Two-wavelength infrared responsive soft actuators composed of rare-earth-oxide particles composited in a thermoresponsive hydrogel have been constructed. Because Nd₂O₃ and Yb₂O₃ particles possess independent narrow infrared adsorption at 808 and 980 nm, respectively, the vicinity of the particles in the gel can be individually heated by irradiation at each adsorption wavelength, inducing a local volume phase transition. The wavelength-selective volume phase transition can be controlled based on the combination of the particles incorporated in the gels and the wavelength of the irradiation laser at the optimized water temperature. Only the alternatively correct combinations successfully induced selective local clouding at the irradiation spots in the gel sheets. The original transparency of the gel was immediately recovered by turning off the light. Furthermore, rod-shaped block gels with Nd₂O₃ and Yb₂O₃ particles separately arranged on the left and right sides at the bottom of the rods were prepared to demonstrate wavelength-selective bending motion. The correct light combination caused reversible bending motion of only the side of the rod gel with the corresponding adsorbed particles.

We demonstrate the fabrication of millimeter-sized single crystals of 0D-Cs₄PbBr₆ grown in a supersaturated solution consisting of organic solvents without HBr (aq). One of the precursors, CsBr, was dissolved in ethylene glycol (EG) mixed with dimethyl sulfoxide, which is a good solvent for the other precursor, PbBr₂. At a solvent ratio of 20 vol % EG, the solubility of cesium bromide decreased and the title compound, Cs₄PbBr₆, was selectively formed, whereas, with an EG ratio of 80 vol %, 3D-CsPbBr₃ was formed. A phase diagram (solubility curve) of Cs₄PbBr₆ in the mixed solvent containing 20 vol % EG was obtained by visually observing dissolution and crystal precipitation while changing the temperature. Because the solubility was proportional to the temperature, the solubility curve demonstrated an upper critical solution phenomenon. The solubility near the boiling point of the solution (150 °C) was approximately 0.14 M. A single crystal of Cs₄PbBr₆ was formed by growing a seed crystal in a supersaturated solution on the low-temperature side of the solubility curve. X-ray analysis established the crystal structure; a fluorescence emission at 520 nm with a full width at half maximum of 20 nm confirms the composition of the single crystal to be Cs₄PbBr₆.