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Efficient charge injection into the emitters, which can reduce the voltage loss at interfaces, is a prerequisite for high-performance light-emitting diodes, with low voltage operation. Here we develop a sol–gel ZnO (s-ZnO) electron-transport layer for the perovskite light-emitting diodes (PeLEDs) with green-emission formamidinium lead bromide (FAPbBr3) perovskites as emitters. Polyethylenimine (PEI) is mixed into the s-ZnO precursor as a modifier, which not only promotes the wettability of s-ZnO films, but also passivates the defects of s-ZnO without sacrificing their electrical conductivity. As a result, highly efficient FAPbBr3 films are obtained on the s-ZnO films. The maximum current efficiency of PeLED with s-ZnO:PEI electron-transporting layer reaches 13.5 cd/A, 45% higher than that based on pristine s-ZnO without PEI modifier. Benefiting from the outstanding charge-transport properties of s-ZnO and high-quality perovskite film, the turn-on voltage of the s-ZnO based PeLEDs is only 1.9 V, much lower than the band-gap voltage (~ 2.3 V) of FAPbBr3. [ABSTRACT FROM AUTHOR]

As one of Cd-free semiconductor nanocrystals, Zn-based nanocrystals are widely studied due to their wide band gap to be a candidate for blue- and green-emitting materials. Herein, ZnInGaSe nanocrystals were synthesized with the controlled stoichiometry from the intermediate of ZnInGaSe magic size clusters. The approach via the magic size clusters greatly increases the amount of Ga in ZnInGaSe NCs. After the growth of the ZnS shell, ZnInGaSe/ZnS core/shell nanocrystals exhibited improved green emission. Furthermore, Cu as the impurity was introduced into ZnInGaSe NCs to reduce the vacancy defects to promote the photoluminescence. Finally, a photoluminescence quantum yield of 35.7% was obtained in Cu:ZnInGaSe/ZnS core/shell nanocrystals. The donor–acceptor recombination mechanism was proposed to explain the optical properties in ZnInGaSe NCs. Cu:ZnInGaSe nanocrystals were utilized in light-emitting diodes, showing the potential of ZnInGaSe nanocrystals for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Herein, a novel molecular SO2‐Bri‐DSB based on the sulfone‐bridged distyrylbenzene derivative is synthesized, and its organic crystal is fabricated. It has a very high photoluminescence (PL) quantum efficiency in the solution and crystalline state, i.e., dual‐state emission (DSE), and the corresponding PL mechanism is clarified in detail using the transient absorption and transient PL test. The PL behaviors in the monomolecular state and organic crystal are compared. In addition, the optical anisotropy of the SO2‐Bri‐DSB crystal is thoroughly investigated using various polarization‐dependent spectroscopy techniques. The time evolution of anisotropy is composed of a step behavior caused by the anisotropy of the electronic transition and a slow enhancing process with a lifetime of 4.86 ns, which is governed by the change in emission lifetime due to the anisotropy. The space‐resolved evolution of the optical anisotropy is investigated using the polarization‐dependent light wave‐guiding test and exhibits that the emission anisotropy gradually decreases with length, and it has a longer effective propagation length than the polarization emission signal. The findings provide insight into the intrinsic optical anisotropy of single‐molecular crystals and indicate that these materials have enormous potential in the domains of polarization lighting and display. [ABSTRACT FROM AUTHOR]

Currently, the performance of quantum‐dot light‐emitting diodes (QLEDs) based on environmental‐friendly Cu─In─Zn─S quantum dots (QDs) still lags far behind that of Cd‐QDs‐based devices. Here it is demonstrated that the unique trap‐related recombination in Cu─In─Zn─S QDs is mainly responsible for the low device efficiency. The luminous efficiency of Cu─In─Zn─S‐based QLEDs is rather sensitive to the temperature and hole‐transporting layers (HTLs) due to the susceptible thermal‐related trappingdetrapping processes of holes in radiative Cu‐related traps. The holes in Cu‐related traps can be quenched by escaping to the valence band of the QDs or/and transferring to the adjacent HTLs. An HTL with low highest occupied molecular orbitals is desired to enhance the hole injection and hinder the aforementioned hole transfer. As a result, a high device efficiency of 6.0 cd A−1 is achieved at room temperature, which is attributed to suppressed HTL‐induced emission quenching and efficient valence‐band‐dominated hole injection from HTL to the QDs. The device efficiency is further increased to 13.2 cd A−1 at 150K by suppressing thermal‐induced quenching. [ABSTRACT FROM AUTHOR]

A clear understanding on the fundamental working mechanisms of quantum‐dot light emitting diodes (QLEDs), especially the blue devices, is always sought after. Here the electroluminescence (EL) turn‐on mechanism of blue QLEDs is unraveled by structure engineering of the hole‐transport layers (HTLs). It is demonstrated that the EL turn‐on in blue QLEDs is highly dependent on the charge‐transport polarity of the HTLs. Energy transfer between HTLs and the blue quantum dots (QDs) occurs for the QLEDs based on bipolar HTLs, and, in contrast, charge injection is responsible for EL turn‐on of the blue devices consisting of unipolar HTLs. In addition, large hole‐injection barrier results in serious accumulation of holes at the interface of HTLs/QDs, then inducing serious electrons leakage into the HTLs, thereby leading to poor device efficiency under low driving current. It is suggested here that confining the carriers to the quantum dots and reducing the hole‐injection barrier remain two critical aspects to optimize the performance of blue QLEDs. [ABSTRACT FROM AUTHOR]

Inorganic semiconductor nanocrystals (NCs) are considered potential emitters for next-generation displays due to their special quantum size confinement effect. Herein, Cd-free AgInZnS (AIZS) NCs were produced via the cation exchange reaction from AgIn5S8 NCs for light-emitting diodes as green emitters. AIZS NC-based light-emitting diodes showed a maximum current efficiency of 6.34 cd/A and an external quantum efficiency of 1.3%, which are the highest values for AIZS NC-based light-emitting diodes for green emitters so far. The composition of AIZS NCs produced with different ligands can vary the band gap structure of AIZS NCs, affecting the balance of charge injections in the device to induce different performances of AIZS NC-based light-emitting diodes. [ABSTRACT FROM AUTHOR]

In order to improve the optoelectronic performance of π-conjugated molecules with electronic donors and electronic acceptors, people often choose multi-branch molecule structures, which can enhance the charge transfer ability. In this work, the photo-physical characteristics of (E)-4-(2-(3-methylquinoxalin-2-yl)vinyl)-N,N-diphenylaniline (QTPA1) and 4,4′-((1E,1′E)-quinoxaline-2,3-diylbis(ethene-2,1-diyl))bis(N,N-diphenylaniline) (QTPA2) in monodisperse systems and aggregated states were investigated in detail, showing that the photoluminescence quantum yield (PLQY) of oligomers is apparently enhanced in high-polarity solutions and decreased in low-polarity solvents instead, after the oligomer is linked with a conjugated branch. Based on the pump–probe and pump–dump–probe, this unusual phenomenon is assigned to the polarity-dependent intramolecular charge transfer (CT) mechanism of oligomers induced by the conjugated branch. In the PL of aggregated state and the two-photon fluorescence (TPF), increasing the conjugated branch has a positive effect on the PL characteristics that the PL performance of QTPA2 is higher than that of the aggregated QTPA1. In the aggregated state, QTPA2 has a larger degree of π electron conjugation, which suppresses intramolecular vibrations and reduces the energy loss caused by non-radiative processes. In addition, the two-photon absorption section of QTPA2 keeps higher in comparison with that of QTPA1 owing to the enhancement of the intramolecular dipole intensity, leading to the enhancement of TPF. This research could elucidate the physical mechanism underlying the optoelectronic performance and help us develop novel organic optoelectronic materials with high performance. [ABSTRACT FROM AUTHOR]

Currently, blue quantum‐dot light‐emitting diodes (QLEDs) remain the bottleneck limiting the development of QLED‐based applications. To achieve high‐performance blue QLEDs, poly‐N‐vinylcarbazole (PVK) is usually employed as the hole‐transport layer (HTL) to reduce the hole injection barrier. However, fabrication of efficient blue QLEDs with PVK HTL remains challenging and empirical/accidental. Here, it is demonstrated that PVK layer can trap electrons and hence resulting in low device efficiency. This is why the performance of blue QLEDs is highly dependent on the PVK batch received from the manufacturers. As an interlayer, ZnSe/ZnS quantum dots (QDs) are inserted between PVK and blue ZnCdSe/ZnS QD emitters. The resulted device presents an external quantum efficiency of 20.6% under 2920 cd m−2, enhanced by ≈35% compared with that of PVK‐alone device. The remarkable enhancement is owing to the QD interlayer that not only suppresses the electron trapping in PVK, increasing the probability of exciton recombination within the emissive layer, but also facilitates the hole injection, improving the charge balance in blue devices. [ABSTRACT FROM AUTHOR]

Although huge progress has been made for quantum-dot light-emitting diodes (QLEDs), blue devices remain a short slab limiting the development of QLED based applications. For blue devices, a fundamental and key question—how the shell thickness affects the charge injection—remains unclear by far. Herein, we show a comprehensive investigation on the effect of shell thickness on the charge injection by employing blue CdxZn1−xSeyS1−y/ZnS core/shell QDs with various shell thicknesses as the emission layers. We demonstrate that, during the electroluminescence onset processes, the fast and slow components of the rising edges characterized by transient electroluminescence spectra are strongly associated with the electron and hole injection processes, respectively. We find that the shell thickness influences the injection of electrons more dramatically than that of holes. A thick shell suppresses the electron injection and consequently reaches a more balanced charge injection into QDs, hence leading to an enhanced efficiency. [ABSTRACT FROM AUTHOR]

Organic molecules with hybridized local and charge transfer (HLCT) characters have attracted attention because of their potential in the field of two-photon fluorescence imaging and light-emitting diodes (LEDs). Herein, the 4-(1,1-difluoro-1H-1λ4,10λ4-benzo[4,5]thiazolo[3,2-c][1,3,2]oxazaborinin-3-yl)-N,N-diphenylaniline (TOND) molecule is studied through various spectroscopy tests to explore the solvent-dependent photo-physical properties in the mono-disperse system and temperature-dependent photoluminescence behavior in the aggregation state system. The monodisperse TOND shows apparent two-photon fluorescence properties and its absorption section enhances with solvent polarity owing to the intramolecular charge transfer (ICT) process. The solvent-dependent relaxation process of excited TOND, which is affected by the ICT process, is analyzed by pump–probe and pump–dump–probe tests. The aggregated TOND can be fabricated into an LED, whose emission peak is centered at 566 nm with the Commission Internationale de l'Eclairage chromaticity (CIE) coordinates of (0.47, 0.51). Their radiative lifetime and photoluminescence quantum yield together decrease with increasing temperature, due to the activation of the non-radiative process at high temperatures. Our results provide a comprehensive insight into the optoelectronic properties of these organic molecules. [ABSTRACT FROM AUTHOR]

2D transition metal dichalcogenides (TMDCs) nanocrystals and related semiconductor–metal heterostructures are promising new materials for efficient opto-electrical conversion because of their unique physical and chemical properties. The design and optimization of such materials require the understanding of exciton and charge carrier dynamics. The illumination-dependent carrier dynamics of CdS/MoS2 heterostructure nanocrystals (CdS/MoS2 HNCs) film is investigated by employing the voltage-current test, in which the CdS nanocrystals (NCs) film is used as a reference. The photocurrent performance of carriers in the CdS/MoS2 HNCs is 70 times higher than that in CdS NC film, owing to the excellent interfacial hole transfer from the CdS component to the monolayer MoS2 in CdS/MoS2 HNCs, which effectively reduces the bulk and surface charger recombination. It means that the remaining electron in CdS component after hole transfer plays an important role in the final photocurrent performance. The annealing effect also plays a positive role in the photocurrent performance of nanocrystal film for CdS/MoS2 HNC and CdS NC film. In addition, the transient absorption test is also used to exclude the possibility of interfacial electron transfer. The final results suggest that the construction of nano-heterojunction can affect the carrier dynamics of nanomaterials and enhance light responsiveness, which is conductive to the design and application of photovoltaic devices in the future. [ABSTRACT FROM AUTHOR]

The photon flux-dependent transient absorption spectroscopy is employed to investigate the carrier dynamics of Cs2AgBiBr6 nanocrystals (NCs), exhibiting that the hot carrier cooling, the self-trapping process, the surface defect capture and the carrier recombination together participate in the carrier relaxation process after photoexcitation. The evolution of their lifetimes as a function of 〈N〉 (average photon number per nanocrystal) all show two stages. Moreover, the role of HC in the subsequent carrier dynamics is also discussed. These results can help explain the carrier dynamics in the double perovskite NCs for designing and optimizing the perovskite-based optoelectronic devices with high performance. [ABSTRACT FROM AUTHOR]

Quantum dot-based light-emitting diodes (QLEDs) have been considered as a highly promising candidate for lighting and display applications. Their peak external quantum efficiencies (EQEs) are now approaching the theoretical values for red/green/blue QLEDs. However, these peak values are commonly obtained at low current densities (low brightness), whereas their efficiency usually exhibits a quick roll-off with increasing current densities, especially for blue QLEDs, limiting the operation lifetime and applications. In this study, we demonstrated suppressed efficiency roll-off and bright blue QLEDs by using propanethiol-modified ZnCdSeS QDs as the emitters. A peak EQE of 9.9% is achieved at a luminance of 1040 cd m−2, along with a high luminance up to 52 360 cd m−2. Moreover, the reduction of the EQE is less than 50% of the peak value until the luminance is as high as 28 260 cd m−2, highly superior to the control device. Most importantly, higher than 75% of the peak EQE value is sustained within the luminance range from 100 to 10 000 cd m−2, which has already reached the threshold values for applications in both displays and lighting. We attribute these major advances to the transport-enhancement of short-chain ligands outside the QDs, which improves both conductivity and injection balance of the emissive layer, reducing the quenching processes induced by accumulated charges. [ABSTRACT FROM AUTHOR]

Quantum dot light emitting diodes (QLEDs) have been emerging with unique photoelectrical properties and their efficiency is rapidly approaching the commercialization requirement. However, the device operation lifetime is still one of the biggest obstacles facing the QLED applications. Here, we investigate the case of degradation of red QLEDs by a low driving level (7.5 mA cm−2) because devices can commonly achieve a luminance of ∼500–2000 cd m−2 (that is required in display applications) under this driving current. Based on the photoelectrical characteristics of QLEDs with different aging times, we find that the device stability is dominantly affected by the interfaces between QDs and adjacent charge transport layers. Some of the QDs stay in the permanent dark states (lightless states) due to the aging process, which may result from the generation of nonradiative sites in the hole-transport layer (HTL). The electron leakage should be responsible for the degradation of the HTL, leading to a highly resistive HTL and the rise of the operation voltage for the aged devices. Therefore, suppressing the interactions between QDs and charge transport layers and confining the charges within the QDs are feasible ways to boost the operation stability of QLEDs. [ABSTRACT FROM AUTHOR]

Time‐resolved coherent anti‐Stokes Raman spectroscopy can disentangle the exciton energy dissipation (EED) dynamics of the intrachain exciton in conjugated polymers (MEH‐PPV) coupled with several phonon modes and the corresponding phonon relaxation dynamics by adjusting the timing between lasers in the coherent anti‐Stokes Raman spectroscopy system. The intrachain EED process is coupled with phonon modes located at 966; 1118; 1283; and 1560 cm−1, respectively. Of these, the phonon mode at 966 cm−1 corresponds to the out‐of‐plane CH bending vibration in the vinylene group. This is the primary channel for EED because the vinylene group is close to the conjugated unit and the corresponding chemical bond is flexible. After annihilation of the intrachain exciton, some excess energy from MEH‐PPV in the ground state would further dissipate via energy redistribution between phonon modes at 1283 and 1118 cm−1, ultimately leading to phonon relaxation. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite quantum dots (QDs) with high photoluminescence quantum yield, narrow spectral bandwidth, and broad spectral tunability have broad applications. However, perovskite QDs suffer from poor stability and the fast anion‐exchange reaction between different halide ions. Herein, we embedded green‐light‐emitting CsPbBr3 QDs and red‐light‐emitting CsPb(Br/I)3 QDs into carboxyl‐containing polymethyl methacrylate (PMMA) by the hot‐injection method. As a result, the as‐prepared perovskite@PMMA composites not only retain high luminescence but also exhibit good water resistance. Moreover, this treatment prevents anion exchange between different halide QD particles in the solid state. The applications in light‐emitting diodes and cellular labeling agents are also carried out to demonstrate their good stability. Waterproof particles: CsPbBr3 particles were successfully encapsulated into carboxyl‐containing PMMA and exhibited good stability in water. The water resistance of 500 nm CsPbBr3@PMMA composites was tested (figure shows photographs of the composites water solution under daylight and UV light). The relative PL emission intensity decreased very slowly over time, retaining 90% of its original value after 12 h exposure to water. [ABSTRACT FROM AUTHOR]

During the last three decades, there has been significant development of quantum dot light emitting diodes (QLEDs) due to their widespread applications. However, common QLEDs depend on cadmium, which is toxic and limits their all-inclusive applications. To address this challenge, herein, we report a highly efficient and low turn-on voltage Cd-free inverted QLEDs with eco-friendly Zn–Ag–In–S quantum dots as the emissive layers. The device performance is closely related to the properties of the hole transport layer (HTL), which are explored by employing different hole transport materials, namely, 4,4′,4′′-tris(carbazol-9-yl) triphenylamine (TCTA) and N,N′-bis(naphthalen-1-yl)-N,N′ bis(phenyl)-benzidine (NPB). Although the energy levels of the lowest unoccupied molecular orbitals (LUMO) of TCTA and NPB are similar, electron leakage from the QDs to NPB is observed, which deteriorates the device performance. An excellent QLED can be achieved if a thick TCTA layer is introduced next to the QDs. Additionally, the QLED with a stepwise HTL consisting of TCTA/NPB presents a slightly higher current efficiency than the TCTA-only device, revealing that the reduction in holes accumulated at the QDs/HTL interface is beneficial for enhancing the device efficiency. Compared to the previously reported Zn–Ag–In–S based QLEDs, our device exhibits a low turn-on voltage of 2.2 V and the highest luminance (over 2000 cd m−2) and efficiency (larger than 2.1 cd A−1). [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) have attracted extensive attention over the past decade due to their excellent advantages. However, few attempts have been reported for realizing the long-wavelength emission, especially for obtaining efficient solid-state red emission with high photoluminescence quantum yield (QY). Herein, we developed highly red light emitting CDs by the step-by-step surface modifications of the nitrogen-doped CDs. By introducing hexadecyltrimethyl ammonium bromide to modulate a red CD aqueous solution, the photoluminescence QY increases from 23.2% to 43.6%. Furthermore, we dispersed CDs in a PVP matrix for a solid-state film, where the solid-state quenching was effectively suppressed, and high QY (41.3%) of red light emission was achieved. Taking advantage of the as-prepared red light emitting CDs combining with the reported high quantum yield blue and green light emitting CDs, we realized UV-pumped WLEDs with tunable correlated color temperature from 7879 to 2961 K. Moreover, a high color rendering index (CRI) of 93 for WLEDs was realized, which is superior than the best records for the semiconductor quantum dot based WLEDs. Finally, the red light emitting CDs were demonstrated to have promising application as a red color converter in traditional YAG-based WLEDs to improve their CCT and CRI. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) exhibit excellent ultraviolet (UV) absorption and tunable photoluminescence over the full visible light range, which endows CDs with huge potential to be designed as efficient full-color emitting phosphors for UV to white light conversion. However, the low quantum yield (QY) for white light emission and solid-state quenching dramatically limit their optoelectronic applications. We proposed an effective strategy for modulating the emitting states of colloidal CDs by introducing hexadecyltrimethyl ammonium bromide. Consequently, white light emission with tunable correlated color temperature from 8121 K to 3623 K was realized. Furthermore, we dispersed CDs in a PVP matrix for solid-state films, where the solid-state quenching was effectively avoided. A white light-emitting QY of 38.7% was thus achieved through the inhibition of non-radiative electron–hole recombination as well as the cooperation between the intrinsic state of the carbogenic cores and the surface-related state of the organic ligands. The white light emitting QY is much higher than that of other reported CDs (ca. 15% in the soluble state and not reported in the solid-state) and is comparable to that of the nanophosphors with the highest UV pumped single-component white light emissions reported in the literature. [ABSTRACT FROM AUTHOR]

Flexible quantum dot light emitting diodes (QLEDs) are highly desired due to their advantages of foldability, lightweight, and potential applications in lighting and displays. In this report, we successfully fabricated high performance red (R), green (G), and blue (B) three primary color QLEDs based on a poly(ethylene-terephthalate)/ITO/Ag/ITO (PET–IAI) cathode. The multilayer flexible IAI electrode shows outstanding stability even after bending over 2000 times with a critical bending radius of 5 mm; the sheet resistance of the IAI film only increases from 12.7 to 14.8 Ω□−1. The maximum current efficiencies are 16.3, 86.5, and 16.1 cd A−1 for RGB QLEDs, respectively, which is the best device performance for flexible RGB QLEDs reported to date. Moreover, to the best of our knowledge, these are also record efficiencies for the green and blue devices in all the reported QLEDs. Furthermore, all the devices show saturated electroluminescence (EL) with the corresponding emission peaks at 606, 530, and 478 nm for three primary color QLEDs. The superior performance is a result of high transmittance and stability of the PET–IAI film. These results signify remarkable progress in flexible QLEDs and suggest that the PET–IAI based flexible QLEDs can offer a practicable platform for foldable applications. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) were fabricated by employing a combination of a commercial yellow emission Ce-doped YAlO (YAG:Ce)-based phosphor and all-inorganic perovskite quantum dots pumped with blue LED chip. Perovskite quantum dot solution was used as the color conversion layer with liquid-type structure. Red-emitting materials based on cesium lead halide (CsPb(X)) perovskite quantum dots were introduced to generate WLEDs with high efficacy and high color rendering index through compensating the red emission of the YAG:Ce phosphor-based commercialized WLEDs. The experimental results suggested that the luminous efficiency and color rendering index of the as-prepared WLED device could reach up to 84.7 lm/W and 89, respectively. The characteristics of those devices including correlated color temperature (CCT), color rendering index (CRI), and color coordinates were observed under different forward currents. The as-fabricated warm WLEDs showed excellent color stability against the increasing current, while the color coordinates shifted slightly from (0.3837, 0.3635) at 20 mA to (0.3772, 0.3592) at 120 mA and color temperature tuned from 3803 to 3953 K. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) characteristics of semiconductor CdSe quantum dots (QDs) aggregated on Cu nanowires (NWs) were studied in detail. The PL relaxation dynamic data show that Cu NWs improve the PL intensity of CdSe QDs by accelerating the emission relaxation rate. The temperature-dependent PL data and excitation intensity-dependent PL data suggest that the activation energy of CdSe QDs might decrease due to the excellent heat transfer properties and the plasmon effect of Cu NWs. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) characteristics of MEH-PPV hybrid films blended with Au nanoparticles are studied in detail. Due to the strong coupling effect between the surface plasmon of Au nanoparticles and the emission of MEH-PPV, the introduction of Au nanoparticles could enhance the PL intensity and modulate the shape of absorption and excitation spectra, according to our steady spectroscopy experiments. Besides, the relaxation dynamic experiments show that the non-radiative rate in the hybrid system decreases. The temperature and the excitation intensity (EI)-dependent PL spectral data indicate that hybrid MEH-PPV films have lower activation energy and higher thermal exchange rate. As a result, the thermal accumulation effect and the non-linearity of EI-induced PL enhancement are suppressed in hybrid films. [ABSTRACT FROM AUTHOR]

ABSTRACT The effect of the photonic stop bands (PSBs) on the spontaneous emission from tris(8-hydroxyquinolinato)aluminum (Alq3) doped in the beads of polymethylmethacrylate opal photonic crystals (PCs) is investigated in detail. The structure of PSBs in PCs has been analyzed. The steady emission data exhibits that the first- and second-order PSB could effectively influence the spectral characteristics of Alq3 through changing the incident angles. The emission dynamic data is also investigated by using the Kohlrausch strengthened exponential model, which shows that the emission decay rate of Alq3 can be decelerated as the PSB of PC approaches the emission peak of Alq3. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 842-847 [ABSTRACT FROM AUTHOR]

We have studied the optical properties of PbSe colloidal quantum dot-solution filled hollow core multimode silica waveguides as a function of quantum dot-solution concentration, waveguide length, optical pump power and choice of organic solvent in order to establish the conditions to maximize near infrared spontaneous emission intensities. The optical performance was compared and showed good agreement with a simple three level system model for the quantum dots confined in an optical waveguide. Near infrared absorption-free solvent of tetrachlorethylene was confirmed to be a good candidate for the waveguide medium due to the enhancement of output intensity from the liquid-core fiber compared to the performance in toluene-based fiber. This approach demonstrates a useful method for early characterization of quantum dot materials in a waveguide test-bed with minimal material processing on the colloidal nanoparticles. [ABSTRACT FROM AUTHOR]

A theoretical model was established in this paper to analyze the properties of 3.50 and 4.39 nm PbSe quantum dot-doped liquid-core multi-mode fiber. This model was applicable to both single- and multi-mode fiber. The three-level system-based light-propagation equations and rate equations were used to calculate the guided spontaneous emission spectra. Considering the multi-mode in the fiber, the normalized intensity distribution of transversal model was improved and simplified. The detailed calculating results were thus obtained and explained using the above-mentioned model. The redshift of the peak position and the evolution of the emission power were observed and analyzed considering the influence of the fiber length, fiber diameter, doping concentration, and the pump power. The redshift increased with the increases of fiber length, fiber diameter, and doping concentration. The optimal fiber length, fiber diameter, and doping concentration were analyzed and confirmed, and the related spontaneous emission power was obtained. Besides, the normalized emission intensity increased with the increase of pump power in a nearly linear way. The calculating results fitted well to the experimental data. [ABSTRACT FROM AUTHOR]

Here, we present strong modification of photonic crystals on the spontaneous emissions of Eu3+ ions in YVO4:Eu3+ inverse opal. It is interesting that due to the effect of local field, the 5D0-7FJ radiative lifetimes of Eu3+ ions in the PCs are all prolonged ∼2.5 times in contrast to the grinded reference (REF) in air, consistent with the empty cavity model. The photonic stop band and the radiative lifetime are both highly sensitive to the refractive index of the infiltrated solutions, in accordance with the real cavity model. [ABSTRACT FROM AUTHOR]

The absorption of a weak probe beam for a V-type atom with a closely spaced doublet is studied under conditions such that vacuum-induced interference among decay channels is important. It is shown how the probe polarization as well as the vacuum-induced interference influence the absorption amplitude and spectral structure. Comparing with similar models studied earlier, where probe polarization direction has not been taken into account, the present study shows that probe polarization has significant effects on the absorption spectra. [ABSTRACT FROM AUTHOR]

A seeded growth method to produce colloidal carbon dots (CDs) through controlling the number of seeds and reaction time, which is demonstrated to be an effective way to tune their optical properties, is developed. Color‐tunable fluorescence of CDs with blue, green, yellow, and orange emissions under UV excitation is achieved by increasing the size of the seed CDs, with the color depending on the size of the π‐conjugated domains. Strong multicolor photoluminescence of powdered samples enables realization of efficient down‐conversion white‐light‐emitting devices with correlated color temperature ranging from 9579 to 2752 K and luminous efficacy from 19 to 51 lm W−1. Moreover, color‐tunable room‐temperature phosphorescence of CD powders is demonstrated in the broad spectral range of 500–600 nm. It is related to the presence of the nitrogen‐containing groups at the surface of CDs, which form interparticle hydrogen bonds to protect the CD triplet states from quenching, and to the existence of the polyvinylpyrrolidone polymer chains at the surface of CDs. The color‐tunable room‐temperature phosphorescence from CDs demonstrated in this work exhibits potential for data encryption. [ABSTRACT FROM AUTHOR]

In this study, the enhanced device performance of CuInS2/ZnS quantum dots‐based light‐emitting didoes (QLEDs) for photomedical applications using polyethylenimine ethoxylated (PEIE)‐modified ZnO as electron transport layer has been reported. The device enhancement is investigated by applying time‐resolved photoluminescence and transient electroluminescence spectra. The results show that the modification of PEIE on ZnO layer limits the electron injection into quantum dots layer and reduces the accumulation of electrons at ZnO/QD interface. This provides an effective way to suppress the charging processes of quantum dots and thus enhance the device efficiency. As a result, the synergistic effect of PEIE modifying layer leads to a record current efficiency of 2.75 cd A−1 for the CuInS2/ZnS‐based QLEDs with deep red emission at 650 nm. [ABSTRACT FROM AUTHOR]

The upconversion luminescence (UCL) for YVO4:Yb3+,Ln3+ (Ln3+ = Er3+, Tm3+, or Ho3+) compounds exhibited novel and intense white light ranging from 400 to 850 nm, and super-broad infrared (IR) bands extending from 1100–1700 nm. The upconversion (UC) populating mechanism was discussed. The discovery described in this paper may be significant for developing novel devices for lighting and display, as well as broad IR optical communications. [ABSTRACT FROM AUTHOR]