Warm red light emitting Eu(III) complexes synthesis and analysis including computational methods for photonic applications.

Six luminescent europium organic complexes have been synthesized and studied for their luminescent properties. The synthesized complexes were analyzed through elemental analysis, XRD, SEM, EDAX, FT-IR, NMR and thermogravimetry. The complexes exhibit crystalline behavior and possess decent thermal stability. Photoluminescence study on complexes were conducted in both solid and solution states, the results indicate the characteristic red emission. With the addition of ancillary ligands, water molecules are replaced from inner coordination sphere, leading to enhanced luminescence properties. The colorimetric parameters (CIE, CP%, CCT, u', v') suggest aptness of these complexes in red light illuminating OLEDs. The J-O parameters were calculated experimentally and theoretically with the help of LUMPAC software. Theoretical and experimental results agree well reflecting the efficacy of the outcomes. As a result of red emission, these complexes could have interesting photonics applications. The biological studies indicate the probable use of these complexes in the medical industry.

Extreme Electron-Photon Interaction in Disordered Perovskites.

The interaction of light with solids can be dramatically enhanced owing to electron-photon momentum matching. This mechanism manifests when light scattering from nanometer-sized clusters including a specific case of self-assembled nanostructures that form a long-range translational order but local disorder (crystal-liquid duality). In this paper, a new strategy based on both cases for the light-matter-interaction enhancement in a direct bandgap semiconductor - lead halide perovskite CsPbBr3 - by using electric pulse-driven structural disorder, is addressed. The disordered state allows the generation of confined photons, and the formation of an electronic continuum of static/dynamic defect states across the forbidden gap (Urbach bridge). Both mechanisms underlie photon-momentum-enabled electronic Raman scattering (ERS) and single-photon anti-Stokes photoluminescence (PL) under sub-band pump. PL/ERS blinking is discussed to be associated with thermal fluctuations of cross-linked [PbBr6]4- octahedra. Time-delayed synchronization of PL/ERS blinking causes enhanced spontaneous emission at room temperature. These findings indicate the role of photon momentum in enhanced light-matter interactions in disordered and nanostructured solids.

Synthesis and Optical Properties of Organic-Inorganic Hybrid [(18-Crown-6)K][MoOCl4(H2O)].

Crown ether anchored organic-inorganic hybrid halides have been recently reported as interesting luminescent materials in the visible region of electromagnetic spectrum. Is it possible to develop such crown ether anchored hybrid materials for near infrared emission? Motivated by this question, we designed a new hybrid material, namely, [(18-Crown-6)K][MoOCl4(H2O)]. 18-Crown-6 ether bound with K+ form the cationic part [(18-Crown-6)K]+. The K+ of [(18-Crown-6)K]+ electrostatically interacts with Cl- of the anionic part [MoOCl4(H2O)]-, forming the hybrid crystal [(18-Crown-6)K][MoOCl4(H2O)]. It crystallizes in orthorhombic crystal system with Pnma space group. The Mo(V) possesses one d-electron (d1) in C4v point group symmetry in the [MoOCl4(H2O)]- polyhedra. This electronic configuration leads to multiple spin-allowed d-d transitions along with a ligand to metal charge transfer (LMCT) resulting into multiple optical absorption bands in the near UV-visible-near infrared (NIR) region. The lowest energy d-d transition via 2E  to 2B2 leads to NIR PL with peak at 952 nm, but with a poor intensity at room temperature.

Photoluminescent and Electrochemiluminescent Detection of Fe3+ Using Cyclometalated Iridium Complexes via Fe3+-Catalyzed Hydrolysis.

Ferric ion (Fe3+) is a biologically abundant and important metal ion. We developed several cyclometalated iridium complex-based molecular sensors (1, ppy-1, 1-phen, 1a, and 1-OMe) for the detection of Fe3+ using an acetal moiety as the reaction site. The acetal moiety in iridium complexes undergoes Fe3+-catalyzed hydrolysis and subsequent formation of a formyl group, resulting in turn-off photoluminescent and electrochemiluminescent responses. Sensor 1 showed excellent selectivity toward Fe3+ over other biologically important metal ions. Furthermore, we compared the performance of the sensors based on the structural differences of the iridium complexes, and revealed a relationship between the structure and chemical properties through electrochemical experiments and computational calculations.

Giant Valley Zeeman Splitting in Vanadium-Doped WSe2 Monolayers.

2D dilute magnetic semiconductors (DMS) based on transition metal dichalcogenides (TMD) offer an innovative pathway for advancing spintronic technologies, including the potential to exploit phenomena such as the valley Zeeman effect. However, the impact of magnetic ordering on the valley degeneracy breaking and on the enhancement of the optical transitions g-factors of these materials remains an open question. Here, a giant effective g-factors ranging between ≈-27 and -69 for the bound exciton at 4 K in vanadium-doped WSe2 monolayers, obtained through magneto-photoluminescence (PL) experiments is reported. This giant g-factor disappears at room temperature, suggesting that this response is associated with a magnetic ordering of the vanadium impurity states at low temperatures. Ab initio calculations for the vanadium-doped WSe2 monolayer confirm the existence of magnetic ordering of the vanadium states, which leads to degeneracy breaking of the valence bands at K and K'. A phenomenological analysis is employed to correlate this splitting with the measured enhanced effective g-factor. The findings shed light on the potential of defect engineering of 2D materials for spintronic applications.

Suppressing energy migration via antiparallel spin alignment in one-dimensional Mn2+ halide magnets with high luminescence efficiency.

Photoexcited energy migration is prone to causing luminescence quenching in Mn2+ luminescent materials, presenting a formidable challenge for optoelectronic applications. Although various strategies and mechanisms have been proposed to mitigate this issue, the role of spin alignment between adjacent Mn2+ ions has remained largely unexamined. In this study, we have elucidated the influence of spin alignment on energy migration within the one-dimensional Mn2+-metal halide compound (CH3)4NMnCl3 (TMMC) through variable-temperature photoluminescence (PL) and magnetic-optical spectroscopy. This investigation was conducted with reference to (CH6N3)2MnCl4 (GUA) with isolated [Mn3Cl12]6- trimers and Cd2+-doped TMMC. The spin order in TMMC below approximately 55 K is demonstrated by the disorder-order transition observed in the temperature-dependent magnetic susceptibility. This finding is further corroborated by the negligible shift in the temperature- and field-dependent emission peaks, a consequence of magnetic saturation. Our results indicate that the antiparallel spin alignment along the Mn2+ chain in TMMC effectively suppresses energy migration and multiphonon relaxation, thereby reducing nonradiative transitions and enhancing the photoluminescence quantum yield (PLQY).This research casts new light on the potential for developing high-performance Mn2+-doped phosphors for optoelectronic and spin-photonic applications, offering insights into the manipulation of spin and energy dynamics in these materials.

Au25 Cluster-Based Atomically Precise Coordination Frameworks and Emission Engineering through Lattice Symmetry.

The atomically precise metal nanoclusters (NCs) have attracted significant attention due to their superatomic behavior originating from the quantum confinement effect. This behavior makes these materials suitable for various photoluminescence-based applications, including chemical sensing, bioimaging, and phototherapy, owing to their intriguing optical properties. Especially, the manipulation of inter- or intracluster interaction through cluster-assembled materials (CAMs) presents significant pathways for modifying the photophysical properties of NCs. Herein, two distinct CAMs, Au25-Zn-Hex and Au25-Zn-Rod, were synthesized via forming a coordination bond between [Au25(p-HMBA)18]- (p-H2MBA = 4-mercaptobenzoic acid) and Zn2+. Au25-Zn-Rod exhibited a 6-fold higher luminescence intensity in the near-infrared region compared to Au25-Zn-Hex, attributed to synergistic inter- and intracluster interactions that induce exciton delocalization and structure rigidification at the atomic scale. This study highlights the potential of diverse lattice symmetries in cluster-based frameworks for tuning the photophysical properties, contributing to a deeper understanding of the structure-property relationship in Au NCs.

Indirect-To-Direct Bandgap Crossover and Room-Temperature Valley Polarization of Multilayer MoS2 Achieved by Electrochemical Intercalation.

Monolayer (1L) group VI transition metal dichalcogenides (TMDs) exhibit broken inversion symmetry and strong spin-orbit coupling, offering promising applications in optoelectronics and valleytronics. Despite their direct bandgap, high absorption coefficient, and spin-valley locking in K or K' valleys, the ultra-short valley lifetime limits their room-temperature applications. In contrast, multilayer TMDs, with more absorptive layers, sacrifice the direct bandgap and valley polarization upon gaining inversion symmetry from the bilayer structure. It is demonstrated that multilayer molybdenum disulfide (MoS2) can maintain 1) a structure with broken inversion symmetry and strong spin-orbit coupling, 2) a direct bandgap with high photoluminescence (PL) intensity, and 3) stable valley polarization up to room temperature. Through the intercalation of organic 1-ethyl-3-methylimidazolium (EMIM+) ions, multilayer MoS2 not only exhibits layer decoupling but also benefits from an electron doping effect. This results in a hundredfold increase in PL intensity and stable valley polarization, achieving 55% and 16% degrees of valley polarization at 3 K and room temperature, respectively. The persistent valley polarization at room temperature, due to interlayer decoupling and trion dominance facilitated by a gate-free method, opens up potential applications in valley-selective optoelectronics and valley transistors.

High temperature photoluminescence dependence and energy migration of Tb3+-Incorporated K3Y(BO2)6 phosphors.

This study investigates the structural and photoluminescence (PL) characteristics of Tb3+-incorporated K3Y(BO2)6 (KYBO) phosphors synthesized via a microwave-assisted sol-gel technique. X-ray diffraction (XRD) and Rietveld refinement confirmed the formation of a pure hexagonal phase, with lattice expansion due to Tb³âº doping. PL studies revealed strong green emissions centered at 541 nm, attributed to the 5D4 → 7F5 transitions of Tb³âº ions, with the highest intensity observed at 5 wt% Tb³âº. A decrease in emission was observed at higher concentrations due to concentration quenching. Temperature-dependent PL measurements revealed reverse thermal quenching enhancing PL intensity. Chromaticity analysis based on CIE 1931 coordinates showed stable green emission across all concentrations, with a maximum color purity of 89.74% observed for the KYBO:3 wt% Tb³âº sample. The results, along with reverse thermal quenching behavior observed between 470K and 550K, suggest that these phosphors exhibit excellent potential for lighting and display technologies.

PARAFAC under non-negativity constraint is adapted to recover the underlying Beer-Lambert law of the excitation-emission fluorescence matrix measurements acquired from analyte-triggered semiconductor QDs photoluminescence modulation. When and why?

BACKGROUND: Analyte-triggered semiconductor quantum dots (QDs) modulation in the presence of non-consistently responsive fluorescent species represents a challenging analytical issue in concrete multi-way data handling. QDs with heterogeneous sizes and/or uneven distribution of functional moieties on their surfaces exhibit significant fluctuations in the fluorescent response components, known as chemical rank, across different excitation/emission modes. This phenomenon may lead to a substantial deviation from the proportionality prescribed by Beer-Lambert law. Nonetheless, even in the presence of such deviation, a multi-way model may be successfully selected after determining a proper chemical rank in a QDs system. RESULTS: We show that in a valid PARAllel FACtor (PARAFAC) model under properly determined chemical rank, meaningfully resolved pure spectral profiles can be reached for each fluorescent responsive constituent in the original excitation-emission fluorescence matrix (EEFM) measurements. This was thoroughly illustrated by applying PARAFAC trilinear decomposition of a three-way data array of two distinct datasets acquired from semiconductor QDs sensing systems with low-rank trilinear assumption. The first dataset, presented here for the first time, comprises EEFM measurements of the ligand-driven quenching of thiomalic acid (TMA)-capped AgInS2 (AIS) QDs by vomitoxin. The second dataset, employed for illustrative purposes, comprises EEFM measurements of the quenching, via cation bridging, of glutathione (GSH)-capped CdTe QDs by Pb(II). The results of this study enabled the determination of vomitoxin at a ppb level in real samples of fish feeds, showcasing the efficacy of the PARAFAC model in resolving spectral signatures (loadings) and pure concentration profiles (scores). SIGNIFICANCE: PARAFAC under a properly examined chemical rank can be easily adapted for retrieval the underlying Beer-Lambert law of the original EEFM measurements with a low-rank trilinear structure through the chemically meaningful information either when (i) no deviation of Beer-Lambert law was observed as deeply discussed in connection with the dataset acquired from vomitoxin-driven molecular sensing through TMA-capped AIS QDs, or when (ii) substantial deviations of the Beer-Lambert law are evident, as discussed in connection with the dataset collected from sensing ionic species through Pb(II) bridging of GSH-capped CdTe QDs.

Impact of the Interruption Duration on Photoluminescence Properties of MOCVD-Grown GaAsP/InAlGaAs Quantum Well Structures.

The growth interruption technology is introduced to the growth of GaAsP/InAlGaAs quantum well (QW) structure using metal-organic chemical vapor deposition (MOCVD). The effect of growth interruption time (GIT) on the crystalline quality and optical properties are investigated. The two distinctive emission peaks are the transition recombination between the electron level of conduction band and the light and heavy hole level of valence band in the photoluminescence (PL) at room temperature. The PL peaks present a redshift and merge together with the increasing GIT, which is attributed to the QW energy level shift caused by the increase in arsenic concentrations in GaAsP QW, the diversified thickness of QW and the variations of indium components in the InAlGaAs barrier layer. The Gaussian deconvolution parameters in temperature-dependent PL (TDPL) show that the GaAsP/InAlGaAs QW with a GIT of 6 s has a 565.74 meV activation energy, enhancing the carrier confinement in QW and the PL intensity, while the 6 s-GIT GaAsP QW has the increasing interface roughness and the non-radiative centers at the InGaAsP intermediate layer, leading to a spectral broadening. The QW with 10 s-GIT exhibits a small full width at half maximum (FWHM) with the various temperature, indicating reduced interface roughness and excellent crystal quality. An increase in GIT may be suitable for optimizing the optical properties of GaAsP/InAlGaAs QW.

Different Optical Behaviors Revealed by Electroluminescence and Photoluminescence of InGaN/GaN Coupled Quantum Wells.

The optical properties of wurtzite violet InGaN/GaN coupled quantum well (QW) structures are experimentally studied using photoluminescence (PL) and electroluminescence (EL) spectroscopy. Two emission peaks, referred to as Peak H and Peak L, are observed in both PL and EL spectra, due to the ground state splitting induced by the well coupling. Experimental PL and EL results reveal that coupled QWs show different optical responses due to the different variation in the electric field inside the QW structure. Since the direction of the polarization electric field of the as-grown well/barrier layers is different, the external electric field applied by electrodes can change the energy band alignment between the well and the barrier layers, thus adjusting the coupling between the wells. Our results provide relevant information to improve our understanding of the optical properties of InGaN/GaN QWs and to develop novel optoelectronic devices.

Coulomb Contribution to Shockley-Read-Hall Recombination.

A nonradiative recombination channel is proposed, which does not vanish at low temperatures. Defect-mediated nonradiative recombination, known as Shockley-Read-Hall (SRH) recombination, is reformulated to accommodate Coulomb attraction between the charged deep defect and the approaching free carrier. It is demonstrated that this effect may cause a considerable increase in the carrier velocity approaching the recombination center. The effect considerably increases the carrier capture rates. It is demonstrated that, in a typical semiconductor device or semiconductor medium, the SRH recombination rate at low temperatures is much higher and cannot be neglected. This effect renders invalid the standard procedure of estimating the radiative recombination rate by measuring the light output in cryogenic temperatures, as a significant nonradiative recombination channel is still present. We also show that SRH is more effective in the case of low-doped semiconductors, as effective screening by mobile carrier density could reduce the effect.

Robust and orange-yellow-emitting Sr-rich polytypoid α-SiAlON (Sr3Si24Al6N40:Eu2+) phosphor for white LEDs.

Nitrides and oxynitrides isostructural to α-Si3N4 (M-α-SiAlON, M = Sr, Ca, Li) possess superb thermally stable photoluminescence (PL) properties, making them reliable phosphors for high-power solid-state lighting. However, the synthesis of phase-pure Sr-α-SiAlON still remains a great challenge and has only been reported for Sr below 1.35 at.% as the large size of Sr2+ ions tends to destabilize the α-SiAlON structure. Here, we succeeded to synthesize the single-phase powders of a unique 'Sr-rich' polytypoid α-SiAlON (Sr3Si24Al6N40:Eu2+) phosphor with three distinctive Sr/Eu luminescence sites using a solid-state remixing-reannealing process. The Sr content of this polytypoid structure exceeds those of a few previously reported structures by over 200%. The phase purity, composition, structure, and PL properties of this phosphor were investigated. A single phase can be obtained by firing the stoichiometric mixtures of all-nitride precursors at 2050°C under a 0.92 MPa N2 atmosphere. The Sr3Si24Al6N40:Eu2+ shows an intense orange-yellow emission, with the emission maximum of 590 nm and internal/external quantum efficiency of 66%/52% under 400 nm excitation. It also has a quite small thermal quenching, maintaining 93% emission intensity at 150°C. In comparison to Ca-α-SiAlON:Eu2+, this Sr counterpart shows superior quantum efficiency and thermal stability, enabling it to be an interesting orange-yellow down-conversion luminescent material for white LEDs. The experimental confirmation of the existence of such 'Sr-rich' SiAlON systems, in a single-phase powder form, paves the way for the design and synthesis of novel 'Sr-rich' SiAlON-based phosphor powders with unparalleled properties.

A distinctive orange-yellow-emitting 'Sr-rich' α-SiAlON-based phosphor with quite small thermal quenching (93% PL intensity at 150°C) that can surprisingly be synthesized in a single-phase powder form for white LEDs.

Development and Test of Low-Cost Multi-Channel Multi-Frequency Lock-In Amplifier for Health and Environment Sensing.

Optical-based sensing techniques and instruments, such as fluorometric systems, absorbance-based sensors, and photoacoustic spectrometers, are important tools for detecting food fraud, adulteration, and contamination for health and environmental purposes. All the aforementioned optical equipments generally require one or more low-frequency Lock-In Amplifiers (LIAs) to extract the signal of interest from background noise. In the cited applications, the required LIA frequency is quite low (up to 1 kHz), and this leads to a simplification of the hardware with consequent good results in portability, reduced size, weight, and low-cost characteristics. The present system, called ENEA DSP Box Due, is based on a very inexpensive microcontroller proto-board and can replace four commercial LIAs, resulting in significant savings in both cost and space. Furthermore, it incorporates a dual-channel oscilloscope and a sinusoidal function generator. This article outlines the architecture of the ENEA DSP Box Due, its electrical characterization, and its applications within a project concerning laser techniques for food and water safety.

Synthesis and Properties of Dibenzo-Fused Naphtho[2,3-b:6,7-b']disilole and Naphtho[2,3-b:6,7-b']diphosphole.

Silole- and phosphole-containing polycyclic aromatic compounds have attracted significant attention in the field of organic functional materials. The structure of the aromatic units has great impact on the photophysical properties of the resulting silole- and phosphole-containing polycyclic aromatic compounds. Here, dibenzo-fused naphtho[2,3-b:6,7-b']disilole (NDS) and naphtho[2,3-b:6,7-b']diphosphole (NDP), where a naphthalene unit is arranged between two silole and phosphole units, respectively, were designed and synthesized. The solid-state structures of them were confirmed by X-ray crystallographic analysis. The photophysical properties were evaluated by UV-vis absorption and photoluminescence spectroscopies and compared with those of their related compounds, such as dibenzo-fused silolo[3,2-b]silole and benzo[1,2-b:4,5-b']disilole, ever reported. The longest wavelength absorption band of a series of silole-fused compounds was found to be red-shifted in the order benzo[1,2-b:4,5-b']disilole < NDS < silolo[3,2-b]silole derivatives. For a series of phosphole-fused compounds, π-extension from phospholo[3,2-b]phosphole to NDP derivatives induces the lower absorption coefficient of the longest wavelength absorption band and the red-shift of the second longest wavelength absorption band. Both NDS and NDP exhibit much lower fluorescence quantum yields than their related compounds.

Super-Spectral-Resolution Raman spectroscopy using angle-tuning of a Fabry-Pérot etalon with application to diamond characterization.

Raman spectroscopy is an extremely powerful laser-based method for characterizing materials based on their unique inelastic scattering spectrum. Ultimately, the power of the technique is limited by the resolution of the spectrometer. Here we introduce a new method for achieving Super-Spectral-Resolution Raman Spectroscopy (SSR-RS), by angle-tuning a Fabry-Pérot (F-P) etalon filter that we incorporated in a micro-Raman setup. A monolithically coated F-P etalon structure, only 1.686 mm in thickness, was mounted onto an angle-tunable motorized stage, and Raman spectra were automatically acquired for many different angles of the etalon. Using a low-resolution grating of 150 g/mm by itself, without the F-P etalon, we obtained a best-case regular Raman spectral linewidth of 44 cm-1 for the characteristic Raman peak from a diamond sample. When we applied the SSR-RS technique to diamond, we obtained a super-spectral resolution peak that was 27x narrower, namely 1.63 cm-1, and a Raman shift of 1331.3 cm-1. To baseline SSR-RS, we applied the super-spectral-resolution method to extract the linewidth and peak wavelength of the laser excitation itself and obtained a laser linewidth of better than 0.014 cm-1, with a laser wavelength centered at 531.962 nm, close to the stated wavelength of 532 nm. This extracted laser linewidth is 3300x times narrower compared to its measured linewidth of 46 cm-1. Thus, our work suggests that SSR-RS can be very generally applied to greatly improve the resolution and precision of Raman instrumentation, and potentially lower the cost of obtaining high-resolution Raman spectroscopic capabilities.

Intrinsic physiochemical insights to green synthesized Ag-decorated GO nanosheet for photoluminescence and in vivo cellular biocompatibility with embryonic zebrafish.

The advancement of nanotechnology and their application has intrigued a significant interest in green synthesis and application of organic and inorganic nanomaterials like graphene oxide (GO) and silver nanoparticles (AgNP). This study explores the intrinsic physiochemical properties of silver (Ag)-decorated graphene oxide (GO) nanosheets synthesized via a green approach, focusing on their photoluminescence behaviour and in vivo cellular biocompatibility with embryonic zebrafish. The nanocomposites were characterized using various spectroscopic and microscopic techniques to elucidate their structural and optical properties. Results reveal that the Ag-decorated GO nanosheets exhibit enhanced photoluminescence compared to pristine GO with an SPR at 405 nm and emission at 676 nm, attributed to the synergistic effects of Ag nanoparticles and GO. In addition, in vivo biocompatibility assessments using embryonic zebrafish demonstrate minimal cytotoxicity and high cellular viability upon exposure to the nanocomposites with an LC50 of 38 µg/ml, indicating their potential for biomedical applications. Further investigations into the interactions between the nanomaterials and biological systems provide valuable insights into their safety profile and suggest their suitability for various biomedical and therapeutic applications. Overall, this study offers a comprehensive understanding of the physiochemical characteristics and biological compatibility of Ag-decorated GO nanosheets, contributing to the advancement of nanotechnology in biomedicine and related fields.

Direct Synthesis of Perovskite Quantum Dot Photoresist for Direct Photolithography.

Perovskite quantum dots (PQDs) photoresists are promising building blocks for photolithographically patterned devices. However, their complex synthesis and combination processes limit their optical properties and potential patterning applications. Here, we present an exceptionally simple strategy for the synthesis of PQDs photoresist. Unlike traditional approaches that involve centrifugation, separation, and combination processes, our direct synthesis technique using polymerizable acrylic monomer as solvent to fabricate PQDs photoresists without complex post-synthesis process. We demonstrate that the change in solubility of the precursors is the main reason for the formation of PQDs in the polymerizable monomer. By direct photolithography, colorful PQD patterns with high photoluminescence quantum yields and excellent fluorescence uniformity are successfully demonstrated. This work opens a new avenue for the direct synthesis of PQDs photoresist, expanding their applications in various integrated applications, such as photonic, energy harvesting, and optoelectronic devices.

Quantum control of polariton emission in a microcavity-quantum well system under magnetic field.

In this work, a quantum dissipative model is employed to investigate the influence of a perpendicular magnetic field on the photoluminescence (PL) spectrum of a quantum well embedded within a microcavity. This model incorporates both the exact electron-hole interaction within the semiconductor and the light-matter coupling between the fundamental photonic mode and the fermionic particles. The loss and pumping mechanisms are described using the quantum master equation, and the PL spectrum is determined via the quantum regression theorem. Our findings demonstrate that the magnetic field acts as a control mechanism in the polariton emission energy, the emission linewidth and the intensity distribution along the emission line. Finally, it is observed that the magnetic field can redistribute the density matrix occupations leading to modifications in the average number of polaritons in the system.