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A variety of mechanoluminescent (ML) materials have recently reinvigorated studies of luminescence activated by mechanical stress, but few practical applications have been demonstrated due to the destructive nature of the process. To overcome these shortcomings, elastico-mechanoluminescent (elastico-ML) materials, which generate luminescence under elastic deformation, have been suggested with a view to their use in practical devices. However, the weak brightness and limited white colour expression of these materials must be resolved before they can be employed in practical applications. Here, we report a wind-driven ML device that produces significant brightness and emits warm/neutral/cool white light over a range of colour temperatures from zinc sulphide (ZnS) microscopic particles embedded in a polydimethylsiloxane (PDMS) composite. Harnessing wind-activated mechanoluminescent devices in practical displays or lighting systems could pave the way to new environmentally friendly lights, which reduce energy waste and promote sustainability. Broader context Mechanically driven light generation is an exciting and under-exploited phenomenon with a variety of possible practical applications. Mechanoluminescence (ML) has potential applications in colourful displays and white-light sources driven by vibrating mechanical actions. However, the related research has suffered from the difficulty in obtaining a strong, repeatable signal, so enhancing ML intensity has not been a major area of focus. Weak brightness and limited white colour expression of ML must be resolved with a view to its use in practical ML displays or ML light sources. Here we report a new wind-driven ML device that produces signicant brightness and emits light over a range of tunable white colours. A patterned, colourful ML driven by wind was also demonstrated. Harnessing wind-driven ML in practical lighting systems could pave the way to new environmentally friendly lights based on wind motion, to cut down energy waste and promote sustainability.

The prospective application of luminescence to imaging devices is shown using a combination of color-tunable and patternable mechanoluminescent materials. A white light source is demonstrated by using an alternative color tuning method, induced under high vibration conditions. As the implementation is fairly straightforward, it is expected that the present results will find a number of potential uses in current industrial applications.

A cholesteric liquid crystal (CLC) is a self-assembled photonic crystal formed by rodlike molecules, including chiral molecules, that arrange themselves in a helical fashion. The CLC has a single photonic bandgap and an associated one-colour reflection band for circularly polarized light with the same handedness as the CLC helix (selective reflection). These optical characteristics, particularly the circular polarization of the reflected light, are attractive for applications in reflective colour displays without using a backlight, for use as polarizers or colour filters and for mirrorless lasing. Recently, we showed by numerical simulation that simultaneous multicolour reflection is possible by introducing fibonaccian phase defects. Here, we design and fabricate a CLC system consisting of thin isotropic films and of polymeric CLC films, and demonstrate experimentally simultaneous red, green and blue reflections (multiple photonic bandgaps) using the single-pitched polymeric CLC films. The experimental reflection spectra are well simulated by calculations. The presented system can extend applications of CLCs to a wide-band region and could give rise to new photonic devices, in which white or multicolour light is manipulated.

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