Scientists from the Beijing Institute of Technology have revealed a colloidal quantum dot (CQD)-based infrared-to-visible upconverter that transforms the infrared spectrum into full color, allowing people to ‘see’ the infrared in the visible light spectrum.
The research team behind the novel invention said their upconverter can be used in eyeglasses to improve human vision and for augmented reality (AR) applications. They also reported a successful implantation of an upconverter in mice, opening the possibility of an implantable photoreceptor to repair or improve vision in human eyes.
Attempts to Convert Infrared to Full Color Face Limitations
In a published study detailing the novel, full-color IR glasses, the human eye is “inherently blind” to infrared radiation. Although IR radiation interacts with the retina, infrared wavelengths lack the energy to trigger the photoisomerization of the retinal chromophore that lets people distinguish colors. As a result, humans don’t have visual access to over half of the solar spectrum.
Still, the researchers write, “harnessing this imperceptible radiation is critical, as infrared perception unlocks a vast reservoir of inaccessible information.” For example, this added visual information enables critical functions in other animals, such as navigation in darkness or detecting predators and prey from their heat. Still, they observe that our natural visual-light spectrum vision is “utterly inadequate” to access this information that so many animals rely upon.
In their study, the researchers highlight recent advances in accessing the IR spectrum, including “ocular injectable photoreceptor-binding upconversion nanoparticles” that convert infrared light into visible emissions. Other studies have also evaluated wearable lenses with nonlinear upconversion projecting infrared-transformed visible light onto the cornea and photovoltaic nanowire networks.
Although these approaches achieved some IR sensitivity, the study authors said they remain “fundamentally constrained” to narrow near-infrared (NIR) spectral response. These prior efforts also relied on high-intensity laser excitation that the team notes is “incompatible with natural infrared radiation.” The result is a “mostly monochromatic output” lacking infrared spectral discrimination in full color.
Subtle IR Wavelength Variations Facilitate Upconversion
For their new approach, the research team investigated a mercury telluride (HgTe) CQD-based infrared-to-visible upconverter. They note that this material combination leverages the material’s “quantized energy level states” in synergy with a separate, dual-emissive-layer organic light-emitting diode (OLED).
Specifically, the engineered layers captured IR photons in strategically engineered hole-trapping barriers. The team explains that this “allows for subtle differentiation of infrared input by tuning the emitted visible color and luminance” based on infrared wavelength and intensity.
“This upconversion yields a discrimination sensitivity to subtle infrared variations exceeding two orders of magnitude higher than conventional single-color modes, capitalizing on the human eye’s intrinsic superiority in chromatic differentiation over simple luminance contrast,” they explain.
To test their material’s IR upconversion ability, the researchers designed a pair of lightweight (23 grams) semi-transparent wearable eyeglasses. The team said these tests were a success, achieving “high-resolution infrared imaging” derived from the infrared spectral information. However, instead of monochrome, the research team said that data is displayed as full-color visible patterns directly onto the retina, “enabling intuitive infrared vision without obstructing natural sight.”
Surpassing the Evolutionary Boundaries of Biological Photoreception
Although the current version of the full-color, infrared-capable glasses is still in the development stages, the team said the technology could lead to advancements in visual prosthetics, augmented reality (AR), and “navigation under environmental conditions where normal sight is degraded.”
Following the successful validation in mice, the team said their technology could also serve as the technological basis for an implantable new-generation retinal photoreceptor. In that design, the team said an implanted device could transform infrared light into visible light emissions “that stimulate light-sensitive proteins on retinal neurons to bypass damaged photoreceptor cells and potentially restore visual function across both the visible and infrared spectra.”
“By surpassing the evolutionary boundaries of biological photoreception, this technology paves the way for next-generation visual prosthetics, high-fidelity augmented reality, molecularly sensitive substance identification, and robust navigation in degraded visual environments,” they conclude.
The study “Multispectral infrared-to-full-color upconversion expanding human vision” was published in Science Advances.
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org