This study reports a synthesis by the sol−gel method of stable and size-controlled ZnO quantum dots (QDs) embedded into a SiO 2 matrix in the diameter range of 2.7−5.5 nm with strong visible emission in the blue-green region. X-ray diffraction and selected area electron diffraction techniques evidence a wurtzite structure of the prepared ZnO QDs. Transmission electron microscopy investigation highlights that the ZnO nanoparticles produced in methanol solution have a nonuniform shape. Addition of tetraethyl ortho-silicate (TEOS) in the solution at different times blocks the nucleation of the QDs and allows the control of the QD size due to a SiO 2 capping. Moreover, Fourier transformed infrared analysis and X-ray photoelectron spectroscopy (XPS) were used to show the ZnO QD composition and to confirm their incorporation into the SiO 2 matrix by the creation of a Zn−O−Si crossing link. A strong UV band and a weak visible band are revealed at room temperature by photoluminescence (PL) measurement for pure ZnO nanoparticles, whereas, when TEOS is added, the UV band is quenched and a strong visible emission in the range 400−650 nm is enhanced. PL spectra fitting, using Gaussian curves, shows three possible transitions that induce the visible emission. This PL study is correlated to the quantitative XPS study combined with a simple model describing the nanoparticles giving the relative amount of species involved in this emission mechanism. These QDs are then used to manufacture humidity sensors. Indeed, electrical measurements show a high sensitivity to the relative humidity. Moreover, a remarkable enhancement of the sensor performance is observed when the ZnO QD size decreases.

Standing Lamb waves in vibrating plates enable haptic interfaces. If the out‐of‐plane displacement of these waves exceeds 1 µm at frequencies above 25 kHz, a silent friction modulation can be created between a human finger and a vibrating plate. A fully transparent friction‐modulation haptic device based on a piezoelectric thin film is demonstrated. The antisymmetric Lamb mode induced at 73 kHz allows for a functional performance that fulfills all conditions for practical use. Out‐of‐plane displacement reaches 2.9 µm when 150 V unipolar voltage is applied. The average transmittance of the whole transducer reaches 75%. The key points of this technology are: 1) a thin HfO2 layer between lead zirconate titanate film and substrate that prevents chemical reaction between them; 2) the efficient integration of transparent indium tin oxide electrodes and solution‐derived piezoelectric lead zirconate titanate thin film onto optical‐grade fused silica; and 3) the use of a transparent insulating layer made of SU‐8 photoresist.