Enhancement Of Photoluminescence Quantum Yield Research Articles

Cs2NaGdCl6:Tb3+─A Highly Luminescent Rare-Earth Double Perovskite Scintillator for Low-Dose X-ray Detection and Imaging.

Rare-earth-based double perovskite (DP) X-ray scintillators have gained significant importance with low detection limits in medical imaging and radiation detection owing to their high light yield (LY) and remarkable spatial resolution. Herein, we report the synthesis of 3D double perovskite (DP) crystals, namely, Cs2NaGdCl6 and Tb3+-Cs2NaGdCl6 using hydrothermal reaction. Cs2NaGdCl6 DP single crystals exhibited a blue self-trapped exciton (STE) emission at 470 nm under ultraviolet (265 nm) excitation with a photoluminescence quantum yield (PLQY) of 8.4%. Introducing Tb3+ ions into Cs2NaGdCl6 has resulted in quenching of STE emission and enhancing green emission at 549 nm attributed to the 5D4 → 7F5 transition of Tb3+, suggesting efficient energy transfer (ET) from STE to Tb3+. This ET process is evidenced by the appearance of Tb3+ bands in the excitation spectra of the host, the shortening of the STE lifetimes in the presence of Tb3+ ions, and the enhancement of PLQY (72.6%). Furthermore, Cs2NaGdCl6:5%Tb3+ films of various thicknesses (0.1-0.6 mm) were synthesized and their X-ray scintillating performance has been examined. The Cs2NaGdCl6:5%Tb3+ film with 0.4 mm thickness has exhibited an excellent linear response to the X-ray dose rate with a low detection limit of 41.32 nGyair s-1, an LY of 39,100 photons MeV-1, and excellent radiation stability. Benefiting from the strong X-ray excited luminescence (XEL) of Cs2NaGdCl6:5%Tb3+, we developed a Cs2NaGdCl6:5%Tb3+ X-ray scintillator screen with a least thickness (0.1 mm), exhibiting remarkable imaging ability with a spatial resolution of 10.75 lp mm-1. These results suggest that Cs2NaGdCl6:Tb3+ can be a potential candidate for low-dose and X-ray imaging applications.

Ultrastability and color-tunability of CsPbI3 nanocrystals glass via doping CoBr2 and application in WLED

Extensive research has been conducted on all-inorganic CsPbI3 nanocrystals (NCs) due to their exceptional optical properties. In this study, we successfully prepared CoBr2-doped CsPbI3 NCs in Lithium-borosilicate using the conventional melting quenching approach. We investigated the optical characteristics of CsPbI3 NCs glass doped with varying amounts of CoBr2. Remarkably, the samples exhibited outstanding water and thermal stability and tunable emission ranging from 702 to 652 nm. Interestingly, the CsPbI3 NCs glasses doped with CoBr2 demonstrated significantly enhanced photoluminescence quantum yields (PLQYs), which increased from 8 % to 32 %. Furthermore, by mixing a red CsPbI3 NCs glass doped with 0.5 mol CoBr2 and a green CsPbBr3 under a blue LED chip, we effectively generated a WLED which achieved (0.3341, 0.3360) of chromaticity coordinate (CIE), 5775.35 K of a correlated color temperature (CCT) that close to positive white light (0.330, 0.330) and the color rendering index (CRI) 79.4. This study provides a new technique in the field of metal ion-doped perovskite NCs, providing a valuable reference for future research and demonstrating possible applications in LEDs.

Enhancing energy transfer via inhibition defect density of coupled quasi-2D perovskite layers for efficient sky-blue light-emitting diodes

Metal halide perovskite materials have emerged as unique and promising candidates for full-color display and solid-state lighting applications. While substantial progress has been made in developing green, red and near-infrared perovskite light-emitting diodes (PeLEDs) with external quantum efficiency (EQE) approaching their theoretical upper limit, the performance of blue PeLEDs is still lagging far behind. Here, synergistic long and short hydrobromide chains are strategically introduced into the perovskite to regulate composition and dimensional engineering for promoting coupled quasi-two-dimensional perovskite thin films with enhanced photoluminescence quantum yield (PLQY) and reduced trap state density. The inclusion of the hydrobromide can also simultaneously passivate the perovskite defects by reducing nonradiative recombination loss and increasing the formation of n >1 phases for efficient exciton energy transfer. Encouraged by these findings, we finally demonstrate the most stable sky-blue PeLEDs to date with a half-lifetime of 515 min at high external quantum efficiency (EQE＞10 %), emitting at 486 nm with a peak EQE of up to 15.6 %.

Modulation of Heterotypic and Homotypic Interactions to Visualize the Evolution of Organic Aggregates in a Fluorescence Turn-on Manner.

The abnormal evolution of membrane-less organelles into amyloid fibrils is a causative factor in many neurodegenerative diseases. Fundamental research on evolving organic aggregates is thus instructive for understanding the root causes of these diseases. In-situ monitoring of evolving molecular aggregates with built-in fluorescence properties is a reliable approach to reflect their subtle structural variation. To increase the sensitivity of real-time monitoring, we presented organic aggregates assembled by TPAN-2MeO, which is a triphenyl acrylonitrile derivative. TPAN-2MeO showed a morphological evolution with distinct turn-on emission. Upon rapid nanoaggregation, it formed non-emissive spherical aggregates in the kinetically metastable state. Experimental and simulation results revealed that the weak homotypic interactions between the TPAN-2MeO molecules liberated their molecular motion for efficient non-radiative decay, and the strong heterotypic interactions between TPAN-2MeO and water stabilized the molecular geometry favorable for the non-fluorescent state. After ultrasonication, the decreased heterotypic interactions and increased homotypic interactions acted synergistically to allow access to the emissive thermodynamic equilibrium state with a decent photoluminescence quantum yield (PLQY). The spherical aggregates were eventually transformed into micrometer-sized blocklike particles. Under mechanical stirring, the co-assembly of TPAN-2MeO and Pluronic F-127 formed uniform fluorescent platelets, inducing a significant enhancement in PLQY. These results decipher the stimuli-triggered structural variation of organic aggregates with concurrent sensitive fluorescence response and pave the way for a deep understanding of the evolutionary events of biogenic aggregates.

Efficient Near‐Infrared Organic Light‐Emitting Diodes with Emission Peak Above 900 nm Enabled by Enhanced Photoluminescence Quantum Yields and Out‐Coupling Efficiencies

AbstractNear‐infrared organic light‐emitting diodes (NIR OLEDs) with emission peak above 900 nm are attractive for many emerging applications, spanning from bioimaging to light detection and ranging. However, the device performance of NIR OLEDs is generally limited by the low quantum efficiency of emitters because of the fast nonradiative transition process imposed by energy‐gap law and aggregation quenching. So far, only a few Pt(II) complexes delivering external quantum efficiency (EQE) over 1% are reported, while there is no comparable electroluminescence in heavy‐metal‐free fluorescent organic emitters. Here, NIR OLEDs centered at 934 nm by blending an acceptor–donor–acceptor type molecule Y11 into a polymer host poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐(4,4′‐(N‐(4‐sec‐butylphenyl)diphenylamine) (TFB) are reported. The OLEDs show a remarkably high EQE of 1.72%. Moreover, owing to a low turn‐on voltage (≈0.9 V), the resultant NIR OLEDs have an electricity‐to‐light power efficiency surpassing 20 mW W−1. The improved device performance can be attributed to enhanced photoluminescence quantum yields (PLQYs) of the blends owing to suppressed aggregation quenching, and favorable light extraction from the emissive layer. Such values are the highest among fluorescent OLEDs with electroluminescence above 900 nm.

Enhanced Photoluminescence Quantum Yield of Colloidal MoS2 Quantum Dots by Optimization of Oleic Acid and Oleylamine for Light-Emitting Diode Applications

Enhanced Photoluminescence Quantum Yield of Colloidal MoS₂ Quantum Dots by Optimization of Oleic Acid and Oleylamine for Light-Emitting Diode Applications

Optical grade transformation of monolayer transition metal dichalcogenides via encapsulation annealing.

Monolayer transition metal dichalcogenides (TMDs) have emerged as highly promising candidates for optoelectronic applications due to their direct band gap and strong light-matter interactions. However, exfoliated TMDs have demonstrated optical characteristics that fall short of expectations, primarily because of significant defects and associated doping in the synthesized TMD crystals. Here, we report the improvement of optical properties in monolayer TMDs of MoS2, MoSe2, WS2, and WSe2, by hBN-encapsulation annealing. Monolayer WSe2 showed 2000% enhanced photoluminescence quantum yield (PLQY) and 1000% increased lifetime after encapsulation annealing at 1000 °C, which are attributed to dominant radiative recombination of excitons through dedoping of monolayer TMDs. Furthermore, after encapsulation annealing, the transport characteristics of monolayer WS2 changed from n-type to ambipolar, along with an enhanced hole transport, which also support dedoping of annealed TMDs. This work provides an innovative approach to elevate the optical grade of monolayer TMDs, enabling the fabrication of high-performance optoelectronic devices.

Composition-dependent photoluminescence in nanocrystalline La2Hf2-xZrxO7:Eu phosphor: role of chemical twin Zr/Hf environments around a luminescent center.

Based on chemical intuition, linear trends are anticipated in Eu3+ photoluminescence performance inside a pyrochlore matrix of the chemical twins, Hf and Zr, owing to probable geometrical and chemical similarity around the luminescent center. The present work reports the drastically fluctuating result of doping Eu3+ in nanocrystalline pyrochlore, La2Hf2-xZrxO7 (LHZO), matrix on composition variation; the variation is counter to the anticipation-based chemical brotherhood of Hf and Zr. Zirconium-enriched samples of LHZO improve asymmetry around Eu3+ ion leading to enhanced photoluminescence quantum yield (PLQY). The samples with compositions 0.7Hf and 1.3Zr depict the lowest non-radiative channels with the highest theoretically calculated PLQY of ∼71% and excellent thermal stability (∼91%). Synergistic experimental and theoretical analysis reveals that Eu does not unbiasedly occupy La-sites in the pyrochlore LHZO matrix towards chemical twins of Hf and Zr; rather, it energetically prefers to occupy Zr-rich vicinal sites. When the composition with Zr is in the low-medium range, Eu has a higher probability of occupying Zr-rich vicinal sites depicting higher lifetime and PLQY. When Zr-content goes beyond 70-80%, the other site occupancies start contributing leading to a reduction in both lifetime and quantum yield. This work paves a great strategy and provides a futuristic potential to utilize europium luminescence in separating chemically close Hf-Zr for various technological applications.

Tunable efficient visible and near-infrared multi-emission in Ho3+ doped Cs2NaBiCl6 double perovskite via Ag+ alloying

Herein, we successfully obtained Ho3+ and Ag+ -codoped Cs2NaBiCl6 halide double perovskites (DPs) via a hydrothermal method, which exhibit orange-red broadband self-trapped excitons (STE) emission and visible (Vis) and near-infrared (NIR) narrow band emission attributed to Ho3+f-f transition, under 360 nm excitation. Compared to the single Ho3+-doped sample, the Vis PL intensity of the codoped sample was increased by nearly 13.8 times, and an enhanced photoluminescence quantum yield (PLQY) of 87.45 % was achieved. The PL enhancement is attributed to the partial substituting of Na+ with Ag+, leading to an efficient STE emission, and the more energy transition from STE to Ho3+. Moreover, the synthesized phosphor exhibits good stability in thermal and atmospheric environments. White light-emitting diode (WLED) is fabricated by employing Cs2Na0·997Ag0·003Bi0.935Ho0.065Cl6 on near-ultraviolet (n-UV) LED chips, achieving a color rendering index (CRI) of 95.0 and correlated color temperature (CCT) of 3814 K. Anti-counterfeit patterns and the application for night vision monitoring were also discussed. This study inspires the designing of high-quality phosphors of rare earth-doped DPs and expands the multi-domain luminescence applications of halide DPs.

Enhanced photoluminescence quantum yield and stability of CsPbBr3 perovskite nanocrystals by post-synthetic treatment with tin (Ⅱ) bromide

Enhanced photoluminescence quantum yield and stability of CsPbBr3 perovskite nanocrystals by post-synthetic treatment with tin (Ⅱ) bromide

Ionic liquid alkyl chain regulated highly stable and luminescent silica-coated perovskite quantum dots for bright white light-emitting diodes

Silica-coated perovskite quantum dots (QDs), which exhibit exceptional photophysical properties, hold great promise for various optoelectronic applications. Nonetheless, the issue of insufficient stability poses a significant challenge to their continued advancement and widespread adoption. Herein, we present a novel approach for the synthesis of silica-coated CH3NH3PbBr3 (CH3NH3 = MA) QDs with exceptional stability and luminescence, which utilized hydrophobic ionic liquids (ILs) with unlike alkyl chain lengths as surface ligands. As the alkyl chain length of the hydrophobic ILs increased, we observed a blue-shift in the wavelength and a reduction in the time required to reach maximum fluorescence for the silica-coated perovskite QDs. It not only effectively prevents QD aggregation but also accelerates the formation rate of the SiO2 shell. The introduction of ILs generated the enhancement of photoluminescence quantum yield (PLQY) from 85% for the pristine sample to 92.83% for ILs treated C16-QDs@SiO2. Furthermore, the stability of the ILs-treated C16-QDs@SiO2 was notably enhanced, with the fluorescence intensity retaining 80.5% after 40 days of storage. The as-prepared white light emitting diode (LED) displayed a high color rendering index (CRI) of 75.3 and a correlated color temperature (CCT) of 7529 K. This work provides an alternative strategy to solve the challenging stability issue of silica-coated perovskite QDs and promote the silica-coated perovskite QDs to the practical application in solid-state LEDs.

Origin of singlet self-trapped exciton and enhancement of photoluminescence quantum yield of organic–inorganic hybrid antimony(III) chlorides with the [SbCl5]2− units

Origin of singlet self-trapped exciton and enhancement of photoluminescence quantum yield of organic–inorganic hybrid antimony(III) chlorides with the [SbCl5]2− units

Rhenium(I) Complexes with Sulfur-Bridged Dipyridyl Ligands: Structural, Photophysical, and Computational Studies.

A series of six new rhenium(I) tricarbonyl complexes [Re(CO)3(N-N)Br] bearing sulfur-bridged dipyridyl (N-N) ligands with three different oxidation states (sulfide (S), sulfoxide (SO), and sulfone (SO2)) are described. Spectroscopic studies show that changing the oxidation state of the ligands influences the photophysical properties of the complexes, with complexes 3 and 6 containing the sulfone ligand exhibiting a lower energy MLCT absorption band tailing into the visible region. Solution-state emission measurements show that these complexes exhibit readily tunable emission energies from 480 to 610 nm, depending on the oxidation state of the sulfur bridge and the presence of substituents on the pyridyl rings. Solid-state emission measurements show that the emission is significantly red-shifted upon oxidation of the sulfur bridge to sulfone with enhanced photoluminescence quantum yield.

Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

Morphology Transition with Temperature and its Effect on Optical Properties of Colloidal MoS2 Nanostructures.

Morphology plays a crucial role in determining the chemical and optical properties of nanomaterials due to confinement effects. We report the morphology transition of colloidal molybdenum disulfide (MoS2) nanostructures, synthesized by a one-pot heat-up method, from a mix of quantum dots (QDs) and nanosheets to predominantly nanorods by varying the synthesis reaction temperature from 90 to 160 °C. The stoichiometry and composition of the synthesized QDs, nanosheets, and nanorods were quantified to be MoS2 using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. A nanostructure morphology transition due to variation in the reaction temperature resulted in a photoluminescence quantum yield enhancement from 0 to 4.4% on increasing the temperature from 90 to 120 °C. On further increase in the temperature to 160 °C, a decrease in the quantum yield to 3.06% is observed. Red-shifts of ≈18 and ≈140 nm in the emission maxima and absorption edge, respectively, are observed for the synthesized nanostructures with an increase in the reaction temperature from 90 to 160 °C. The change in the quantum yield is attributed to the change in shape and hence confinement of charge carriers. To the best of our knowledge, microscopic analysis of variation in shape and optical properties of colloidal MoS2 nanostructures with temperature, explained by a nonclassical growth mechanism is presented here for the first time.

Temperature-dependent steady-state and time-resolved photoluminescence spectroscopy of CsPbBr3 encapsulated with PbBrOH and PVA

In this work, photoluminescence (PL) intensity and stability of CsPbBr3/PbBrOH powders synthesized by one-pot method are enhanced through the encapsulation of poly (vinyl acetate) (PVA) in water. Understanding the function of PbBrOH and PVA matrix for photogenerated transition can be achieved through temperature-dependent steady-state and time-resolved PL. The enhanced PL quantum yield (65.9%) and longer lifetime indicate the strengthened structural stability and a significant reduction in nonradiative recombination of CsPbBr3. Negative thermal quenching can be observed and interpreted using a multilevel PL transition model. Through nanosecond time-resolved PL spectra under femtosecond laser excitation, it is revealed that the PL position shows a redshift (∼8 nm) with time delay due to the reduction of band-filling effect during the recombination of photoexcited carriers. PVA further encapsulates CsPbBr3/PbBrOH powders to form a flexible film, which exhibits excellent thermal and water stability due to the dual protective effects of PVA and PbBrOH. The experimental investigation demonstrates that CsPbBr3 encapsulated by PbBrOH and PVA possesses excellent luminescent and water-resistant characteristics, making it a new choice for practical applications in LEDs and screen printing.

In-situ synthesis of MAPbBr3 perovskite quantum dot-polycaprolactone composites with enhanced photoluminescence quantum yield and stability

Polymer encapsulation is regarded as an efficient strategy to enhance the stability of perovskite quantum dots (PQDs), and also endows the perovskites with advantages in mechanical properties and processibility. In this work, polymer encapsulation was achieved by in-situ synthesis of PQDs in polycaprolactone (PCL) polymer, which avoiding time-consuming process of blending polymer with PQDs. Moreover, besides of acting as encapsulation matrix, PCL in toluene could provide large nucleation sites for PQDs formation, resulting in the relatively smaller PQDs size and enhanced photoluminescence quantum yield (PLQY) with respect to the composites prepared by physical blending. Profiting from PCL encapsulation, the as-synthesized PQDs-PCL composites exhibited enhanced stability against UV light, water and heat. The strong interaction between PQDs and PCL in composites with high PCL concentration could endow them with more significantly improved PL stability under UV-light illumination and relatively better mechanical properties compared to the composites with high PQDs concentration. This work provides an efficient method to synthesize PQDs-polymer composites with enhanced PLQY and stability, which would promote practical applications of PQDs materials in the optoelectronic applications.

Halide salt-tuning at interface: Highly water-stable and anion-exchange-active CsPbX3@SiO2 Trimurti nanoparticles for multicolor metabolite assay

High water stability and fast anion exchange (FAE) activity are indispensable requirements of CsPbX3 (X = Cl, Br, I) nanoparticles (NPs) for achieving multicolor fluorescence sensing in aqueous samples. In this study, we prove that the crystal phase transition rate from Cs4PbX6 to CsPbX3 can be finely tuned by halide salt, thereby facilitating the exposure of in-situ SiO2 nucleation sites to CsPbX3. Through the sol–gel method triggered by KX-containing water, monodisperse CsPbX3@SiO2 Trimurti nanoparticles (TNPs), i.e., double-side SiO2-coated CsPbX3 NPs, are successfully synthesized for the first time. As an example, the CsPbBr3@SiO2 TNPs exhibit significantly enhanced photoluminescence quantum yield (80%), fluorescence lifetime (22.09 ns) and water stability (only 11.4% drop in FL intensity after 60 min reaction with water), meanwhile maintain consistent high FAE activity, compared to bare CsPbBr3 NPs (57%, 6.56 ns, 97.9% drop) and single-side SiO2-coated NPs (69%, 9.76 ns, 39.1% drop). Furthermore, we propose an H2O2 recognition strategy at the organic/aqueous phase interface based on the FAE effect between oleylammonium iodide (OLAI) and CsPbX3@SiO2 TNPs. Thus, the TNPs-based multicolor sensing platform for small molecule metabolites is constructed and utilized for uric acid detection in serum, which obtains consistent results with the commercial method (relative error ≤ 5.67%). This work not only provides a guidance for the tunable surface modification of high-performance CsPbX3 NPs, but also designs a universal strategy for selectively detecting small molecule metabolites in biological fluids based on the intrinsic FAE effect.

Hybrid Ligand Polymerization for Weakly Confined Lead Halide Perovskite Quantum Dots

Rational ligand passivation is essential to achieve a higher performance of weakly confined lead halide perovskite quantum dots (PQDs) via a mechanism of surface chemistry and/or microstrain. In situ passivation with 3-mercaptopropyltrimethoxysilane (MPTMS) produces CsPbBr3 PQDs with an enhanced photoluminescence quantum yield (PLQY, ΦPL) of up to 99%; meanwhile, charge transport of the PQD film can be enhanced by one order of magnitude. Herein, we examine the effect of the molecular structure of MPTMS as the ligand exchange agent in comparison to octanethiol. Both thiol ligands promote crystal growth of PQDs, inhibit nonradiative recombination, and cause blue-shifted PL, while the silane moiety of MPTMS manipulates surface chemistry and outperforms owing to its unique cross-linking chemistry characterized by FTIR vibrations at 908 and 1641 cm-1. Emergence of the diagnostic vibrations is ascribed to hybrid ligand polymerization arising from the silyl tail group that confers the advantages of narrower size dispersion, lower shell thickness, more static surface binding, and higher moisture resistance. In contrast, the superior electrical property of the thiol-passivated PQDs is mostly determined by the covalent S-Pb bonding on the interface.

Effects of pH on the Structure and Optical Property of Molybdenum Disulfide Nanocrystals Synthesized by Hydrothermal Method

Molybdenum disulphide (MoS2) is emerging as one of the most attractive two-dimensional (2D) materials amongst the transition metal dichalcogenides (TMDs) group. MoS2 exhibits a thickness-dependent band gap that changes from indirect band gap of ~1.3 eV for bulk MoS2 to direct band gap of ~1.9 eV in monolayer form. Such indirect-to-direct gap transition due to quantum confi nement results in giant enhancement in photoluminescence quantum yield. Recent study demonstrated that the co-existence of 2H- and 1T-MoS2 synthesized by hydrothermal method exhibited superior electronic conductivity to those with 2H semiconducting phase. Metallic 1T phase of MoS2 is attracting much attention due to its high electronic conductivity and potential applications in supercapacitors, thermoelectric energy harvesting, and memristors. In this paper, we investigated a hybrid structure between 2H and 1T of MoS2 by a hydrothermal process and investigated its optical property via photoluminescence spectra with changes in pH values. Our results indicated that photoluminescence occurred in the visible light region and the band gap was determined to be ~1.96–2.50 eV. In addition, pH of the precursor solution strongly affected the fi nal structure of MoS2 nanocrystals, which in turn, affected their photoluminescence property wherein pH = 4–5 was identifi ed as optimum for 2H–1T-MoS2 synthesis.