• Nanophotonics
 
• Research update

Phase-changing material generates vivid tunable colours

02 Dec 2025 Tami Freeman

Switchable camouflage A toy gecko featuring a flexible layer of the thermally tunable colour coating appears greenish blue at room temperature (left); upon heating (right), its body changes to a dark magenta colour. (Courtesy: Aritra Biswa)

Structural colours – created using nanostructures that scatter and reflect specific wavelengths of light – offer a non-toxic, fade-resistant, and environmentally friendly alternative to chemical dyes. Large-scale production of structural colour-based materials, however, has been hindered by fabrication challenges and a lack of effective tuning mechanisms.

In a step towards commercial viability, a team at the University of Central Florida has used vanadium dioxide (VO2) – a material with temperature-sensitive optical and structural properties – to generate tunable structural colour on both rigid and flexible surfaces, without requiring complex nanofabrication.

Senior author Debashis Chanda and colleagues created their structural colour platform by stacking a thin layer of VO2 on top of a thick, reflective layer of aluminium to form a tunable thin-film cavity. At specific combinations of VO2 grain size and layer thickness, this structure strongly absorbs particular frequency bands of visible light, producing vivid colours.

The key enabler of this approach is that, at a critical transition temperature, VO2 reversibly switches from an insulating to a metallic state, accompanied by a change in its crystalline structure. This phase change alters the interference conditions in the thin-film cavity, thereby modifying the reflectance spectrum and the perceived colour. Controlling the thickness of the VO2 layer enables the generation of a wide range of structural colours.

The bilayer structures are grown via a combination of magnetron sputtering and electron-beam deposition, techniques compatible with large-scale production. By adjusting the growth parameters during fabrication, the researchers could broaden the colour palette and control the temperature at which the phase transition occurs. To expand the available colour range further, they added a third ultrathin layer of high-refractive index titanium dioxide on top of the bilayer.

Inkjet technique prints rainbow of structural colours from a single transparent ink

The researchers describe a range of applications for their flexible coloration platform, including a colour-tunable maple leaf pattern, a thermal sensing label on a coffee cup, and tunable structural coloration on flexible fabrics. They also demonstrated its use on complex shapes, such as a toy gecko with a flexible, tunable colour coating and an embedded heater.

“These preliminary demonstrations validate the feasibility of developing thermally responsive sensors, reconfigurable displays, and dynamic colouration devices, paving the way for innovative solutions across fields such as wearable electronics, cosmetics, smart textiles, and defence technologies,” the team concludes.

The research is described in Proceedings of the National Academy of Sciences.

Tami Freeman is an online editor for Physics World

from physicsworld.com    12/12/2025