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Three A-π-A or D-π-D perylene diimide (PDI) derivatives with varied groups on π-conjugate were synthesized and characterized. The photophysical properties of these compounds were systematically studied by spectral experiments and density functional theory calculations. All compounds displayed intense absorption bands at 300-800 nm wavelengths. However, diverse groups on the π-conjugate influenced the UV-vis absorption. Electron-withdrawing groups on PDI-2 caused a slight red shift at the 350-400 nm wavelength and a blue shift after 400 nm wavelength. At the same time, the electron-donating substituents on PDI-3 caused an obvious red shift of this band. These PDI derivatives exhibited emission in solution at room temperature (λem = 500-850 nm). The quantum yield of PDI-3 decreased, while the electron-donating substituents were introduced to the π-conjugated motifs. However, the quantum yield of PDI-2 increased when electron-withdrawing substituents were introduced to the π-conjugated motifs. In addition, PDI-1 and PDI-2 exhibited broad triplet transient absorption in the visible region. These photophysical properties could help us to understand the relationship between structure and photophysical properties of perylene diimide derivatives and exploit more original perylene diimide-based optical functional materials.

The concept of doping Mn2+ ions into II–VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+‐related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of Ruddlesden–Popper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single‐crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively., The doping of Mn2+ ions into CsPbCl3 nanocrystals (NCs) strongly influences the excitonic properties of the host NCs. Manganese doping leads to the formation of Ruddlesden–Popper defects and thus induces quantum confinement within individual crystals. This results in a blue shift of the excitonic emission.

[EN] The effect of uniaxial strain on the band structure of ZrSe3 , a semiconducting material with a marked in-plane structural anisotropy, is studied. By using a modified three-point bending test apparatus, thin ZrSe3 flakes are subjected to uniaxial strain along different crystalline orientations monitoring the effect of strain on their optical properties through micro-reflectance spectroscopy. The obtained spectra show excitonic features that blueshift upon uniaxial tension. This shift is strongly dependent on the direction along which the strain is being applied. When the flakes are strained along the b-axis, the exciton peak shifts at 60-95 meV %-1 , while along the a-axis, the shift only reaches 0-15 meV %-1 . Ab initio calculations are conducted to study the influence of uniaxial strain, applied along different crystal directions, on the band structure and reflectance spectra of ZrSe3 , exhibiting a remarkable agreement with the experimental results. his project was funded from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 755655, ERC-StG 2017 project 2D-TOPSENSE). R.F. acknowledges the support from the Spanish Ministry of Economy, Industry and Competitiveness through a Juan de la Cierva-formación fellowship 2017 FJCI2017-32919. R.D. acknowledges the financial support of the Grupos Consolidados del Gobierno Basco (Grant IT1249-19) and the MINECO (Grant G17/A01). G.S.-S. acknowledges financial support from Spanish MICIU RTI2018-099054-J-I00 and MICINN IJC2018-038164-I. Electron microscopy observations were carried out at the Centro Nacional de Microscopia Electronica, CNME-UCM. R.D. also acknowledges useful discussions with D. Varsano. H.L. acknowledges the grant from China Scholarship Council (CSC) under no. 201907040070. The authors extend their sincere appreciation to the Distinguished Scientist Fellowship Program (DSFP) at King Saud University for funding of this work.

Understanding the origin of temperature‐dependent bandgap in inorganic lead‐halide perovskites is essential and important for their applications in photovoltaics and optoelectronics. Herein, it is found that the temperature dependence of bandgap in CsPbBr3 perovskites is variable with material dimensionality. In contrast to the monotonous redshift ordinarily observed in bulk‐like CsPbBr3 nanocrystals (NCs), the bandgap of 2D CsPbBr3 nanoplatelets (NPLs) exhibits an initial blueshift then redshift trend with decreasing temperature (290–10 K). The Bose–Einstein two‐oscillator modeling manifests that the blueshift‐redshift crossover of bandgap in the NPLs is attributed to the significantly larger weight of contribution from electron‐optical phonon interaction to the bandgap renormalization in the NPLs than in the NCs. These new findings may gain deep insights into the origin of bandgap shift with temperature for both fundamentals and applications of perovskite semiconductor materials., The temperature dependence of bandgap in inorganic lead‐halide perovskites is found to be variable with material dimensionality. In sharp contrast to the monotonous redshift usually observed in quasi‐3D bulk‐like CsPbBr3 nanocrystals (NCs), the bandgap of 2D 2‐monolayer‐thick (2‐ML‐thick) CsPbBr3 nanoplatelets (NPLs) exhibits an initial blueshift then redshift trend with decreasing temperature (290–10 K).

Europium ion (Eu2+ )-doped phosphors exhibit adjustable photoluminescence due to the sensitivity of their luminescence to the local environment. It is of great significance to adjust the luminescence of Eu2+ by changing their local environment in the host. In this work, we investigated the effect of strontium/barium (Sr:Ba) ratio on the structure and luminescence properties of Sr2-x Bax MgAl22 O36 :Eu2+ phosphors. Our investigation indicates that with the decrease of Sr:Ba ratio, the matrix lattice gradually expands and the peak wavelength for the luminescence of Eu2+ presents an obvious blue shift. The occupancy of Eu2+ was analyzed and the reason for the blue shift was explained. Thermal stability for the luminescence of Eu2+ can also be adjusted by changing the Sr:Ba ratio. This work has a positive effect on the regulation of the emission of phosphors and the improvement of thermal stability, which will promote the application of Sr2-x Bax MgAl22 O36 :Eu2+ phosphors in the field of white light emitting diodes.

Twisted intramolecular charge-transfer (TICT) chromophores exhibit extraordinary hyperpolarizabilities, β, and are therefore promising for electro-optic technologies. Nevertheless, centrosymmetric aggregate formation severely diminishes β in concentrated solutions or in polymer matrices. Herein, the remarkable effects of organic salts on the linear and nonlinear optical response of a high β benzimidazolium-based TICT chromophore, B2TMC-2, are reported. Addition of Bu4 P+ Br- to B2TMC-2 solution in CHCl3 induces a halochromic blueshift, primarily reflecting interactions between Bu4 P+ Br- and the B2TMC-2 cationic portion. DC electric-field induced second-harmonic generation (EFISH) measurements on B2TMC-2+Bu4 P+ Br- solution reveal a large μβ=-22,160×10-48 esu, unprecedented for any chromophore with such a broad optical transparency window. Moreover, Bu4 P+ Br- is shown to suppress B2TMC-2 aggregation, thereby preserving high μβ in concentrated solutions. This phenomenon should be applicable to many other NLO chromophores.

A series of blue-emissive 7-(diphenylamino)-4-phenoxycoumarin derivatives bearing -CF3 , -OMe, or -N(Me)2 substituents on the phenoxy subunit were synthesized. Although both the -CF3 and -N(Me)2 modifications were found to trigger redshifted fluorescence, the -OMe substitution was demonstrated to exert an unexpected blueshift color-tuning effect toward the deep-blue region. The reason is that the moderate electron-donating -OMe group can endow coumarins with unaltered HOMO but elevated LUMO energy levels. Moreover, the -OMe substitution was found to be beneficial to the thermal stability of these coumarins. Therefore, the trimethoxy-substituted objective compound can act as a high-performance deep-blue organic light-emitting diode (OLED) emitter, and OLED based on it emits deep-blue light with CIE coordinates of (0.148, 0.084), maximum luminance of 7800 cd m-2 , and maximum external quantum efficiency of 5.1 %. These results not only shed light on the molecular design strategy for high-performance deep-blue OLED emitters through color-tuning, but also show the perspective of coumarin derivatives as deep-blue OLED emitters.

The introduction of heavy atoms into conjugated molecules often induces a redshift in the emission spectra. Conversely, we report here a blueshifting effect in the absorption and emission bands of a conjugated organic dye by employing a heavier atom from the same element group. Boron complexes having oxygen- and sulfur-bridged structures in the ligand moiety were synthesized, and their optical properties were compared. Significant optical bands in the absorption and luminescence spectra of the sulfur-bridged complex were observed in a shorter wavelength region than those of the oxygen-bridged complex. Theoretical calculations suggest that replacement of the bridging atom by a heavier one should reduce molecular planarity because of the larger atom size. As a result, the degree of electronic conjugation decreases, and this is followed by a blueshift in the optical bands. Finally, a blue-emissive crystal is demonstrated.

New Lennard-Jones parameters have been developed to describe the interactions between atomistic model of graphene, represented by REBO potential, and five commonly used all-atom water models, namely SPC, SPC/E, SPC/Fw, SPC/Fd, and TIP3P/Fs by employing particle swarm optimization (PSO) method. These new parameters were optimized to reproduce the macroscopic contact angle of water on a graphene sheet. The calculated line tension was in the order of 10-11 J/m for the droplets of all water models. Our molecular dynamics simulations indicate the preferential orientation of water molecules near graphene-water interface with one OH bond pointing toward the graphene surface. Detailed analysis of simulation trajectories reveals the presence of water molecules with ≤∼1, ∼2, and ∼4 hydrogen bonds at the surface of air-water interface, graphene-water interface, and bulk region of the water droplet, respectively. Presence of water molecules with ≤∼1 and ∼2 hydrogen bonds suggest the existence of water clusters of different sizes at these interfaces. The trends observed in the libration, bending, and stretching bands of the vibrational spectra are closely associated with these structural features of water. The inhomogeneity in hydrogen bond network of water at the air-water and graphene-water interface is manifested by broadening of the peaks in the libration band for water present at these interfaces. The stretching band for the molecules in water droplet shows a blue shift as compared to the pure bulk water, which conjecture the presence of weaker hydrogen bond network in a droplet. © 2017 Wiley Periodicals, Inc.

Aluminum oxynitride, which can be regarded a nitrogen-stabilized cubic γ-Al2O3, has attracted attention in terms of its good mechanical, chemical and optical stability. Because of its optical inertness, however, photoluminescence (PL) emission from nominally pure aluminum oxynitride has not been carefully investigated and evaluated. In this work, we prepared visibly luminescent aluminum oxynitride by nitridation of γ-Al2O3 under N2 atmosphere without adding AlN using a high-frequency induction heating unit. The resulting aluminum oxynitride exhibits a broad PL emission in the blue/green spectral region under excitation with light of ~260 nm. In the luminescent aluminum oxynitride sample, the excitation and emission events will occur at different sites; the electron transfer from the excitation site to the emission site is preceded by the radiative recombination process. It has also been found that the PL peak wavelength shows an anomalous blue shift by ~50 nm with increasing temperature from 78 to 500 K. The observed temperature dependent PL characteristics are governed by thermalization among multiple emitting levels. Aluminum vacancies and oxygen vacancies, both of which are introduced into the crystalline lattice during nitridation without the presence of AlN, are very likely candidates for the excitation and emission centers, respectively. Hence, the present direct nitridation method provides a simple and effective way to add an additional optical functionality to otherwise optically inactive aluminum oxynitride. This article is protected by copyright. All rights reserved.

Semiclassical ab initio simulations of the absorption spectra of neutral and anionic p-hydroxybenzylidene-2,3-dimethylimidazolinone (p-HBDI), a model chromophore of green fluorescent protein (GFP) and of a positively charged neutral (N+)-HBDI chromophore model, were performed in gas phase with the resolution-of-identity algebraic diagrammatic construction through second-order (RI-ADC(2)) method. The calculated absorption spectra in gas phase are composed of one band centered at 3.51 eV (HBDI), 2.50 eV (HBDI- ) and 3.02 eV ((N+)-HBDI) owing to the absorption of the first 1 ππ* transition. Band maxima are redshifted by ~0.1 eV with respect to the corresponding vertical energies. The COSMO-RI-ADC(2) calculations of the first vertical excitation energy of HBDI, HBDI- and (N+)-HBDI forms in polar solution including microsolvation simulate the observed solvent redshift for neutral HBDI and the solvent blueshift of the HBDI- and (N+)-HBDI forms. The state-specific solvation approach applied to TDDFT calculations reproduced the experimental solvent shifts for the three HBDI forms, demonstrating a more accurate theoretical description as compared to the linear-response TDDFT approach.

The microscopic and dynamic response of the atactic polystyrene molecules under shock compression at laser power density of 4.9 GW/cm2 was studied using time-resolved Raman spectroscopy. The shock pressure estimated in the polystyrene sample was 2 GPa, and the temporal and wavenumber resolutions in these experiments were 3 ns and 3 cm−1, respectively. The shocked polystyrene showed a blue shift of 5 and 7 cm−1 for the 1004 cm−1 (C―C―C ring bending mode ν12) and 1606 cm−1 (C―C ring stretching mode ν8a. , respectively. The changes in ν12 and ν8a modes are observed with respect to shock wave propagation. It is observed that the intensities of the Raman peaks decrease and the FWHM of the modes increase due to formation of additional new peaks with delay. The reason behind this indicates the mechanical processes associated with the uniaxial nature of the shock compression. The shock velocity inside the polystyrene was calculated as 2.9±0.12 km/s using the evolution of intensity ratio of peaks with time. This is in good agreement with the shock velocity (3.0 km/s) deduced from the 2D simulations, performed using three temperature radiation hydrodynamic code, THRD. Copyright © 2017 John Wiley & Sons, Ltd.

Luminescence technology has been improved with the help of semiconductor nanoparticles that possess novel optical and electrical properties compared with their bulk counterpart. The aim of this study was to design semiconductor nanocrystals in their pure (ZnS) or doped form (ZnS:Mn) with different concentrations of Mn2+ ions by a wet chemical route stabilized by ethylenediamine tetra-acetic acid (EDTA) and to evaluate their luminescence properties. The nanocrystals were characterized by physicochemical techniques such as X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SEAD), EDS, and ultraviolet (UV)-visible light and photoluminescence (PL) studies. These results showed the presence of cubic phase and spherically shaped nanocrystals. A blue shift with respect to their bulk counterpart was observed. PL emission spectra were observed with a fixed blue peak and the yellow-orange bands were red shifted towards the red region under the same excitation wavelength. The orange-red bands were attributed to the radiation transition of electrons in 3d5 unfilled shells of Mn2+ ions [4 T1 (4 G)-6 A1 (6 S)]; the ZnS matrix varied with Mn2+ concentration. Shift and increase in the intensity of the PL and absorption bands were observed with increase in Mn content. The study showed that Mn2+ -doped ZnS nanocrystal emission bands can be tuned from the yellow-orange to the red regions under a controlled synthesis process and could be used as promising luminescent emitters in the biology field upon functionalization with suitable materials. Further studies on construction with various other materials will be useful for practical applications.

Eu-doped transparent oxyfluoride aluminosilicate glass was prepared by controlling with Al codoping of melt-quenched glass fabricated under air atmosphere. In the presence of Al input, the photoluminescence emission spectra under 393 nm excitation shows a blue shift by adjusting the ratio of Eu3+ and Eu2+. After heat treatment of glass, the ratio of Eu3+ and Eu2+ of luminescence emission were changed by controlling treatment temperature. The PL intensity of Eu3+ and Eu2+ ions in the glass-ceramics (GC) was much stronger than in the precursor glass (PG). The possible mechanism responsible for color tuneability of the ratio of Eu3+ and Eu2+ doped was discussed.

Herein, silicon quantum dot light‐emitting diodes (SiQD LEDs) are investigated to explore the interplay between their electroluminescence (EL) blue shift and the SiQD ligand length on the SiQD surface. The ligand is essential for LED fabrication to ensure colloidal stability, but it also hinders efficient charge transport inside the LED. Consequently, the SiQDs are functionalized via organolithium reagents with hexyl, octyl, and dodecyl to obtain a low‐SiQD surface coverage and therefore improved charge transport. With increasing ligand length, the potential barrier between the SiQDs increases, which is ideal for charge carrier confinement, but a trade‐off with the charge transport has to be found. A sweet spot for LED performance is found for octyl‐functionalized SiQDs with the highest irradiance (734 μW cm−2) and external quantum efficiency (1.48%), compared with shorter hexyl‐ and longer dodecyl‐capped SiQDs. The SiQDs exhibit a size distribution, whereas the bandgap energy of SiQDs is inversely proportional to the SiQD size. Therefore, large SiQDs with a short ligand are accessible at low voltages, whereas small SiQDs with long ligands require elevated voltages. This leads to a broadening and a blue shift of the EL spectrum and a ligand length‐controlled size‐selective SiQD activation.

Raman spectroscopy is employed to investigate bond phonon relaxation of layered (Mo, W)‐(S 2 , Se 2 ) by using the stimuli of number‐of‐layer. The results demonstrate that the dimer interaction dictates the blue shift of the E 1 2g phonon but the collective interaction of an atom with its z ‐neighbors governs the red shift of the A 1g phonon dynamics as the number‐of‐layer reduces.

Nanophosphors of (Sr0.98-x Mgx Eu0.02 )2 SiO4 (x = 0, 0.18, 0.38, 0.58 and 0.78) were prepared through low temperature solution combustion method and their luminescence properties were studied. The emission peak for Eu2+ -doped Sr2 SiO4 nanophosphor is observed at ~490 nm and ~553 nm corresponding to two Sr2+ sites Sr(I) and Sr(II) respectively for 395 nm excitation. However the addition of Mg2+ dopant in Sr2 SiO4 leads to suppression of ~553 nm emission peak due to absence of energy levels of Sr (II) sites which results in a single broad emission at ~460 nm. It was shown that the emission peak blue shifted with increase in Mg concentration which may be attributed to change in crystal field environment around Sr(I) sites. Therefore, the (Mg0.78 Sr0.20 Eu0.02 )2 SiO4 nanophosphor can be used for blue emission and the Sr2 SiO4 :Eu0.042+ for green-yellow emission at 395 nm excitations. The Commission International de L'Eclairage (CIE) chromaticity coordinates for mixed powders of (Mg0.78 Sr0.20 Eu0.02 )2 SiO4 and Sr2 SiO4 :Eu0.042+ (in a 1:1 ratio) fall in the white region demonstrating the possible use of the mixture in white light generation using near-UV excitation source.

Samples of the Ba9 (Lu2-x Yx )Si6 O24 :Ce3+ (x = 0-2) blue-green phosphors were synthesized by solid-state reactions. All the samples exhibited a rhombohedral crystal structure. As the Y3+ concentration increased, the diffraction peaks shifted to the small angle region and the lattice parameters increased due to the larger ionic radius of Y3+ (r = 0.900 A) compared with that of Lu3+ (r = 0.861 A). Under 400 nm excitation, samples exhibited strong blue-green emissions around 490 nm. The emission bands had a slight blue shift that resulted from weak crystal-field splitting with increasing Y3+ concentration. Luminescence intensity and quantum efficiency (QE) decreased with increasing Y3+ concentration. The internal QE decreased from 74 to 50% and the external QE decreased from 50 to 34% as x increased from 0 to 2. The thermal stability of the Lu series was better than that of the Y-series. The excitation band peak around 400 nm matched well with the emission light from the efficient near-ultraviolet (NUV) chip. These results indicate promising applications for these NUV-based white light-emitting diodes.

In order to improve the luminescent performance of silicate blue phosphors, Sr(1.5-x)-(1.5y) Mg0.5 SiO4 :xEu2+ ,yCe3+ phosphors were synthesized using one-step calcination of a precursor prepared by chemical co-precipitation. The crystal structure and luminescent properties of the phosphors were analyzed using X-ray diffraction and fluorescence spectrophotometry, respectively. Because the activated ions (Eu2+ ) can occupy two different types of sites (Sr1 and Sr2 ), the emission spectrum of Eu2+ excited at 350 nm contains two single bands (EM1 and EM2 ) in the wavelength range 400-550 nm, centered at 463 nm, and the emission intensity first increases and then decreases with increasing concentrations of Eu2+ ions. Co-doping of Ce3+ ions can greatly enhance the emission intensity of Eu2+ by transferring its excitation energy to Eu2+ . Because of concentration quenching, a higher substitution concentration of Ce3+ can lead to a decrease in the intensity. Meanwhile, the quantum efficiency of the phosphor is improved after doping with Ce3+ , and a blue shift phenomenon is observed in the CIE chromaticity diagram. The results indicate that Sr(1.5-x)-(1.5y) Mg0.5 SiO4 :xEu2+ ,yCe3+ can be used as a potential new blue phosphor for white light-emitting diodes.

We have carried out Raman spectroscopic measurements on atactic polystyrene (aPS) under shock compression up to 2 GPa. Observed wavenumber shifts of Raman active modes have been used to determine their Gruneisen parameters and bond anharmonicities. Raman mode at 798 cm−1 displays maximum blue shift of 4.95 cm−1/GPa. Our observed wavenumber shifts under shock compression are found to be consistent with the earlier results obtained under hydrostatic pressure. We have also evaluated pressure through 1D radiation hydrodynamic simulations, and the results are found to be in good agreement with the experimental values. The pressure induced wavenumber shifts and line width changes of the present study can be utilized as a gauge for pressure measurement because of laser induced shock front. Copyright © 2016 John Wiley & Sons, Ltd.

This study demonstrated the feasibility of fabricating a highly stacked vertically aligned InGaAs/GaAs(Sb) quantum dot (QD) structure with an AlGaAsSb spacer layer for improving the device performance of QD intermediate-band solar cell (QD-IBSC) devices. The power-dependent photoluminescence measurements of the proposed structure revealed a blueshift in the QD ground-state emissions when the excitation power was increased, indicating the formation of an intermediate band inside the QD structure. Capping the InGaAs QDs with a GaAsSb layer prevented the QDs from collapsing because there was less In–Ga intermixing between the QDs and GaAsSb layer. In addition to maintaining the QD structure, the carrier lifetime was extended by tuning the energy band alignment of the InGaAs/GaAsSb QD structure. Inserting the AlGaAsSb layer into the spacer layer increased the band gap, which in turn increased the open-circuit voltage of the QD-IBSC. The QD-IBSC in this work shows an extension of external-quantum efficiency by up to 1200 nm (compared with a GaAs reference cell) through the absorption by QDs and increased the open-circuit voltage from 0.67 to 0.70 V by adopting the AlGaAsSb spacer layer. These results confirm that adopting a columnar InGaAs/GaAs(Sb) QD structure with a AlGaAsSb spacer layer can enhance the performance of QD-IBSC devices. Copyright © 2016 John Wiley & Sons, Ltd.

A density functional theory study is performed to predict the structures and stability of carbon monoxide (CO) bound EX3+ (E = C, Si, Ge, Sn, Pb; X = H, F, Cl, Br, I) complexes. The possibility of bonding through both C- and O-sides of CO is considered. Thermochemical analysis reveals that all the dissociation processes producing CO and EX3+ are endothermic in nature whereas most of the dissociation reactions are endergonic in nature at room temperature. The nature of bonding in EC/O bonds is analyzed via Wiberg bond index, natural population analysis, electron density, and energy decomposition analyses in conjunction with natural orbitals for chemical valence scheme. In comparison to CO stretching frequency ( ν∼CO) in free CO, while a red shift is noted in O-side binding, the C-side binding results in a blue shift in ν∼CO. The relative change in ν∼CO values in CO bound EX3+ complexes on changing either E or X is scrutinized and possible explanation is provided in terms of polarization in the σ- and π-orbitals and the relative strength of C→E or O→E σ-donation and E→C or E→O π-back-donation. © 2016 Wiley Periodicals, Inc.

The overmuch rare lead arsenic sulfosalts, baumhauerite (Pb3As4S9), dufrenoysite (Pb2As2S5), gratonite (Pb9As4S15), sartorite (PbAs2S4), and seligmannite (PbCuAsS3), were investigated by Raman spectroscopy. Raman spectra of the investigated minerals arise from the stretching and bending modes of the isolated and interconnected AsS3 pyramidal groups. The As–S stretching vibrations of the studied minerals occur between 390 and 340 cm−1, whereas those of S–As–S bending modes between 335 and 220 cm−1. The shorter bond distances of the As–S readily elucidate the blue shift from seligmannite to gratonite, sartorite, dufrenoysite, and baumhauerite and the increase in full width at half maximum in similar modes. Copyright © 2016 John Wiley & Sons, Ltd.

Longer carrier diffusion length and improved power conversion efficiency have been reported for thin-film solar cell of organolead mixed-halide perovskite MAPbI3- x Cl x in comparison with MAPbI3 . Instead of substituting I in the MAPbI3 lattice, Cl-incorporation has been shown to mainly improve the film morphology of perovskite absorber. Well-defined crystal structure, adjustable composition (x), and regular morphology, remains a formidable task. Herein, a facile solution-assembly method is reported for synthesizing single-crystalline nanofibers (NFs) of tetragonal-lattice MAPbI3- x Cl x with the Cl-content adjustable between 0 ≤ x ≤ 0.75, leading to a gradual blueshift of the absorption and photoluminescence maxima from x = 0 to 0.75. The photoresponsivity (R) of MAPbI3 NFs keeps almost unchanging at a value independent of the white-light illumination intensity (P). In contrast, R of MAPbI3- x Cl x NFs decreases rapidly with increasing both the x and P values, indicating Cl-substitution increases the recombination traps of photogenerated free electrons and holes. This study provides a model system to examine the role of extrinsic Cl ions in both perovskite crystallography and optoelectronic properties.

Colloidal assemblies develop pronounced structural colors due to the selective diffraction of light. Micropatterns with multiple structural colors are appealing for the use in a variety of photonic applications. Here, a lithographic approach is reported, which provides a high level of control over the size, shape, and color of a micropattern using the anisotropic shrinkage of inverse opals made of a negative photoresist heated to high temperatures. Shrinkage occurs uniformly across the thickness of the film, leading to a blueshift in the structural color while maintaining a high reflectivity across the full visible spectrum. The rate of shrinkage is determined by the annealing temperature and the photoresist crosslinking density. The rate can, therefore, be spatially modulated by applying UV radiation through a photomask to create multicolor micropatterns from single-colored inverse opals. The lateral dimensions of the micropattern features can be as small as the thickness of the inverse opal.

We report on the formation of Tamm plasmon (TP) modes in the visible spectral region at the interface between a Ag film and a ZnSe-based distributed Bragg reflector (DBR). The tuning of the TP eigenenergies within the stop-band in dependence on the DBR top layer thickness is investigated by micro-reflectivity measurements. The experimental findings are compared with calculations using the transfer matrix method. The latter calculations show that strong coupling can be achieved between quantum well (QW) excitons and the TP modes. In addition, the Rabi-splitting energy can be enhanced in a simple TP structure by increasing the number of QWs inside the top layer of the DBR. When a metal layer is deposited on a cold MC sample, micro-reflectivity spectra show a blue shift of the cavity resonance. The TP modes are likewise observed in the same MC sample when reducing the top layer thickness of the DBR. This shift of cavity resonance and formation of TP mode are in good agreement with calculations. These results are rather promising in order to realize a spatial confinement of the polaritons by utilizing metal strips. Such channeling of polaritons opens the way to practical demonstration of exciton-polariton integrated circuits. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The structural and optical properties of commercially obtained Y3 Al5 O12 :Ce3+ phosphor were investigated by replacing Al3+ with Ga3+ and Y3+ with Gd3+ in the Y3 Al5 O12 :Ce3+ structure to form Y3 (Al,Ga)5 O12 :Ce3+ and (Y,Gd)3 Al5 O12 :Ce3+ . X-Ray diffraction (XRD) results showed slight 2-theta peak shifts to lower angles when Ga3+ was used and to higher angles when Gd3+ was used, with respect to peaks from Y3 Al5 O12 :Ce3+ and JCPDS card no. 73-1370. This could be attributed to induced crystal-field effects due to the different ionic sizes of Ga3+ and Gd3+ compared with Al3+ and Y3+ . The photoluminescence (PL) spectra showed broad excitation from 350 to 550 nm with a maximum at 472 nm, and broad emission bands from 500 to 650 nm, centred at 578 nm for Y3 Al5 O12 :Ce3+ arising from the 5d → 4f transition of Ce3+ . PL revealed a blue shift for Ga3+ substitution and a red shift for Gd3+ substitution. UV-Vis showed two absorption peaks at 357 and 457 nm for Y3 Al5 O12 :Ce3+ , with peaks shifting to 432 nm for Ga3+ and 460 nm for Gd3+ substitutions. Changes in the trap levels or in the depth and number of traps due to Ce3+ were analysed using thermoluminescence (TL) spectroscopy. This revealed the existence of shallow and deep traps. It was observed that Ga3+ substitution contributes to the shallowest traps at 74 °C and fewer deep traps at 163 °C, followed by Gd3+ with shallow traps at 87 °C and deep traps at 146 °C. Copyright © 2016 John Wiley & Sons, Ltd.

This study reports the synthesis and photophysical properties of a star-shaped, novel, fluoranthene-tetraphenylethene (TFPE) conjugated luminogen, which exhibits aggregation-induced blue-shifted emission (AIBSE). The bulky fluoranthene units at the periphery prevent intramolecular rotation (IMR) of phenyl rings and induces a blueshift with enhanced emission. The AIBSE phenomenon was investigated by solvatochromic and temperature-dependent emission studies. Nanoaggregates of TFPE, formed by varying the water/THF ratio, were investigated by SEM and TEM and correlated with optical properties. The TFPE conjugate was found to be a promising fluorescent probe towards the detection of nitroaromatic compounds (NACs), especially for 2,4,6-trinitrophenol (PA) with high sensitivity and a high Stern-Volmer quenching constant. The study reveals that nanoaggregates of TFPE formed at 30 and 70% water in THF showed unprecedented sensitivity with detection limits of 0.8 and 0.5 ppb, respectively. The nanoaggregates formed at water fractions of 30 and 70% exhibit high Stern-Volmer constants (Ksv=79,998 and 51,120 M(-1), respectively) towards PA. Fluorescence quenching is ascribed to photoinduced electron transfer between TFPE and NACs with a static quenching mechanism. Test strips coated with TFPE luminogen demonstrate fast and ultra-low-level detection of PA for real-time field analysis.

Hybrid materials with hierarchical nanostructures are of great interest for their advanced functions. However, the effect of the formation of hierarchical nanostructures on properties is not well understood. Here, through combining dissipative particle dynamics simulation and the finite-difference time-domain method, the optical properties of hierarchically ordered nanostructures formed by mixtures of A(BC)n multiblock copolymers and nanoparticles (NPs) are investigated. A series of hierarchically ordered nanostructures with multiple small-length-scale hybrid domains are obtained from the self-assembly of A(BC)n /NP. An increase and blueshift in optical absorption are observed when the number of small-length-scale hybrid domains increases. The small-length-scale hybrid domains enhance light scattering, which consequently contributes to the improved optical performance. These findings can yield guidelines for designing hierarchically ordered functional nanocomposites with light-harvesting characteristics.

Radio frequency sputtering is a low-cost technique for the deposition of large-area single-phase AlInN on silicon layers with application in photovoltaic devices. Here we study the effect of the Al mole fraction x from 0 to 0.56 on the structural, morphological, electrical and optical properties of n-AlxIn1-xN layers deposited at 550oC on p-Si(100) by radio frequency sputtering. X-ray diffraction data show a wurtzite structure oriented along the c-axis in all samples, where the full width at half maximum of the rocking curve around the InN (0002) diffraction peak decreases from ~9o to ~3o when incorporating Al to the AlInN layer. The root mean square surface roughness, estimated from atomic force microscopy, evolves from 20 nm for InN to 1.5 nm for Al0.56In0.44N. Low-temperature photoluminescence spectra show a blue shift of the emission energy from 1.59 eV (779 nm) for InN to 1.82 eV (681 nm) for Al0.35In0.65N accordingly to the Al content rise. Hall effect measurements of AlxIn1-xN (0 < x < 0.35) on sapphire samples grown simultaneously point a residual n-type carrier concentration in the 1021 cm-3 range. The developed n-AlInN/p-Si junctions present optimal material properties to explore their performance operating as solar cell devices.

Physical vapor deposition (PVD) is used to grow CdTe thin films of different thicknesses on glass substrates. The characterization of the samples is then investigated optically and structurally. Three experimental techniques were used in this study; optical absorption (ABS), Raman, and X-ray diffraction (XRD) spectroscopies. In optical ABS spectroscopy, the Urbach energy related to the width of long-wavelength tail decreases from 827 to 585 meV as the thickness increases from 100 to 500 nm, respectively. The thickness-dependent particle size was calculated using the value of the size-dependent optical absorption edge energy. A shift of 710 meV in the ABS edge energy takes place as the thickness increases from 100 to 500 nm. Thickness-dependent shifting and widening of XRD line is presumably due to the size effect and strain. Relative to the phonon frequency of bulk CdTe crystal, a thickness-dependent blueshift was observed in Raman spectra for the Longitudinal Optical (LO) phonon frequency, while a redshift for the longitudinal acoustic (LA) and transverse optical (TO) phonon frequencies is observed. In the present work, the results of optical absorption, XRD, and Raman analyses are combined in order to study the effect of particle-size evolution, thickness-dependent strain, and structural disorder.

The growth and optical properties of InAs quantum dots on a pure zinc blende InP nanowire are investigated. The quantum dots are formed in Stranski–Krastanov mode and exhibit pure zinc blende crystal structure. A substantial blueshift of the dots peak with a cube-root dependence on the excitation power is observed, suggesting a type-II band alignment. The peak position of dots initially red-shifts and then blue-shifts with increasing temperature, which is attributed to the carrier redistribution among the quantum dots. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

We have investigated the exciton-polariton condensation in a CuBr microcavity with HfO2/SiO2 distributed Bragg reflectors, focusing on condensation effects on polariton dispersion relations. The polariton distribution as a function of in-plane wave vector k// under illumination was measured with angle-resolved photoluminescence (PL) spectroscopy. In addition, we characterized the intrinsic polariton dispersion relations as reference data from analysis of the results obtained using angle-resolved reflectance spectroscopy. It was found that the polariton condensation causes a large blueshift of the lower polariton branch (LPB) and a flat dispersion relation around the ground state at k//=0. The renormalized dispersion relation of the LPB under the polariton condensation was quantitatively analysed using a theory for a diffusive Goldstone mode peculiar to nonequilibrium condensation. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An unexpected spectrum blue shift of the yellow emission was observed for solid solution phosphors Ba2−xSrxMg(PO4)2:Eu2+ (x = 0–1.5), when bigger ions Ba2+ were substituted by smaller ions Sr2+ in Ba2Mg(PO4)2 lattices. The solid solution phosphors were prepared by a solid-state reaction to clarify the local sites environment of activators Eu2+ and tune the anomalous long-wavelength yellow emission. BaSrMg(PO4)2 phase was identified to be isostructural with Ba2Mg(PO4)2 by Rietveld refinements. DFT calculation and photoluminescence show that the activator ions Eu2+ in BaSrMg(PO4)2 occupy Sr2+ and Ba2+ sites at an equal probability and both generate an anomalous yellow emission. The yellow emission from Ba2−xSrxMg(PO4)2:Eu2+ was gradually blue shift with increasing Sr2+ substitution concentration x from 0.1 to 1. Such unusual blue shift is interpreted based on the evolution of crystal structure parameters due to Sr2+ substitution, and subsequently, a site environmental expansion mechanism is proposed. The proposed mechanism could serve as a general model to reveal the underlying factors for spectrum shift caused by cation substitution and contribute to design new solid solution phosphors.

Transparent and colorless CeO2-activated borogermanate glasses, with the nominal molar composition of 25B2O3–40GeO2–14Gd2O3–1CeO2–(20−x) BaO–xBaF2 (x = 0, 2.5, 5, 10, 15 and 20), were synthesized by a melt-quenching method in air. Their optical investigation on the transmittance, photoluminescence (excitation and emission spectra), the luminescence decay curves, as well as the temperature-dependent Ce3+ emission are studied systematically with the gradual substitution of BaF2 for BaO. The room-temperature photoluminescence results reveal that the emission intensity can be improved by about 2.5 times with the full substitution of BaF2 for BaO. The blue shift of the cut-off edge, excitation and emission spectra of Ce3+-activated borogermanate glass, and the emission intensity of Ce3+ ions as a function of temperature range in 80–500 K are also discussed.

A series of blue phosphors Ca(1.98-x)M(x)PO4Cl:0.02Eu(2+) (M = Mg and Sr) with different values of x were synthesized using a high-temperature solid-state reaction. X-Ray diffraction and photoluminescence measurements were used to study the phase structure and luminescence properties. Ca2PO4Cl:0.02Eu(2+) exhibits a tunable emission intensity and color due to the incorporation of Sr(2+) or Mg(2+). The incorporation of Sr(2+) reduces the luminescence intensity and results in a slight red shift in the emission band. The incorporation of Mg(2+) results in enhanced emission and a clear blue shift in the emission band along with a tunable chromatic coordination. Under excitation at λ = 334 nm, the emission intensity of the Mg(2+)-doped Ca2PO4Cl:0.02Eu(2+) is found to be 250% that of Ca2PO4Cl:0.02Eu(2+). The luminescence behaviors of the as-synthesized phosphors are discussed according to the host crystal structure and site occupancy of Eu(2+). The results indicate that Mg(2+)-doped Ca2PO4Cl:Eu(2+) is more applicable as a near-UV-convertible blue phosphor for white light-emitting diodes.

Films of poly(vinyl alcohol)/cadmium sulphide (PVA/CdS) nanocomposite containing various concentrations of Cd2+ ions were prepared using gamma radiation at different doses from 50 up to 200 kGy. The UV/VIS spectra revealed that the CdS/PVA nanocomposites showed blue shift for the absorption peak as compared with bulk CdS. As the irradiation dose increased, a gradual red shift in the wavelength accompanying with broadening of the absorption peak was observed. The estimated optical band gap energies and the calculated CdS particle sizes of (PVA/CdS) showed correlation between their values and the variable parameters (irradiation dose and Cd+2:S−2 molar ratio). Transmission electron microscopy images showed that the CdS/PVA nanocomposites were dispersed as spherical CdS nanoparticles with homogeneity at either lower concentration of CdCl2 or irradiation dose. The nano-rod structures of CdS was accompanied with small agglomeration at either higher CdCl2 concentration or irradiation dose. A cubic phase and mixture of cubic and hexagonal phases of the prepared CdS nanoparticles were formed at lower and higher CdCl2 concentrations, respectively. Fourier Transform Infrared spectra confirmed the coordination of CdS nanoparticles with the hydroxyl groups of PVA matrix. POLYM. ENG. SCI., 55:2583–2590, 2015. © 2015 Society of Plastics Engineers

With increasing miniaturization, it is extremely important to maintain the magnetization stability at small scale. Herein, more efforts and interests focus on the interface of magnetic core and semiconductor shell to obtain desired magnetic and/or luminescent properties. Here, Fe3O4 nanocubes are synthesized via a thermal decomposition followed by coating ZnO nanocrystals. To create a large interface, large Fe3O4 nanocubes with 78 ± 3 nm average side-length are synthesized through adjusting the ratio of iron precursor to stabilizer. The average diameter of the particular ZnO nanostructures coated on the nanocubic Fe3O4 is around 10 ± 2 nm. In addition to the photoluminescent properties of the ZnO-coated nanostructures, core-shell Fe3O4@ZnO nanostructures demonstrate enhanced UV absorption at 360 nm, which has a 20 nm blueshift compared to bulk ZnO. The superparamagnetic properties of Fe3O4@ZnO core–shell hybrid nanocrystals at room temperature are dominated by the ferromagnetic properties when the temperature is lower than the Blocking temperature, 235.7 K. The observed exchange bias and temperature-dependent magnetization can result from the interfacial interphase between ZnO and Fe3O4. The anisotropy contributed by the interfacial interphase allows the nanostructures to maintain stable magnetization in miniaturized devices.

Li0.995−xMgxSi2−xAlxN3: Eu2+0.005 (LSN: xM) (0 ≤ x ≤ 0.04) phosphors were successfully synthesized by gas-pressed sintering. Double substitution which is partial replacement of (LiSi)5+ with (MgAl)5+ is presented as a useful way to improve luminescence properties. With an increase in the substitution concentration, the intensity of the emission band of LSN: xM was enhanced and the peak position shows blue shift due to the decreased stokes shift. Furthermore, LSN: xM (0 ≤ x ≤ 0.04) shows narrower full width at half maximum and higher thermal stability than Li0.995Si2N3: Eu2+0.005.

Trace quantities of hydrogen-bonding impurities in otherwise highly purified and dried glassy hydrocarbon matrices at 77 K can modify the relative triplet state energy levels, and hence the photophysical properties of two aromatic ketones, xanthone and chromone, to the extent that the intrinsic spectroscopic properties are obscured. The intrinsic spectroscopic properties of each are revealed in multicrystalline n-alkane Shpol'skii matrices, and also can be observed in rigorously purified and dried hydrocarbon glasses at 77 K. The extreme sensitivity to stoichiometric, and even substoichiometric quantities of hydrogen-bonding impurities arises from the near-degeneracy of the two lowest-lying triplet states, and the sensitive nature of the n→π* blueshift phenomena to specific hydrogen-bonding interactions.

The evolution of Curie–Weiss temperature (Θ) has been investigated in thiol-capped Fe-doped wurtzite (WZ) and zincblende (ZB) CdS nanoparticles. Fe doped CdS nanoparticles with different crystal structures namely WZ and ZB have been obtained by varying its synthesis temperature. It has been found that the magnetic impurity ions are distributed randomly in ZB samples, whereas it form clusters near the surface of WZ CdS nanoparticles. These distributions of magnetic impurities ions alter the density of charge carriers and hence have a significant effect on Θ. An increase in Θ by nearly an order of magnitude has been observed in WZ, as compared to the ZB CdS nanoparticles, which is explained well by considering a relative variation in inter-Fe separation in the two polymorphs of CdS within the framework of the Heisenberg model. Spatial distribution of Fe3+ ions in ZB and WZ CdS nanoparticles. A blueshift in the UV–visible absorption spectra is observed due to etching, which removes more Fe3+ ions in WZ CdS.

Three new hybrid iodoargentates (H2pipe)0.5(α-AgI2) (1), (Me2teda)0.5(α-AgI2) (2), and (H2dpe)0.5(β-AgI2) (3) have been synthesized under solvothermal conditions, whereby the aliphatic organic cations (H2pipe)2+ and (Me2teda)2+ (pipe = piperazine, teda = triethylenediamine) and the conjugated organic cation (H2dpe)2+ [dpe = 1,2-di(4-pyridyl)ethylene] exhibit different contributions to both the crystal and electronic structures. The (H2pipe)2+ and (Me2teda)2+ cations direct the formation of α-type (AgI2)– polyanionic chains and influence the bandgaps of 1 and 2 indirectly by modulating the iodoargentate anionic structures. By contrast, the (H2dpe)2+ cation directs the formation of a novel β-type (AgI2)– chain and changes the bandgap of 3 directly to make up the bottom of the conduction band. From 1 and 2 to 3, a direct to indirect bandgap transformation and reduced bandgap can be observed (3.74, 2.88, and 1.99 eV for 1–3, respectively). Relative to the bandgap of bulk AgI2, the bandgaps of 1 and 2 show a blueshift as a result of the quantum confinement effect, whereas the bandgap of 3 shows a redshift owing to the direct participation of the conjugated cation (H2dpe)2+ in adjusting the bandgap.