In this study, we report an Er-doped quaternary piezoelectric semiconductor CaZnOS:Er3+ which shows both mechanoluminescence and upconversion luminescence properties. Under mechanical stimulation, green light emission can be observed by the naked eye from a flexible film fabricated by encapsulating CaZnOS:Er3+ particles between two polyethylene glycol terephthalate substrates. The integral emission intensity is proportional to applied pressure, making CaZnOS:Er3+ suitable for dynamic pressure sensing applications. Moreover, the doped sample also shows bright visible emission with near-infrared (980 nm) excitation. The fluorescence intensity ratio between two upconversion emission bands corresponding to 2H11/2, 4S3/2 → 4I15/2 transitions of Er3+ is sensitive to the variation of temperature. As a multifunctional optical material, CaZnOS:Er3+ could be used to not only visualize two-dimensional pressure distribution, through mechanically induced emission, but also sense temperature via the upconversion (UC) luminescence. This work provides a novel kind of multifunctional luminescent material for the development of integrated and coupling devices.

•A flexible, well patterned, vertical aligned n-ZnO NW/p-PEDOT:PSS LEDs array is firstly demonstrated.•The piezo-phototronic effect was demonstrated in the n-ZnO NW/p-PEDOT:PSS LEDs array for the first time.•The emission intensity of the ZnO nanowire/p-polymer LEDs can be enhanced by applying an external strain owing to the piezo-phototronic effect.Flexible optoelectronic device arrays are critically desirable for next-generation digital display, seamless integration of optoelectronics with biomedical and human–machine interactive systems and many other applications. Here we report a flexible patterned ZnO nanowire/PEDOT:PSS LEDs array with very high light-emitting uniformity. A near band edge emission centered at 400 nm and a broad defect-related emission covering the range from 450 to 780 nm is observed in the electroluminescence spectra. Both anneal and H2O2 treatment of the ZnO NWs and the optimal thickness of PEDOT:PSS can improve the performance of the as-fabricated device. Furthermore, we demonstrate that the emission intensity of the ZnO nanowire/p-polymer LEDs can be enhanced by applying an external strain owing to the piezo-phototronic effect, which reduces the barrier height for hole transport, leads to an improved balance between electron contributed current and hole contributed current, owning to the piezoelectric charges on the ZnO side created by applying local strain. The simple fabrication process and excellent properties of the device pave the way to cost-efficient LED technology for potential applications in high-resolution optoelectronic device, biomedical implanted devices, artificial electronic skin and smart sensor systems.

Nitrogen-doped TiO2 nanotubes were synthesized by annealing of the anodized titania nanotubes with ammonia at the temperature of 500 °C. The ordered structure of titania nanotubes maintained after the nitrogen doping process, as is evidenced by SEM observations. Detailed structural analysis revealed that the phase transformation temperature of titania nanotube from anatase to rutile is decreased after nitrogen doping. The XRD patterns of nitrogen-doped titania exhibit an increased peak intensity and a decreased FWHM in the (110) peak of rutile in comparison with those of undoped titania under the same annealing conditions, indicating that nitrogen doping may have facilitated the phase transition at the annealing temperature of 500 °C, which is in consistence with the analysis of Raman spectra as the comparison of A1g and Eg Raman peaks of rutile in the nitrogen-doped and undoped titania.

•A lightweight, cost-effective and scalable strain sensor with excellent performance is developed by utilizing the micro-cracked metal thin film by combining the overlap modal with tunnel effect of the adjacent cracks;•Detection of tiny strain of human non-joints, physiological pulse wave, canthus motion and any biological associated skin deformation is demonstrated;•Mapping of strain distribution and anti-interference voice recognition system using this sensor pave the way to practical applications in smart sensor system and wearable electronics.The poor detecting limit and attenuated sensitivity to tiny strain of a strain sensor retard their development toward practical applications ranging from wearable electronics, human healthcare monitoring to smart sensing system. Here, a strain sensor with high sensitivity to tiny strain, high flexibility, fast response and good stability is developed utilizing the micro-cracked metal thin film based on a novel working principle of combining the overlap mode with tunnel effect of the adjacent cracks. Monitoring of human motions and physiological signals as well as anti-interference voice recognition based on the sensor is demonstrated, showing its potential applications in wearable electronics, human healthcare monitoring and smart sensing system.Large-scale strain sensor with attributes of high sensitivity, highly flexibility, fast response and good stability is developed utilizing the micro-cracked metal thin film to satisfy practical applications in detection of human non-joint areas tiny strain and non-interference voice recognition, representing an important step toward design and applications of the strain sensor.