The orthosilicate phosphors Sr x Ba2–x SiO4:Eu2+ have now been known for over four decades and have found extensive recent use in solid-state white lighting. It is well-recognized in the literature and in practice that intermediate compositions in the solid-solutions between the orthosilicates Sr2SiO4 and Ba2SiO4 yield the best phosphor hosts when the thermal stability of luminescence is considered. We employ a combination of synchrotron X-ray diffraction, total scattering measurements, density functional theory calculations, and low-temperature heat capacity measurements, in conjunction with detailed temperature- and time-resolved studies of luminescence properties to understand the origins of the improved luminescence properties. We observe that in the intermediate compositions, the two cation sites in the crystal structure are optimally bonded as determined from bond valence sum calculations. Optimal bonding results in a more rigid lattice, as established by the intermediate compositions possessing the highest Debye temperature, which are determined experimentally from low-temperature heat capacity measurements. Greater rigidity in turn results in the highest luminescence efficiency for intermediate compositions at elevated temperatures.

In this study, the optical properties of nanocrystalline europium doped yttria, Y2O3:Eu3+ were investigated in dependence on different caging hosts such as porous MCM-41, porous silica, and porous alumina with pore sizes ranging between 2.7 to 80 nm. These results were compared to nanopowders measured in air and aqueous solution whose particle sizes were 5 nm and 8 nm, respectively. All these results were compared to a commercial lamp phosphor powder with a grain size of about 5 μm. The structural properties of the samples were determined by x-ray diffraction and transmission electron microscopy. Investigated optical properties are the photoluminescence emission spectra, the excitation spectra, the lifetimes, and the quantum efficiencies. A heavy dependence of the charge transfer process on the surrounding will be reported and discussed.

The production of high-quality low-defect single-domain flexible polymer opals which possess fundamental photonic bandgaps tuneable across the visible and near-infrared regions is demonstrated in an industrially-scalable process. Incorporating sub-50nm nanoparticles into the interstices of the fcc lattice dramatically changes the perceived color without affecting the lattice quality. Contrary to iridescence based on Bragg diffraction, color generation arises through spectrally-resonant scattering inside the 3D photonic crystal. Viewing angles widen beyond 40 masculine removing the strong dependence of the perceived color on the position of light sources, greatly enhancing the color appearance. This opens up a range of decorative, sensing, security and photonic applications, and suggests an origin for structural colors in Nature.

Abstract. TROPOMI (the TROPOspheric Monitoring Instrument), on board the Sentinel-5 Precursor (S5P) satellite, has been monitoring the Earth's atmosphere since October 2017 with an unprecedented horizontal resolution (initially 7 km2×3.5 km2, upgraded to 5.5 km2×3.5 km2 in August 2019). Monitoring air quality is one of the main objectives of TROPOMI; it obtains measurements of important pollutants such as nitrogen dioxide, carbon monoxide, and formaldehyde (HCHO). In this paper we assess the quality of the latest HCHO TROPOMI products versions 1.1.(5-7), using ground-based solar-absorption FTIR (Fourier-transform infrared) measurements of HCHO from 25 stations around the world, including high-, mid-, and low-latitude sites. Most of these stations are part of the Network for the Detection of Atmospheric Composition Change (NDACC), and they provide a wide range of observation conditions, from very clean remote sites to those with high HCHO levels from anthropogenic or biogenic emissions. The ground-based HCHO retrieval settings have been optimized and harmonized at all the stations, ensuring a consistent validation among the sites. In this validation work, we first assess the accuracy of TROPOMI HCHO tropospheric columns using the median of the relative differences between TROPOMI and FTIR ground-based data (BIAS). The pre-launch accuracy requirements of TROPOMI HCHO are 40 %–80 %. We observe that these requirements are well reached, with the BIAS found below 80 % at all the sites and below 40 % at 20 of the 25 sites. The provided TROPOMI systematic uncertainties are well in agreement with the observed biases at most of the stations except for the highest-HCHO-level site, where it is found to be underestimated. We find that while the BIAS has no latitudinal dependence, it is dependent on the HCHO concentration levels: an overestimation (+26±5 %) of TROPOMI is observed for very low HCHO levels (<2.5×1015 molec. cm−2), while an underestimation (-30.8%±1.4 %) is found for high HCHO levels (>8.0×1015 molec. cm−2). This demonstrates the great value of such a harmonized network covering a wide range of concentration levels, the sites with high HCHO concentrations being crucial for the determination of the satellite bias in the regions of emissions and the clean sites allowing a small TROPOMI offset to be determined. The wide range of sampled HCHO levels within the network allows the robust determination of the significant constant and proportional TROPOMI HCHO biases (TROPOMI =+1.10±0.05 ×1015+0.64±0.03 × FTIR; in molecules per square centimetre). Second, the precision of TROPOMI HCHO data is estimated by the median absolute deviation (MAD) of the relative differences between TROPOMI and FTIR ground-based data. The clean sites are especially useful for minimizing a possible additional collocation error. The precision requirement of 1.2×1016 molec. cm−2 for a single pixel is reached at most of the clean sites, where it is found that the TROPOMI precision can even be 2 times better (0.5–0.8×1015 molec. cm−2 for a single pixel). However, we find that the provided TROPOMI random uncertainties may be underestimated by a factor of 1.6 (for clean sites) to 2.3 (for high HCHO levels). The correlation is very good between TROPOMI and FTIR data (R=0.88 for 3 h mean coincidences; R=0.91 for monthly means coincidences). Using about 17 months of data (from May 2018 to September 2019), we show that the TROPOMI seasonal variability is in very good agreement at all of the FTIR sites. The FTIR network demonstrates the very good quality of the TROPOMI HCHO products, which is well within the pre-launch requirements for both accuracy and precision. This paper makes suggestions for the refinement of the TROPOMI random uncertainty budget and TROPOMI quality assurance values for a better filtering of the remaining outliers.

Control over spatial positioning of CdSe quantum dots(QDs) is a very important criterion for device fabrication. These authors utilize the ordered array of pores provided by the mesoporous material MCM‐41 to achieve this. TEM of a single CdSe@MCM‐41 particle (see Figure) shows that the hexagonally ordered mesostructure of MCM‐41 is still intact after the growth of CdSe nanoparticles inside the mesopores.

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Synthesis of 3D opaline photonic crystals has developed into a standard procedure during the last decade. [1][2][3][4][5] However, the conventional methods suffer from multiple drawbacks, with cracking and polycrystallinity [6][7][8][9] leading to degradation of the optical properties of these photonic crystals through, e.g., scattering. These special difficulties in 3D photonic crystal fabrication have hindered the utilization of the technology in commercial applications, and such photonic information technology [10] is still in its infancy. Clearly there is a need for industrial-scale, high-yield methods for producing functional photonic crystals. A novel cost-effective large-scale technique to produce flexible opals through shear-ordering during compression, utilizing a core/shell approach based on polymers, has recently been developed [11,12] and further demonstrated to have possible applications, e.g., sensor, security, and structural color applications. [13] In this Communication we present a key analysis of the 3D rheologically derived properties of shear-ordered opaline thinfilm photonic crystals using optical tracking of the strain-induced anisotropy. Probing UV-surface diffraction combined with band-gap measurements reveals a complete picture of the unit cell changes under strain. The results demonstrate that our polymer opals consist of a coherently ordered ''super-domain'' characterized by a radial director vector and show anisotropic photonic behavior depending on the relative vectorial orientation of strain and director.Shear-ordering of colloidal suspensions has been studied extensively in recent years. [14][15][16][17] In these systems the crystal ordering is dependent on both the applied shear profile and the strength of shear, and with suitable conditions long-range ordering is achieved, possibly with some dislocations or stacking faults. Our approach relies on the compression-induced shear-flow ordering of core/shell polymer particles resulting in highly-ordered solid photonic crystals with spectacular structural color features (Fig. 1a). We start with precursor core/shell particles composed of a polystyrene-polymethylmethacrylate (PS-PMMA) core and polyethylacrylate (PEA) shell. The detailed precursor preparation is described elsewhere.[11] By uniaxially compressing the precursor powder between two heated plates (Fig. 1b), we create a viscous shear flow in the polymer melt forcing the spheres to assemble into an fcclattice. The resulting structure formed here is a circular thin (ca. 300 mm) film disk (diameter 15 cm) of low-refractiveindex-contrast fcc-crystal, with the PS-PMMA cores forming the lattice and the PEA filling the interstitial sites. In this photonic crystal film the (111) planes are oriented parallel to the compression plates. [11][12][13] The (111)-plane resonance wavelength can be tuned by varying the precursor PS-PMMA particle size, and the sample can be doped with nanoparticles leading to interesting photonic behavior. [18] In this paper we show results obtained from opals us...

A series of polycrystalline Li 3 Ba 2 La 3Àx Eu x (MoO 4 ) 8 samples were prepared by the conventional solidstate reaction. The phase formation of the samples was investigated by X-ray diffraction measurements. The luminescence spectra and decay curves were studied as a function of Eu 3+ concentration and temperature. It turned out that the optical band gap of the undoped molybdates is at 3.65 eV. The quantum efficiency (QE) of the Eu 3+ doped luminescent materials increases with increasing Eu 3+ concentration and almost 100% QE was obtained for those samples doped with 70, 80, or 90% Eu 3+ . A sample containing 100% Eu 3+ showed solely a slight decrease in quantum efficiency. The luminous efficacy (LE) was 330 and 312 lm W opt À1 for the 10 and 100% Eu 3+ doped samples, respectively. The decrease of LE values is caused by a slight shift of the colour point to the red spectral range with increasing Eu 3+ content. Temperature dependent measurements revealed that Li 3 Ba 2 Eu 3 (MoO 4 ) 8 loses only 15% of efficiency up to 400 K, which demonstrates that the investigated phosphors are attractive for application in pcLEDs.