Color-changing light-emitting fibers woven into fabric enable flexible, pixel-level displays for smart textiles, opening new possibilities for wearable communication.
(Nanowerk Spotlight) Imagine a jacket that flashes transit directions across its sleeve, or a scarf that displays spoken phrases in real time for someone who cannot speak. Within two or three years, smart textiles capable of dynamic, multicolor visual communication could move from concept to commercial prototype—not by embedding rigid displays into fabric, but by weaving the display directly into the threads themselves. These fabrics wouldn’t rely on printed circuits or mounted LEDs. Instead, they would use specialized fibers that emit and modulate light on demand, pixel by pixel, through simple electrical inputs. The foundation for this shift lies in new materials and device architectures that merge light emission and color filtering in a single fiber, with enough durability to be stitched, stretched, and worn like any other fabric.
This direction builds on a decade of efforts to develop luminescent fibers for wearable displays. Conventional electroluminescent fibers—threads that glow when powered—have shown promise for embedding light into textiles. However, they have a fixed color and can only display pre-defined patterns. More flexible display functions, like full-color output or real-time pixel control, have remained out of reach due to technical constraints. Attempts to vary emission colors or overlay filters have faced challenges such as slow response time, high energy demands, or complex fabrication steps incompatible with textile-scale deployment.
In a study published in Advanced Materials (“Coaxial Electroluminochromic Fibers with Dynamic RGB Switching for Pixelated Smart Textiles”), a team at Tsinghua University introduces a coaxial fiber architecture that combines electroluminescent and electrochromic functions. These fibers can emit blue or green light from within and filter that light through an outer polymer shell whose transparency and color shift under low-voltage control. Each fiber acts as a tunable light source, capable of switching between multiple colors and brightness levels with electrical precision. By integrating these fibers into woven fabrics, the researchers demonstrate pixel-level display capabilities with full mechanical flexibility and long-term stability, laying the groundwork for high-resolution, soft, wearable displays.
Structure and mechanism of electroluminochromic (ELC) fibers and textiles. A) Schematic illustrations of the emission core and the optical filter shell within an ELC fiber. B) Conceptual image of an ELC textile and its application scenarios in communication displays. C) Luminescence spectra were obtained with a white backlight and a P3MT optical filter in the oxidation, intermediate, and reduction states. D) Luminous performances characterized by five indicators, namely color gamut, visible angle, switching speed, manufacturability, and flexibility for this study, (1) display textiles, (2) fiber-shaped electroluminescence cells, (3) multicolor EL fibers, (4) electroluminescent & thermochromic fibers, respectively. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The ELC fiber is built around a carbon nanotube fiber (CNTF), selected for its electrical conductivity, mechanical strength, and compatibility with coating processes. The core is coated with phosphor particles embedded in a polyurethane matrix, enabling it to emit blue or green light when excited by an electric field. A high-dielectric material, barium titanate, is also included to stabilize the electric field and prevent breakdown of the insulating layer. This configuration ensures stable and bright emission even under mechanical deformation or environmental exposure.
Surrounding the EL core is a transparent insulating layer made of PDMS, a silicone-based polymer. This insulation physically separates the EL and EC systems, preventing interference between the high-frequency AC driving the core and the low-voltage DC used for color modulation. On top of this insulation, the fiber is coated with a thin transparent electrode layer of PEDOT:PSS, followed by an electrochromic layer made of poly-3-methylthiophene (P3MT). The outermost layer is a gel polymer electrolyte that enables ion movement necessary for the EC reaction. Two additional CNTFs are placed parallel to the fiber as counter electrodes to establish a uniform electric field across the EC layer.
When a voltage is applied to the EL core, it emits light based on the properties of the embedded phosphors. For blue emission, copper-doped zinc sulfide crystals are used, while green emission is achieved by adding aluminum or chlorine. The EC layer, controlled by a separate DC voltage, changes its optical transmittance depending on its redox state. In its oxidized form, P3MT allows more light to pass through. In its reduced state, it absorbs more light, effectively dimming the fiber or shifting the perceived hue. The researchers demonstrated three distinct emission states—dark, intermediate, and bright—corresponding to DC voltages of –2.0, 0.6, and 2.5 V, respectively.
Importantly, the ELC fibers maintained performance under conditions relevant to textile use. They were tested for mechanical flexibility by knotting and twisting, and for environmental stability by immersion in water and ethanol. Luminescence remained consistent, and cycling tests showed stable performance over 10,000 switching cycles. These tests confirm that the fibers are suitable for integration into wearable systems that must endure repeated deformation and exposure to moisture.
To demonstrate practical use, the team constructed a prototype display fabric using an array of ELC fibers. The textile was woven such that horizontal ELC fibers intersected with vertical CNTF electrodes. At each crossing point, a drop of gel polymer electrolyte created a localized EC modulation region—essentially a pixel. These junctions could be addressed independently, with the AC signal activating the EL emission and the DC input controlling the EC layer’s optical state. This setup allowed the researchers to display simple pixel patterns, with each pixel capable of emitting different brightness levels or colors.
The use of coaxial architecture allows the emission and filtering components to be optimized separately. For instance, the researchers explored other electrochromic materials like polypyrrole, although it provided less precise color modulation than P3MT. The design is also compatible with different phosphors, including white-light emitters, suggesting that full-spectrum displays could be developed by combining the appropriate emission sources with tunable EC filters.
The electrical performance of the fiber is also tunable. Increasing the AC voltage enhances the brightness of the EL emission according to an exponential relationship. However, there is a diminishing return at high voltages, so a balance must be struck between brightness and power consumption. The authors provided a quantitative model for this relationship, which can guide future optimization.
Fabrication of the fibers relies on dip-coating techniques carried out in air, which simplifies the process and makes it suitable for scaling up. The entire system is compatible with roll-to-roll manufacturing and existing textile weaving methods. This lowers the barrier for commercial development and supports integration into real-world garments or accessories.
The study presents a coherent approach for overcoming the limitations of fixed-color EL fibers by adding a dynamically tunable optical filter in the form of an electrochromic shell. By physically isolating and independently controlling the emission and filtering layers, the coaxial design introduces a new method for generating multicolor, pixel-addressable light sources directly in flexible fibers. This work establishes a technically grounded strategy for developing wearable display systems that combine color control, mechanical robustness, and scalability, addressing several longstanding challenges in electronic textiles.
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
