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Soil thermal conductivity (λ) is an important parameter to describe the heat transfer ability of soil, which is of great significance to engineering construction in permafrost and seasonally frozen regions. Its values are highly dependent on soil type, composition, and texture. Therefore, the thermal conductivity of special soils needs to be studied distinctively. Turfy soil is a widely distributed special kind of humus soil, with characteristics of high-porosity ratio, high-water content, high-permeability, and high-organic matter. Here, fundamental properties of turfy soil from Changbai Mountains, northeastern China, were determined, and thermal conductivity was investigated using the steady-state comparison method. The results revealed that the thermal conductivity of unfrozen and frozen turfy soil was about 0.58 W∙m−1 k−1 and 1.32 W∙m−1 k−1, respectively, and phase transition in soil mainly happened from –2 to –3 ℃. Thermal conductivity of unfrozen turfy soil was negative correlated with soil water content, organic matter content, and porosity. Compared with common thermal conductivity schemes, it was found that Nikoosokhan scheme got the best prediction effect for unfrozen turfy soil, and Tian scheme was suitable for frozen turfy soil. [ABSTRACT FROM AUTHOR]

Synthesis of fluorescent carbon quantum dots (CQDs) as single light converter and their application in white light-emitting diodes (LEDs) are reported. CQDs were prepared by a one-step hydrothermal method using glucose and polyethylene glycol 200 as precursors. The structural and optical properties of the CQDs were investigated. The CQDs with uniform size of 4 nm possessed typical excitation-dependent emission wavelength and quantum yield of 3.5%. Under ultraviolet illumination, the CQDs in deionized water emitted bright blue fluorescence and produced broad visible-light emission with high red, green, and blue spectral component ratio of 63.5% (red-to-blue intensity to total intensity), suggesting great potential as single light converter for white LEDs. To demonstrate their potential, a white LED using CQDs as a single light converter was built. The device exhibited cool white light with corresponding color temperature of 5584 K and color coordinates of (0.32, 0.37), belonging to the white gamut. This research suggests that CQDs could be a promising candidate single light converter for white LEDs. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQD) emitting green photoluminescence (PL; emission peak at 500 nm) with satisfactory quantum yield (12.1%) were synthesized by a low-temperature hydrothermal method (90°C for 2 h) with l-ascorbic acid as carbon source and ethanediamine as catalyst. The as-prepared CQD dispersed readily in aqueous media, were of average diameter 6.2 nm, and their PL performance was excitation-independent. The photoluminescence wavelength of the CQD was pH-independent but the photoluminescence intensity was pH-dependent. Films of the composite materials poly(3-hexylthiophene) (P3HT) and the CQD were prepared by spin-coating and characterized by ultraviolet-visible absorption spectrophotometry and fluorescence spectrometry. The results revealed enhanced ultraviolet-visible absorption of the P3HT-CQD film compared with pure P3HT and substantially reduced PL intensity of the blend film. Experimental and theoretical results indicate the feasibility of using the CQD as a new acceptor material in polymeric photovoltaic devices. [ABSTRACT FROM AUTHOR]