From microscopes to fibre optic cables, the ability to control light underpins many modern innovations. Today, advanced optical components are often smaller than the eye can see; for example, television screens, which formerly projected images using fist-sized cathode ray tubes, now rely on light-emitting layers of polymers thinner than a human hair.
For Zhaogang Dong, a Principal Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE), perovskites are an especially intriguing class of prospective materials for future screens. When shaped into perovskite quantum dots (PQDs)—tiny crystals under 20 nanometres wide—they become exceptionally good at absorbing and emitting light.
“These properties make PQDs pivotal in photovoltaics, enabling more effective solar panels that lessen our dependence on fossil fuels,” said Dong. “They can also enhance the brightness and vibrancy of light-emitting diode (LED) displays for clearer, more energy-efficient screens.”
However, PQDs only emit light in a narrow spectrum of wavelengths, which limits what they can be used for. While that spectrum can be widened by physically or chemically altering these nanocrystals, “those approaches typically cause poor colour saturation and quenched light intensity, or need sophisticated setups,” Dong added.
To open up PQDs for more diverse applications, Dong and colleagues from IMRE formed a multidisciplinary team with researchers from A*STAR’s Singapore Institute of Food and Biotechnology Innovation (SIFBI); the National University of Singapore (NUS); Nanyang Technological University, Singapore; the University of Sheffield, UK; and Pennsylvania State University, US.
Together, they designed an optical nanoantenna array: a mat of tiny paired silicon bristles, each capable of resonating with light at the nanoscale. With the base of each ellipse-shaped bristle coated in PQDs, the nanoarray was designed to exploit a phenomenon known as quasi-bound-states-in-the-continuum (q-BIC) to ‘trap and release’ light particles (aka photons) emitted by PQDs.
“These optical nanoantennas interact with light in a way similar to how a radiofrequency antenna receives radio signals,” said Dong. “By tuning their resonance, we can precisely adjust the PQD emission spectrum without altering the PQDs themselves.”
The researchers fabricated several PQD-coated q-BIC nanoarrays with various geometries, then compared the effect of those variations on the nanoarrays’ light emissions. They found that by exploiting the variability of q-BIC resonance energies, the nanoarrays could not only shift PQD emissions in a 39 nm range, but increase their intensity 21-fold. Previously reported photonic antenna designs had achieved a maximum shift of 8 nm—at the cost of a five-fold reduction in intensity.
The team aims to incorporate their findings into tuneable single-photon emitters for daylight quantum communication systems, which would pave the way for more robust data security tools.
Dong credited NUS’ Cheng-Wei Qiu and Zhi-Kuang Tan for their contributed expertise in structured light, nanophotonic cavities and PQD synthesis, as well as the University of Sheffield’s Graham Leggett and A*STAR Research Attachment Programme (ARAP) scholar Eveline Csanyi for their similar contributions in nanoscale interface chemistry.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE) and Singapore Institute of Food and Biotechnology Innovation (SIFBI).