to be negative which further confirms the presence of acid/imine groups on the surface of N-CNPs. The prepared N-CNPs showed strong blue fluorescence with 24% quantum yield under UV light illumination. Here, we introduced metal-free water dispersed N-CNPs as invisible ink for security purposes. The information was written by the N-CNPs in TLC plate and N-CNPs/PVA flexible composite film is invisible in daylight and can be readable in UV light illumination.

The low photoluminescence quantum yield of Bi3+-doped lead halide perovskite nanocrystals (NCs) is a big challenge to the scientific community. This makes them a weak candidate in the optoelectronics field in spite of their better stability than the pure lead analogue. Herein, the reason behind this reduction of quantum yield in hybrid mixed lead-bismuth bromide (MPBBr) NC is investigated and proposed to be due to ultrafast trapping transfer in the core of the NC, and not due to the surface trap states. Further, we have successfully boosted the quantum yield of MPBBr NC from 9% to 64% by passivating the deep traps within the crystal core by monovalent potassium ion doping. The stability of the developed Bi3+/K+-doped lead halide perovskite NC was found to be extremely high in atmospheric conditions, and this property is sustained up to 100 °C.

ABX3 perovskites offer the advantage of manipulating its properties by introducing multiple cations in B-site. Over the years, researchers used mixed B-site perovskites in oxide electronics to tune their electrical, magnetic properties. Here we used the triple cations at B-site in formamidinium based organometallic halide perovskite solar cell (PSC) in order to improve its degradation behavior with respect to heat and moisture. We synthesized halide based two hybrid perovskites viz., formamidinium sodium bismuth lead iodide [NH2CHNH2(Na0.25Bi0.25) Pb0.5I3] and formamidinium potassium bismuth lead iodide [NH2CHNH2(K0.25Bi0.25)Pb0.5I3] using solution chemistry. In order to decrease the content of toxic lead in these perovskites, trivalent bismuth was incorporated in the Pb-site. Monovalent sodium and potassium were used to maintain the charge neutrality of B-site, which has the formal valence of + 2 in these ABI3 type perovskites. Both of these perovskites showed reasonable optical band gaps with good charge carrier lifetime suggesting it as potential candidates for solar energy conversion and provisionally we achieved power conversion efficiency eta = 0.52%. Moreover, superior thermal and moisture stability in these perovskites were observed in periodical structural and spectral analysis carried out by XRD, UV-Vis spectroscopy, time-correlated single photon counting (TCSPC) over the period of one month. Furthermore, ultrafast carrier dynamics in these perovskites were unraveled using femtosecond transient absorption studies. Our transient absorption kinetics data suggested more auger recombination and faster free electron-hole recombination process in FKBPI compared to FNBPI, which corroborates well with better energy conversion efficiency obtained in FNBPI based solar cell.

This work demonstrates a strategy to overcome the limitation of weakly luminescent graphene oxide (GO) based materials by using a simple one pot synthesis of enormously luminescent cerium ion incorporated graphene oxide nanoparticles (GO-Ce NPs). Apart from more than 100 fold amplification of photoluminescence intensity compared to graphene oxide, the origin of such enhancement of GO-Ce NPs is investigated by exploring binding interaction between cerium ions and GO NPs and the structural orderness of the GO NPs in presence of cerium. XPS confirms the existence of two oxidation states of cerium in GO-Ce NPs. Experimental observations enable us to conclude a mechanism involving photoinduced reduction of non emissive Ce (IV) to form luminescent Ce (III) accompanied with energy pumping of cerium by photoexcited GO NPs in the structurally ordered GO-Ce nanoparticles. Again, the interaction between the cerium ions and the oxygen containing functional groups of GO leads to decoupling of the functional groups and there by weakens the intensity of luminescence originated from disordered induced defect states which results a non radiative chanel to generate trivalent cerium via single electron transfer from the orbitals of the functional groups to the vacant 4f orbitals of tetravalent cerium.

In this study, we report a controlled one-pot green synthesis of multiwalled carbon nanotubes (MWCNTs) via pyrolysis of sustainable agriculture waste (chickpea peel) at 400 °C in aqueous medium. These MWCNTs demonstrated 7.0 nm diameter, 0.28 nm graphitic spacing with carbonyl, hydroxyl, and carboxylic acid functionality. The D band (presence of sp3 defects) and G band (E2g mode of graphite) at 1350 cm−1 and 1580 cm−1 originated in Raman spectrum, respectively. The prepared MWCNTs showed blue fluorescence with 10% fluorescence quantum yield in aqueous medium. The MWCNTs showed triple exponential decay characteristics with an average fluorescence lifetime of 4.7 ns. The synthesized MWCNTs revealed a consistent fluorescence in the cytoplasm of 22RV1 human prostate carcinoma cell line without exerting any sign of cytotoxicity. The MWCNTs also exhibited remarkable cytocompatibility in human immortalized prostate epithelial RWPE1 cells.

An ultra-slow crystal growth over a period of 24 h of a newly synthesized CH3NH3Pb1/2Bi1/3I3 perovskite (MPBI) nanocrystal in non-polar toluene medium is reported here. From several spectroscopic techniques as well as from TEM analysis we found that the size of nanocrystals changes continuously with time, in spite of being capped by the ligands. Using a single molecular spectroscopic technique, we also found that this size change is not due to the stacking of nanocrystals but due to crystal growth. The notable temperature dependence and reversible nature of the nanocrystals growth is explained by the dynamic nature of the capping. The observed temperature-dependent ultra-slow growth is believed to be a pragmatic step towards controlling the size of perovskite NC in a systematic manner.

This work describes the design and synthesis of fluorescent triphenylamine-thiazolothiazole based donor-acceptor-donor chemosensor 4,4 '-(thiazolo[5,4-d]thiazole-2,5-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TTz-1). TTz-1 exhibited positive solvatochromism effect in the excited state due to its strong intramolecular charge transfer (ICT) properties. Potential application of TTz-1 toward metal ion detection were explored systematically. It was established that the addition of Cu(ClO4)(2) (.) 6H(2)O into TTz-1 resulted in near-infrared (NIR) colorimetric and fluorescent quenching allowing for Cu2+ detection. EPR studies indicate that formation of radical cation occurs when Cu2+ and TTz-1 interact. TTz-1 was also able to detect Fe3+ employing a color change from orange to colourless (fluorescent). It was observed that the TTz-1 emission peak at 567 nm was quenched after addition of Cu2+ and Fe3+ metal ions. Electrochemical analysis showed that LUMO values of the TTz-1 decreased after addition of Fe3+ and Cu2+. The limits of detection (LOD) for Cu2+ and Fe3+ detection by TTz-1 were found to be 0.30 mu M and 0.29 mu M, respectively. These results suggest that the TTz-1 is a highly selective and sensitive sensor for the detection of Cu2+ or Fe3+ ions.