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The ZnS: Ho3+, Yb3+, Mn2+ nanomaterials fabricated by the co-precipitation method have the zinc-blende structure with the crystallite size about 90 ∼ 100 nm. The X-ray diffraction (XRD), the scanning electron microscope (SEM) and the transmission electron microscope (TEM) characterizations confirm that the doping of the Mn2+ has less effect on the structure of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials. With the excitation of a 978 nm laser, the upconversion (UC) emissions of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials include two emission bands located at 551 and 664 nm, which correspond to the transitions 5F4 (5S2)→5I8 and 5F5→5I8 of the Ho3+ ions. The UC emission characterization confirms that the UC emission of the ZnS: Ho3+, Yb3+ nanomaterials can be modulated by the doping of the Mn2+ ions, the increase of the incident laser power and the change of the laser pulse-width. The red emission of the ZnS: Ho3+, Yb3+ nanomaterials particle will increase significantly with the incorporation of the Mn2+ ions. The incident laser power and the laser pulse-width also can modulate the intensity ratio G/R of the green to the red. With the increase of the incident laser power, the emission intensity ratio G/R will also increase. With the increase of laser pulse-width from 0.2 to 0.8 ms, the above intensity ratio G/R will decrease significantly. The modulation between the green and red emission is due to the energy transfer from the 5F4 (5S2) state to the 5F5 state of the Ho3+ ions through the state 4T1 of the Mn2+ ions. [ABSTRACT FROM AUTHOR]

The waveguide based on the honeycomb photonic crystal has propagating modes for both the TE and TM polarizations. The group index-normalized frequency curves are U-shaped for the two polarizations. The average group index of the TE mode is approximately 3, while the average group index of the TM mode is over 10, which implies that the TM mode is a slow light mode. With the shift value 0 [less than or equal to] [delta]x [less than or equal to] 0.025a, the group index is over 10 and the normalized delay-bandwidth product is from 0.316 to 0.349, which is ideal for the slow light mode of the TM polarization. In the group velocity dispersion of the waveguide, there is a very large 'zero' dispersion region for both the TM and TE modes, which is far larger than that of other photonic crystal waveguides. The TM mode of this kind of waveguide structure is a slow light mode with wide bandwidth and a large 'zero' dispersion region. [c] 2010 Optical Society of America OCIS codes: 310.2790, 160.3918.

In this paper, a Fabry-Perot optical modulator fabricated by surface micromechanical technique is presented. The modulator is optimized for a wavelength of 1.3 [micro]m and is intended for a fiber-to-the-home system. The actuation voltage of the modulator is measured to be 10-25 V. The optical modulator has a series of resonant frequencies determined from the device structure. When the modulator is driven by a sinusoidal signal, the output frequency will be doubled. For a driving signal greater than a certain value, the oscillation amplitude of the membrane will exceed [lambda]/4, resulting in an ultrasaturation phenomenon. [641] Index Terms--Fabry-Perot modulator, MEMS, optical modulator.

Recently, 2D materials have emerged in the field of light‐to‐heat conversion. However, it is urgent to find a simple and effective method to reduce the light reflectivity of the 2D surface to improve the light‐to‐heat conversion efficiency. A 2D nano‐self‐assembly material coating (NiS2@Ti3C2) realized by a simple hydrothermal method, which enables unique‐sized nano‐NiS2 crystals and 2D Ti3C2–MXenes to self‐assemble on a 3D scale, is innovatively proposed. Such a preparation method can construct a unique multilayer structure for multistage diffuse reflection of incident light, so that the MXene nanomaterial can achieve a light absorption rate of >90% in a wide spectral range. The composite is theoretically verified through optical simulation and first principles, and a higher light‐to‐heat conversion performance is achieved experimentally (61.7 °C surface equilibrium temperature, 1 sun). Compared with other similar materials, the assembled MXene seawater steam generator achieves a higher steam generation rate (1.27 kg m−2 h−1) and light‐to‐heat conversion efficiency (83.84%) under 1 sun. This material structure can maximize MXene active materials' utilization and provide ideas for modifying other 2D photothermal materials. [ABSTRACT FROM AUTHOR]

The YVO4 nanomaterials doped with the Yb3+/Tb3+/Eu3+ ions and their mixture with the Au nanoparticles are synthetized with a classical sol‐gel method. With the excitation of a 975 nm laser, both the doped YVO4 sample and the corresponding mixture sample have a series of upconversion emission peaks of Eu3+ and Tb3+, which includes the 5D0→7Fj transitions of the Eu3+ ions and the 5D4→7Fj transitions of the Tb3+ ions. The slope values of the log‐log plots of laser power dependence for the upconversion emission intensities range from 1 to 2, which confirms that the upconversion process is a two‐photon process. With the plasmon coupling, the slope value for the power dependence of the magnetic dipole transition 5D0→7F1 of the Eu3+ ions decreases from 1.4 to 1.1, while it increases for other electric dipole transitions. Because of the plasmon coupling, the emission peak of the Eu3+ at about 2.095 eV decreases significantly and almost cannot be observed. Meanwhile, the emission peak of the Tb3+ at about 2.113 eV increases significantly and becomes the main emission peak in the yellow band. This phenomenon confirms that there is different mechanism for the magnetic and electric dipole emission with the plasmon coupling. [ABSTRACT FROM AUTHOR]