Single-component materials with both fluorescence and room-temperature phosphorescence (RTP) are useful for ratiometric sensing and imaging applications. On the basis of a general design principle, an amino-substituted benzophenone is covalently incorporated into waterborne polyurethanes (WPU) and results in fluorescence and RTP single-component dual-emissive materials (SDMs). At different aminobenzophenone concentrations, the statistical, thermal, and optical properties of these SDMs are characterized. Despite their similar thermal behaviors, the luminescence properties as a function of the chromophore concentration are quite different: increasing concentrations led to progressively narrowed singlet-triplet energy gaps. The tunability of fluorescence and RTP via chromophore concentration is explained by a previously proposed model, polymerization-enhanced intersystem crossing (PEX). The proposal of PEX is based on Kasha's molecular exciton theory with a specific application in polymeric systems, where the polymerization of luminophores results in excitonic coupling and enhanced forward and reverse intersystem crossing. The mechanism of PEX is also examined by theoretical calculations for the WPU system. It is found that the presence of K1 aggregates indeed enhances the crossover from singlet excited states to triplet ones.

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Direct bandgap III-V semiconductor lasers grown on silicon (Si) are highly desired for monolithic integration with Si photonics. Fabrication of semiconductor lasers with a Fabry–Pérot cavity usually includes facet cleavage, however, that is not compatible with on-chip photonic integration. Etching as an alternative approach holds a great advantage in preparing cavity mirrors with no need of breaking wafer into bars. However, gallium nitride (GaN) sidewalls prepared by dry etching often have a large roughness and etching damages, which would cause mirror loss due to optical scattering and carrier injection loss because of surface non-radiative recombination. A wet chemical polishing process of GaN sidewall facets formed by dry etching was studied in detail to remove the etching damages and smooth the vertical sidewalls. The wet chemical polishing technique combined with dry etching was successfully applied to the on-wafer fabrication of cavity mirrors, which enabled the realization of room temperature electrically injected InGaN-based laser diodes grown on Si.

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This letter reports a successful fabrication of room-temperature electrically injected AlGaN-based near-ultraviolet laser diode grown on Si. An Al-composition step down-graded AlN/AlGaN multilayer buffer was carefully engineered to not only tackle the huge difference in the coefficient of thermal expansion between AlGaN template and Si substrate, but also reduce the threading dislocation density caused by the large lattice mismatch. On top of the crack-free n-AlGaN template, high quality InGaN/AlGaN quantum wells were grown, sandwiched by waveguide and optical cladding layers, for the fabrication of edge-emitting laser diode. A dramatic narrowing of the electroluminescence spectral line-width, an elongated far-field pattern, and a clear discontinuity in the slope of light output power plotted as a function of the injection current provide an unambiguous evidence of lasing.

A robust model for estimating crop residue cover by remote sensing is required to better quantify management of crop residue in agricultural fields. There is a notable lack of robustness in the model, however, when the moisture contents of soil and crop residue vary. To minimize the influence of soil and crop residue moisture on spectral reflectance, we applied a preprocessing method, external parameter orthogonalization (EPO), which estimates the influence of moisture variation on reflectance by performing a principal component analysis on a small set of spectra that represent the variation in moisture. In this study, reflectance spectra (400–2400 nm) for four soils and four crop residues with different moisture conditions were acquired in the laboratory. Reflectance values of mixed scenes with varying proportions of crop residue and soil were simulated using a linear mixture model. The results indicated that moisture significantly affected the cellulose absorption index, the lignin–cellulose absorption index, and the relationships between crop residue cover and these two indices. For applying EPO to remove moisture effects, we proposed two strategies of EPO application that corresponded to two scenarios: a change in moisture in either soil or crop residue, and a change in moisture in both soil and crop residue. The results demonstrated that EPO was able to effectively remove the moisture effects and that the calibration model was more robust after EPO. This study helps to quantify and remove the effects of moisture on the estimation of crop residue cover.

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