Solar steam generation provides a renewable and environmentally friendly approach to solve the water shortage issue. The pursuit of efficient, stable, and cheap photothermal agents is thus of great significance. In this work, Cu nanoparticles (NPs) fabricated simply by a substitution reaction, exhibit a near-unity (∼97.7%) light absorption, covering a broad incident angle and wavelength range (200-1300 nm). Thereby, a high photothermal conversion efficiency of 93% is achieved. The excellent photothermal performance offers a unique opportunity for the development of solar steam generation. By coating the Cu NPs on a cellulose membrane, a solar steam generation efficiency up to 73% is acquired at a low irradiation power density of 2 kW m-2 (1 kW m-2 = 1 sun). Moreover, the Cu NPs are recyclable with the high stability being resistant to heat, photoirradiation and corrosion of brine.

Large normal-direction excitation and emission of dual-emitting quantum dots (QDs) are essential for practical application of QD sensors based on the ratiometric fluorescence response. We have numerically demonstrated an all-dielectric four-layer cascaded photonic crystal (CPC) structure (alternating TiO₂ and SiO₂/SU8 layers with two dimensional nanoscale patterns in each layer) which is capable of providing normal-direction high Q-factor leaky modes at excitation wavelengths of QDs and two low Q-factor leaky modes coinciding with the two emission peaks of a dual-emitting QD. Normal-direction excitation and far-field emission of the dual-emitting QDs are enhanced significantly when QDs are distributed on/in the top TiO₂ layer of the CPC structure, especially in the spatial distribution areas of the resonant leaky modes. QDs can be positioned differently depending on the applications. Positioning QDs on the top TiO₂ layer will improve the signal-to-noise ratios of QD biomedical/chemical/temperature sensors, while embedding QDs in the top TiO₂ layer will increase the light extraction from the QD light emitting device, making our CPC a versatile optical coupling structure. Our CPC-QD structure is experimentally feasible and robust against the parameter perturbation in real fabrication.

Enhancing the fluorescence of perovskite nanocrystals (PNCs) will not only boost the development of perovskite light-emitting devices (LEDs), but also broaden their applications in various photoelectronic areas. However, an effective approach to flexibly enhance different emission colors with high enhancement factors is still desired. In this work, SiO₂ photonic crystals (PCs) are designed to couple with the radiative emission of PNCs. Blue, green, and red fluorescent PNCs emitting at 460, 517 and 620 nm are coated onto PCs with SiO₂ particle sizes of 200, 230, and 274 nm, respectively. Fluorescence enhancement factors of 22, 12, and 19 are acquired when the excitation power is 0.078 W. Moreover, the enhancement factor noticeably increases with the excitation power. The enhancement factor for blue PNCs is over 250 with an excitation power of 0.09 W. The enhanced fluorescence of PNCs will facilitate the fluorescence signal acquisition with low noise, which is favorable for optical sensing. As a proof of concept, we demonstrate that the luminescence temperature sensing capability of the PNCs on SiO₂ PCs is significantly boosted compared to that of the PNCs on glass.

This work develops a thermometer based on the fluorescence intensity ratio (FIR) of Sb-doped Cs ₂ NaInCl ₆ (Cs ₂ NaInCl ₆ :Sb).

A new method to control heat flux, called thermal surface transformation (TST), is introduced from transformation thermodynamics. Compared with transformation thermodynamics, TST has many advantage. First, there is no mathematical calculation during the whole process in TST (novel thermal devices can be designed graphically in a surface-to-surface way). Second, all thermal devices of various functions, shapes and sizes designed by TST only require one homogenous anisotropic thermal medium, i.e., thermal-null medium (TNM). With the help of the effective medium theory, TNM can be realized by layered copper and expanded polystyrene, whose performance on controlling heat flux by TST is verified by numerical simulations. Many examples are given, including thermal imaging devices, thermal unidirectional cloak, concentrator, rotator and thermal focusing devices.

We show a hybrid structure consisting of Si film with photonic crystal surface and random triangular gold grooves reflector at the bottom, which is capable of realizing efficient, broad-band, wide-angle optical absorption. It is numerically demonstrated that the enhanced absorption in a broad wavelength range (0.3–9.9 μm) due to the scattering effect of both sides of the structure and the created resonance modes. Larger thickness and period are favored to enhance the absorption in broader wavelength range. Substantial electric field concentrates in the grooves of surface photonic crystal and in the Si film. Our structure is versatile for solar cells, broadband photodetection and stealth coating.