PL Measurements Research Articles

Post-synthetically covalent modification of g-C3N4 to regulate electronic structure and investigation of photocatalytic activity for eliminating antibiotics

Antibiotic residues in water have induced serious environment issues, and semiconductor photocatalysis has been proved as an effective technology for antibiotic elimination. Herein, a post-synthetic strategy was employed to covalently modify g-C3N4 (GCN) with methoxybenzoyl (MOB) via amido bond formation between the terminal amino of GCN and the p-anisoyl chloride. SEM and XRD characterizations indicated the morphologic and structural preservation after MOB modification, and FTIR and XPS results suggested the successful modification of MOB onto the GCN skeleton. Through effectively decreasing the electron cloud density of framework by the amido formation and the grafted MOB, the separation and migration of photogenerated charges were promoted, which were verified by PL and electrochemical measurements. As a result, the MOB/GCN showed greatly improved visible-light-driven photocatalytic activity for MOX degradation compared to the pristine GCN. Reaction parameters, such as synthetic temperature, pH value, photocatalyst dosage and MOX concentration were optimized, and the good photocatalytic durability and applicability in real scenarios were also demonstrated. Finally, the degradation pathway of MOX and the possible mechanism to explain the enhanced photocatalytic performance were proposed. This work demonstrates that covalent modification via the post-synthetic route is a promising approach to meliorate the photocatalytic behavior of GCN.

Inverting electrodeposited nanostructured Cu2O thin films from n-type to p-type semiconductors and variation of their physical and photoelectrochemical properties for optoelectronic applications

Employing identical techniques to produce the semiconductor with n and p-type conductivity is one of the most important keys to fabricating higher performance optoelectronic devices. Therefore, here the electrodeposition technique was employed to grow nanostructured Cu2O thin films with different pH values ranging from 3.5 to 13 from the same precursors before starting the deposition process. The morphological, structural, optical, electrical, and photoelectrochemical properties of fabricated Cu2O thin films were investigated employing SEM, EDX, XRD, Raman, UV–Vis, PL, Photocurrent, Mott-Schottky, and electrochemical impedance spectroscopy (EIS) measurements. XRD results showed the formation of Cu, Cu2O, and CuO phases with low pH values, while only Cu2O phase is obtained with higher pH. Raman measurements proven phonon modes of nanostructured Cu2O thin films. The morphology varies with different shapes such as spherical, pyramids, and prisms according to pH values. The optical absorption edge has appeared between 475 nm and 575 nm which indicates the formation of Cu2O and the calculated band gap varies from 2 to 2.44 eV. PL measurements indicate two dominant peaks related to inter-band transitions and defects including copper interstitials. Photocurrent measurements denoted that samples with lower pH from 6 to 7.6 are n-type semiconductors, while higher ones from 8 to 13 are p-type semiconductors. Mott-Schottky measurements showed that the donor’s density declines from about 2 × 1017 cm− 3 to about 1.6 × 1016 cm− 3 as pH increases from 6 to 7.6 whereas the acceptor’s density rises from about 1.25 × 1017 cm− 3 to about 3 × 1018 cm− 3 as pH increases from 8 to 13. EIS results show that both p-type and n-type samples have higher separation and transfer of charge carriers. Our outcomes indicate that the electrodeposited nanostructured Cu2O thin films are appropriate materials for biosensors, solar cells, and supercapacitors applications.

Distinct Optical and Structural (Nanoyarn and Nanomat-like Structure) Characteristics of Zinc Oxide Nanofilm Derived by Using Salvia officinalis Leaves Extract Made without and with PEO Polymer

This paper reports the optical properties of zinc oxide nanofilm fabricated by using organic natural products from Salvia officinalis leaves (SOL) extract and discusses the effect of the nanocrystal (NC) structure (nanoyarn and nanomat-like structure) on nanofilm optical properties. The surface-active layer of the nanofilm of ZnO nanoparticles (ZnO NPs) was passivated with natural organic SOL leaves hydrothermally, then accumulated on zinc oxide nanorods (ZnO NRs). The nanofilms were fabricated (with and without PEO) on glass substrate (at 85 °C for 16 h) via chemical solution deposition (CSD). The samples were characterized by UV-vis, PL, FESEM, XRD, and TEM measurements. TEM micrographs confirmed the nucleation of ZnO NPs around 4 nm and the size distribution at 1.2 nm of ZnO QDs as an influence of the quantum confinement effect (QCE). The nanofilms fabricated with SOL surfactant (which works as a capping agent for ZnO NPs) represent distinct optoelectronic properties when compared to bulk ZnO. FESEM images of the nanofilms revealed nanoyarn and nanomat-like structures resembling morphologies. The XRD patterns of the samples exhibited the existence of ZnO nanocrystallites (ZnO NCs) with (100), (002), and (101) growth planes. The nanofilms fabricated represented a distinct optical property through absorption and broad emission, as the optical energy band gap reduced as the nanofilms annealed (at 120 ℃). Based on the obtained results, it was established that phytochemicals extracted from organic natural SOL leaves have a distinct influence on zoic oxide nanofilm fabrication, which may be useful for visible light spectrum trapping. The nanofilms can be used in photovoltaic solar cell applications.

Photocatalytic degradation of ciprofloxacin using semiconductor derived from heterostructured ZIF-8-based materials

The combination of zeolitic imidazolates framework (ZIF) with porous solids with an analogous structure may represent a new class of heterostructured materials with improved properties for application in advanced oxidative processes. In this work, the in situ synthesis of ZIF-8 was carried out in the presence of the sodalite zeolite (SOD) to obtain the heterostructured ZIF-8/SOD. The thermal treatment of the previously formed heterostructure made it possible to obtain a surface enriched with ZnO from the ZIF-8 fraction, with the formation of the ZnO/SOD heterostructure. The formation of ZIF-8 and its derivative ZnO in sodalite was confirmed using different physicochemical techniques, such as PXRD, FTIR, 13C, 27Al and 29Si NMR, SEM, EDS, DRS-UV, TOC, PL, EIS and photocurrent measurements. Specific surface and porosity studies revealed that both heterostructures are composed of a wide range of pore sizes and distributions. Such materials were used as photocatalysts in the degradation of ciprofloxacin antibiotic drug. The ZIF-8/SOD heterostructure showed good photocatalytic capacity; however, superior performance was revealed for that thermally treated material, showing a degradation rate of approximately 98% in 120 min of the assay. Besides pH studies, PL and electrochemical assays indicated the efficient charge separation, while tests to inhibit the reactive species in the photocatalytic process suggested that the contaminant removal process involved a combined effect of both adsorption and photocatalysis, where the superoxide radical is the main specie responsible for the degradation of ciprofloxacin.

Strongly luminescent and highly stable CsPbBr3/Cs4PbBr6 core/shell nanocrystals and their ultrafast carrier dynamics

All-inorganic lead halide perovskites nanocrystals (NCs) have been demonstrated to be promising candidates for optoelectronic devices, but preparing perovskite NCs with high photoluminescence quantum yields (PLQYs) and excellent stability has been a challenge. In this work, CsPbBr3/Cs4PbBr6 core/shell NCs with a PLQYs of 87.23% and long-term stability in ambient environments was prepared by room temperature inverse microemulsion method. The excellent stability of the sample was attributed to the protection of Cs4PbBr6, and higher PLQYs could be owing to the passivation effect of the core/shell structure. To illustrate the distribution of photogenerated carrier in the core/shell structure, a confined excitons model was proposed based on time-resolved PL and temperature dependent PL measurements. Femtosecond time-resolved transient absorption spectra measurements were performed upon different excitation wavelength to unveil the photogenerated carrier dynamics in core/shell NCs. Upon 300 nm excitation, a carrier transfer process with the time of 3.18 ps from shell to core layer was observed. Furthermore, both two- and three-photon absorption PL was discovered in core/shell NCs, further verifying the carrier transfer process.

Advancement of Physical and Photoelectrochemical Properties of Nanostructured CdS Thin Films toward Optoelectronic Applications.

CdS thin films were grown on an FTO substrate at different temperatures, employing the low-cost hydrothermal method. All the fabricated CdS thin films were studied using XRD, Raman spectroscopy, SEM, PL spectroscopy, a UV-Vis spectrophotometer, photocurrent, Electrochemical Impedance Spectroscopy (EIS), and Mott-Schottky measurements. According to the XRD results, all the CdS thin films were formed in a cubic (zinc blende) structure with a favorable (111) orientation at various temperatures. The Scherrer equation was used to determine the crystal size of the CdS thin films, which varied from 25 to 40 nm. The SEM results indicated that the morphology of thin films seems to be dense, uniform, and tightly attached to the substrates. PL measurements showed the typical green and red emission peaks of CdS films at 520 nm and 705 nm, and these are attributable to free-carrier recombination and sulfur vacancies or cadmium vacancies, respectively. The optical absorption edge of the thin films was positioned between 500 and 517 nm which related to the CdS band gap. For the fabricated thin films, the estimated Eg was found to be between 2.50 and 2.39 eV. According to the photocurrent measurements, the CdS thin films grown were n-type semiconductors. As indicated by EIS, resistivity to charge transfer (RCT) decreased with temperature, reaching its lowest level at 250 °C. Flat band potential and donor density were found to fluctuate with temperature, from 0.39 to 0.76 V and 4.41 × 1018 to 15.86 × 1018 cm-3, respectively, according to Mott-Schottky measurements. Our results indicate that CdS thin films are promising candidates for optoelectronic applications.

Large area MoS2 thin film growth by direct sulfurization

In this study, we present the growth of monolayer MoS2 (molybdenum disulfide) film. Mo (molybdenum) film was formed on a sapphire substrate through e-beam evaporation, and triangular MoS2 film was grown by direct sulfurization. First, the growth of MoS2 was observed under an optical microscope. The number of MoS2 layers was analyzed by Raman spectrum, atomic force microscope (AFM), and photoluminescence spectroscopy (PL) measurement. Different sapphire substrate regions have different growth conditions of MoS2. The growth of MoS2 is optimized by controlling the amount and location of precursors, adjusting the appropriate growing temperature and time, and establishing proper ventilation. Experimental results show the successful growth of a large-area single-layer MoS2 on a sapphire substrate through direct sulfurization under a suitable environment. The thickness of the MoS2 film determined by AFM measurement is about 0.73 nm. The peak difference between the Raman measurement shift of 386 and 405 cm−1 is 19.1 cm−1, and the peak of PL measurement is about 677 nm, which is converted into energy of 1.83 eV, which is the size of the direct energy gap of the MoS2 thin film. The results verify the distribution of the number of grown layers. Based on the observation of the optical microscope (OM) images, MoS2 continuously grows from a single layer of discretely distributed triangular single-crystal grains into a single-layer large-area MoS2 film. This work provides a reference for growing MoS2 in a large area. We expect to apply this structure to various heterojunctions, sensors, solar cells, and thin-film transistors.

In-situ fabricated amorphous silicon quantum dots embedded in silicon nitride matrix: Photoluminescence control and electroluminescence device fabrication

Herein, we report that high-quality SiN:H films embedded with Si QDs were in-situ fabricated and prepared by the reactive facing target sputtering, which relies on tuning N2 and Ar mixture gas flow ratio. The size of Si QDs in SiN:H films can be tuned from 3.87 nm to 1.40 nm, which exhibit color-tunable photoluminescence from red to blue in the visible region. The microstructure evolution and optical properties of SiN:H films embedded with Si QDs were analyzed by FTIR, Raman, PL, and TRPL measurements, respectively. Considering their unique emission properties, SiN:H films embedded with Si QDs were especially utilized as the emitting layer for fabricating high-performance EL SiN-based LEDs. The broad EL emission properties of the devices were explored by both experimental observations and a theoretical model. This work offers a novel idea to prepare high-quality SiN:H films embedded with Si QDs and a deep understanding of their optoelectronic properties.

Green synthesis and physical properties of crystalline silica engineering nanomaterial from rice husk (agriculture waste) at different annealing temperatures for its varied applications

Crystalline nano silica (SiO2) was synthesized using a cost-effective eco-friendly method from agricultural waste material like rice husk. Polymer nanocomposite has been prepared using the sol-gel technique from crystalline nano silica using PVA as a polymer binder. Thermal analysis measurement is employed to investigate thermal stability. The XRD analysis shows the crystalline nature of silica is revealed to have characteristic peaks of SiO2. The particle size was evaluated using Schererr's formula and found to be in the range of 21–31 nm. FTIR measurement shows the presence of O–Si–O (silane) bond formation. The PL measurement shows broad excitation prominently in the visible region. In the XRD pattern, a major peak of the Nanocomposite is observed at an angular position of 19.5° degree, which is more prominent than that of the PVA with the addition of 0.2 wt percent Nano silica to the PVA composite. SEM provides information on homogeneous distribution. This could be beneficial in terms of higher mechanical qualities as well as multifunctional properties. By hydrogen bonding, the PVA molecules are strongly linked to each SiO2 nanoparticle as measured by FTIR. The stability of materials is confirmed by Zeta Potential and DLS. In the photoluminescence property of SiO2-PVA crystalline Nano silica composite is excited using a radiation wavelength of 200 nm. The indirect bandgap was determined to be 4.28 eV which could be attributed to the 1100 °C annealing temperature. Such materials may be used as a semiconductor material obtained from a direct natural source, rice husk. Thus, in the present research structural, physical, and optical properties of crystalline nano silica and its polymer composite are explored, which leads us to prepare technological grads material from agricultural waste for varied applications including Agriculture to medical science.

Luminescent Amorphous Silicon Oxynitride Systems: High Quantum Efficiencies in the Visible Range.

In recent years, researchers have placed great importance on the use of silicon (Si)-related materials as efficient light sources for the purpose of realizing Si-based monolithic optoelectronic integration. Previous works were mostly focused on Si nanostructured materials, and, so far, exciting results from Si-based compounds are still lacking. In this paper, we have systematically demonstrated the high photoluminescence external quantum efficiency (PL EQE) and internal quantum efficiency (PL IQE) of amorphous silicon oxynitride (a-SiNxOy) systems. Within an integration sphere, we directly measured the PL EQE values of a-SiNxOy, which ranged from approximately 2% to 10% in the visible range at room temperature. Then, we calculated the related PL IQE through temperature-dependent PL measurements. The obtained PL IQE values (~84% at 480 nm emission peak wavelength) were very high compared with those of reported Si-based luminescent thin films. We also calculated the temperature-dependent PL EQE values of a-SiNxOy systems, and discussed the related PL mechanisms.

Investigating spatial macroscopic metastability of perovskite solar cells with voltage dependent photoluminescence imaging

Metastability is a characteristic feature of perovskite solar cell (PSC) devices that affects power rating measurements and general electrical behaviour. In this work the metastability of different types of PSC devices is investigated through current–voltage (I–V) testing and voltage dependent photoluminescence (PL-V) imaging. We show that advanced I–V parameter acquisition methods need to be applied for accurate PSC performance evaluation, and that misleading results can be obtained when using simple fast I–V curves, which can lead to incorrect estimation of cell efficiency. The method, as applied in this work, can also distinguish between metastability and degradation, which is a crucial step towards reporting stabilised efficiencies of PSC devices. PL-V is then used to investigate temporal and spatial PL response at different voltage steps. In addition to the impact on current response, metastability effects are clearly observed in the spatial PL response of different types of PSCs. The results imply that a high density of local defects and non-uniformities leads to increased lateral metastability visible in PL-V measurements, which is directly linked to electrical metastability. This work indicates that existing quantitative PL imaging methods and point-based PL measurements of PSC devices may need to be revisited, as assumptions such as the absence of lateral currents or uniform voltage bias across a cell area may not be valid.

Promising Photoluminescence Enhancement of Tris(8-hydroxyquinoline)aluminum by Simultaneous Localized and Propagating Surface Plasmons of Ag Nanostructures

The continuous performance optimization of tris(8-hydroxyquinoline)aluminum (Alq3) materials is of great significance during the commercialization process of organic light-emitting diodes (OLEDs). In incorporating Ag nanostructures into Alq3, the photophysical properties are greatly improved by the plasmon–exciton coupling effect. Localized surface plasmons (LSPs) in Ag nanoparticles (NPs) efficiently increased the absorption ability. The coexistence of LSPs and propagating surface plasmons (PSPs) in Ag nanowires (NWs) leads to a PL enhancement of 5.3-fold and a full-width at half maximum (FWHM) narrowed by 10 nm. Temperature-dependent PL measurements exhibit that the plasmonic density of states (DOS) increases with decreasing temperature below 40 °C, and the thermal exchange can be accelerated by the introduction of Ag nanostructures. Effective suppression of the thermal accumulation effect is further proved by excitation intensity (EI)-dependent PL measurements. We also found that Ag nanostructures could mainly change the y coordinates in International Commission on Illumination (CIE), leading to a higher brightness. The 5372 K color temperature of an Ag NWs-embedded composite is suitable for daylight-type fluorescent OLEDs. The results would pave an effective way for further optimizing the optical performance of light-emitting materials in OLEDs.

Efficient optical waveguiding and lasing in needle crystals of thiophene/phenylene co-oligomers grown in solution

Needle organic single crystals of light-emitting π-conjugated compounds are superior platforms for photonic circuits. Thiophene/phenylene co-oligomers have been ideal laser media, however, a facile crystal growth method that controls crystal morphologies and optical waveguiding characteristics has not yet been developed. Here, 2,5-bis(4′-cyanobiphenyl-4-yl)thiophene (BP1T-CN) and 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN) are crystallized with needle morphologies in solution. The attenuation coefficients estimated via spatially resolved PL measurements were 0.012 ± 0.006 μm−1 for a BP1T-CN crystal and 0.027 ± 0.003 μm−1 for a BP2T-CN crystal. Furthermore, both exhibited lasing in a Fabry–Pérot mode via self-cavity effects.

Fabrication of UV photodetector based on GaN/ Psi heterojunction using pulse laser deposition method: Effect of different laser wavelengths

In this study, GaN/pSi heterojunction photodetectors were fabricated via pulsed laser deposition method (PLD). Photoelectrochemical etching method (PECE) with laser aid prepared a pSi substrate. Different laser wavelengths were tested on GaN and pSi films' structural, spectroscopic, electrical, and performance characteristics. XRD showed that GaN/pSi heterojunction photodetectors were polycrystalline and hexagonal. PL measurements showed two emission peaks attributable to GaN films (374, 364, 359 nm) and the pSi substrate (730, 729, 729 nm). Shorter laser wavelengths raised the GaN/pSi heterojunction's optical energy gap from 3.271 to 3.3415 eV. FESEM pictures showed that the average size of the manufactured samples was 51.88, 36.12, and 22.76 nm for spherical nanoparticles and a cauliflower-like shape. Atomic force microscopy (AFM) results show the root mean square of the surface roughness of prepared samples to be 4.83, 8.87, and 14.51 nm, respectively, as the laser wavelength became shorter with full coverage of all pores of prepared pSi. GaN/pSi heterojunction photodetectors had rectification in their dark I–V characteristics, and the heterojunction made at 355 nm had the best junction characteristics. The spectral responsivity of GaN/pSi photodetectors shows that the maximum responsivity was 29.01 A/W at 370 nm for a photodetector prepared at 355 nm. High detectivity and external quantum efficiency were 8.02×10+12 Jones and 359.73% at 370 nm, respectively. The photodetector fabricated using 355 nm showed a fast rise time of 328μsec and a fall time of 617μsec.

Study of silicon surface micro‐roughness generated by SF6 remote plasma etching

We investigate micro‐roughness of silicon surface in remote radiofrequency (RF) SF6 plasma, for different etching durations. A linear behavior of etching rate is observed as a function of etching time. PL measurements at different temperatures indicate a visible (green and violet) and ultraviolet (UV) emissions. The evolution of surface roughness of Si substrates can be controlled depending on the etching duration. In response to the increase of the etching duration, the surface undergoes nanoscale roughening, ripple formation, and finally microscale roughening. Atomic force microscopy analysis was carried out to surface morphology.

Structural, optical, photoluminescence, and magnetic properties of Mo0.6−xTi0.3Zn0.1ErxO3 nanorods films fabricated by sol–gel/spin coating technique

Er3+-incorporated Mo0.6−xTi0.3Zn0.1 nanorods thin films were prepared on glass substrates via controlled sol–gel method. The Mo, Zn, Ti, and Er solutions were prepared using ammonium dimolybdate, titanium isopropoxide, zinc acetate dehydrate, and erbium nitrate as the starting material. Ethylene glycol, monoethanolamine, and HCl acid are solvents and solution stabilizers in the sol–gel process. The effect of the Er3+ concentration (0 ≤ x ≤ 0.3 mol%) on the films structure, optical, photoluminescence, and magnetic properties of the nanorods films was investigated by XRD, SEM, Pl, and magnetic measurement. XRD analysis proved that the samples with Er doping = 0.0 and 0.1 consists of single-phase MoO3. By increasing erbium doping to 0.2 and 0.3, bi-phasic were obtained, one of them MoO3 and the other was related to Ti6O11. These results indicate that MoO3 (two-dimensional) can control the internal growth of the Mo0.6−xTi0.3Zn0.1ErxO3 film's structure as supported by SEM and FTIR results. The reflectance of doped films exhibits high values that are increasing with the Er ratio, which adapted an increase in the Eg values from 2.85 to 3.25 eV. The presence of Er3+ in the films is found to sense the photoluminescence process that reveals two emission lines at 1477 and 1543 nm for Er ions. Magnetization behavior for samples exhibits antiferromagnetic behavior with weak ferromagnetic and unsaturated characteristics, where the magnetization at the maximum field (Mmax) increases with increase in Er content.

Substrate-Induced Anisotropic Growth of CuAlO2 Platelets in a Liquid-Solid Reaction.

This study reports a simplified method to grow CuAlO2 crystals of submillimeter sizes with a highly anisotropic shape of a platelet. The solid-state reaction of forming CuAlO2 at ca. 1373 K in the first stage of the conventional flux method is no longer required. The CuAlO2 platelets nucleated directly onto the (0001)sapphire surface in a melt of Cu2O saturated with Al2O3 at 1473 K. The excess flux was mostly removed by the capped alumina plate on cooling with a limited amount of residue which can be leached afterward. The CuAlO2 platelets all have a 3R crystal structure with no line and planar defects observed by TEM. The CuAlO2 crystals emit a luminescence at 3.49 eV associated with resonant Raman effect resulted from a band-to-band transition in room-temperature PL measurement. The facile fabrication method for growing highly anisotropic CuAlO2 crystals paves the way for their practical application in photoelectrochemical devices.

Architecture and Kinetic Studies of Photocatalytic H2O2 Generation and H2 Evolution through Regulation of Spatial Charge Transfer via Z-Scheme Path over a (001) Facet Engineered TiO2@MXene/B-g-C3N4 Ternary Hybrid.

Spatial charge separation and migration are the critical shortcomings dominating the core energy conversion corridors of photocatalytic systems. Here, a biomimetic multi-interfacial architecture providing strong coupled interaction and rapid charge transmission for photostable and competent photocatalytic H2O2 production and H2 evolution is proposed. The triple-hybrid all-solid-state Z-scheme system was formed with the (001) facet exposed TiO2 nanosheets derived from MXene layers and B-g-C3N4 nanosheets (M/(001)TiO2@BCN) through an electrostatic self-assembly strategy with intimate electronic interaction due to Ti orbital modulation and proper stacking among the hybrids. The metallic and highly conductive MXene layers act as solid state electron mediators in the Z-scheme heterojunction that promote electron-hole separation and migration efficiency. Specifically, the MTBCN-12.5 composite provides optimum yield of H2O2 up to 1480.1 μmol h-1 g-1 and a H2 evolution rate of 408.4 μmol h-1 (with ACE 6.7%), which are 4 and 20 fold greater than the pristine BCN, respectively. The enhanced photocatalytic performance is systematically identified by the increased surface area, higher cathodic and anodic current densities of -1.01 and 2.27 mA cm-2, delayed charge recombination as supported by PL and EIS measurement, and excellent photostability. The Z-scheme charge transfer mechanism is validated by time-resolved photoluminescence (TRPL) analysis, cyclic voltametric analysis, and the radical trapping experiment as detected by PL analysis. This research marks a substantial advancement and establishes the foundation for future design ideas in accelerating charge transfer.

Mechanoluminescence, thermoluminescence, optically stimulated luminescence and photoluminescence in SrAl2O4:Eu micro- and nanophosphors: effect of particle size and annealing in different atmospheres.

SrAl2O4:Eu in microcrystalline form was prepared by a combustion method. The formation of the material in a single phase was confirmed by XRD analysis. The material was crushed and sieved to get particles with different particle size ranges. It was further ball milled for 1-7 days to get particles in the nanosize ranges. The broadening of the XRD peaks of the phosphor material in nanocrystalline form was used to determine average particle sizes. The shapes and sizes of these particles could also be seen in FESEM images. The materials thus obtained were annealed in reducing (10% H2 in Ar) and oxidizing (in air) atmospheres at different temperatures for 1.0 h. The increase in the mechanoluminescence (ML) intensity on annealing in a reducing atmosphere at different temperatures and decrease on annealing in an oxidizing atmosphere could be attributed to redox reactions. This was further confirmed by PL measurements. Mechanoluminescence (ML), thermoluminescence (TL), and optically stimulated luminescence (OSL) of the materials were studied. In all three cases (i.e., ML, TL, and OSL), the intensities are found to decrease with the particle size. A large shift of approximately 20 °C in the main peak of TL glow curves of micro- and nanocrystalline materials shows a widening of the band gap due to the particle size effect. A decrease in piezoelectric constant (d33) and field (F V m-1) with particle size was also observed. The present systematic study of particle size effect (over a wide range of particle sizes) on ML has great importance from a technological and application point of view for developing stress sensors.

Compositionally engineered Cd-Mo-Se alloyed QDs toward photocatalytic H2O2 production and Cr(VI) reduction with a detailed mechanism and influencing parameters.

With the exceptional advantages of safety, greenness, and low cost, photocatalytic H2O2 generation has kindled a wonderful spark, although being severely hampered by the terrible photoinduced exciton recombination, migration, and surface decomposition. Here, employing reflux method, the Cd-Mo-Se quantum dots of varying molar ratios of Cd and Mo were synthesized using thioglycolic acid as the capping ligand to regulate their growth. This type of metal alloying promotes rapid charge migration, improves light harvesting, and reduces the rate of charge recombination. The improved optoelectronic properties and boosted activity of Cd-rich ternary CMSe-1 QDs led to the observed exceptional photocatalytic H2O2 yield of 1403.5 μmol g-1 h-1 (solar to chemical conversion efficiency, 0.27%) under visible light, outperforming the other ternary and Se-based QD photocatalysts. Additionally, CMSe-1 shows 93.6% (2 h) hazardous Cr(VI) photoreduction. The enhanced catalytic performance of CMSe-1 corresponds to effective charge carrier separation and transfer efficiency, well supported by PL, TRPL, and electrochemical measurements. Photocatalytic H2O2 production was also studied under varying experimental conditions and the scavenger test suggests a superoxide radical intermediate 2-step single electron reduction pathway. The catalyst-assisted Cr(VI) reduction is substantiated by the zero-order kinetics as well as the determination of the pHPZC value. The catalyst can be employed for a maximum of four times while retaining its activity, according to the photostability and reusability test outcomes. This research presents interesting approaches for producing ternary QDs and modified systems for efficient photocatalytic H2O2 production and Cr(VI) reduction.