This work reports on a combinational methodology to CaWO4 nanocrystals of controllable particle sizes for comprehension of particle size dependences of physical properties. Citric acid as a capping molecule restricted the growth of CaWO4 nanocrystals and gave a small particle size of 3.6 nm at room temperature at pH 8, while large particle sizes or the absence of CaWO4 nanocrystals were always observed when the pH value was higher or lower than 8. Hydrothermal treatments over 3.6 nm CaWO4 at high temperatures led to a systematic increase in particle sizes. X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and UV−vis spectroscopy were employed to study the particle size dependences of properties including lattice dimensions, vibrational variations, and transition energies. It is found that, with particle size reduction, CaWO4 nanocrystals showed a lattice expansion, an enhanced structural symmetry, and a red shift in the Au phonon mode. A drastic blue shift of the electronic absorption bands was also observed for the transition of 1A1 → 1T1 in CaWO4 nanocrystals at small sizes, which was explained by taking into account the quantum confinement effect and the enhanced ionicity of W−O bonds.

A fiber Mach-Zehnder interferometer (MZI) sensor, novel to our knowledge, based on a single "S"-like fiber taper has been fabricated via applying nonaxial pull in fiber tapering by a fusion splicer. The typical feature size of the structure has a length of 660 μm and the axial offset of 96 μm. This S fiber taper MZI has a refractive index (RI) sensitivity of 1590 nm/refractive index unit in the RI range of 1.409-1.425 and a strain sensitivity of about -60 pm/microstrain, which is 30 times higher than that of the normal two-taper-based MZI sensors.

We predict the existence of a self-localized solution in a nonresonantly pumped exciton-polariton condensate. The solution has a shape resembling the well-known hyperbolic tangent profile of the dark soliton, but exhibits several distinct features. We find that it performs small oscillations, which are transformed into 'soliton explosions' at lower pumping intensities. Moreover, after hundreds or thousands of picoseconds of apparently stable evolution the soliton decays abruptly, which is explained by the acceleration instability found previously in the Bekki-Nozaki hole solutions of the complex Ginzburg-Landau equation. We show that the soliton can be formed spontaneously from a small seed in the polariton field or by using spatial modulation of the pumping profile. PACS numbers: 71.36.+c, 03.75.Lm, 42.65.Tg, Microcavity exciton-polaritons are remarkable quasiparticles, suitable for the study of degenerate bosonic states at a few Kelvin or even at room temperature [1][2][3]. The combination of the photonic component with its extremely small effective mass, and strong interparticle interactions mediated by the excitonic component, makes it possible to investigate directly numerous phenomena of fundamental interest, including superfluidity or topological defects [4], and opens a path to applications such as ultralow threshold lasers or efficient information processing [5].Recently, there has been a strong interest in the existence and dynamics of solitons in polariton systems [6][7][8][9][10]. Solitons are self-localized, shape-preserving solutions of nonlinear partial differential equations, existing in a wide range of physical, biological and chemical systems [11]. They can be thought of as natural modes of nonlinear wave equations, and play the role of attractors that are approached by the system that is placed sufficiently close to them. As such, they are natural candidates for information carriers over long distance links [12]. In polariton systems, due to significant losses solitons are inherently dissipative, which means that the balance between loss and pumping is an important dynamical constraint. Such dissipative solitons [13] are known to be qualitatively different from the ones present in Hamiltonian systems. They may exist as quasi-stationary states, evolving in a complicated and often chaotic manner [14].So far, most of the studies of polariton solitons concentrated on the case of resonant external pumping, where the phase and momentum of polaritons under the pumping spot is directly imposed by the laser. Both bright [6] and dark [7,8] solitons were predicted and observed in experiments, as well as half-solitons with nontrivial spin structure [15]. On the other hand, nonresonant pumping allows to create a degenerate bosonic state with a spontaneously chosen phase profile. In this context, bright self-localized states [9, 10] and gap states [16] were recently found in the case of inhomogeneous pumping.In this Letter, we show that dark dissipative solitons (or heteroclinic holes) can be created in a no...