Resonance is the coincidence between the frequencies of two oscillations, which results in the increase of their intensity. Half a century ago, an Italian theoretical physicist Hugo Fano described a special type of resonance with an asymmetric profile arising from the interference of two wave processes. Since then, the Fano resonance has been actively used in photonics, for example, to create fast optical switches, which are elements of photonic integrated circuits. Reducing such switches to nanoscale will lead to a significant boost in the photonic chips’ performance by integrating a huge number of elements in one device.
Together with their colleagues from Sweden, Australia, the United States, and Lithuania, researchers from ITMO University have made a big breakthrough by discovering the Fano resonance in perovskite nanoparticles. They also managed to gain control over the resonance spectrum for an array of inorganic nanoparticles. To do this, the scientists proposed a new method of tuning the nanoparticles’ radiation. Instead of synthesizing several different types of particles, the researchers suggested changing the composition of one fully-formed particle through special chemical treatment. As this adjustment is reversible, it can be repeated many times without changing the stability of the particles and the intensity of their radiation.
"We conducted experiments with single organo-inorganic perovskite nanoparticles, as well as with an unordered array of completely inorganic nanoparticles dispersed in the polymer matrix. We managed to register Fano resonances in both cases, but the reversible tuning was possible only for inorganic particles. Their composition includes bromine anions, and during the adjustment we succeeded in changing the bromine atoms to the chlorine atoms through a reversible reaction. This makes it possible to shift the emission spectrum of particles to 100 nm in the range of 420-520 nm. Organo-inorganic nanoparticles proved to be unsuitable for a similar adjustment of photophysical properties due to the presence of organic cations in their structure," says Anatoly Pushkarev, research associate at the Laboratory of Hybrid Nanophotonics and Optoelectronics of ITMO University.
According to the researchers, the proposed method for tuning the emission spectrum of the studied perovskite nano-antennas is universal. It can be applied to other inorganic nanostructures based on lead halides. These findings make it possible to develop complex optoelectronic devices functioning on a chip with the minimum amount of nanoparticles. These miniature devices can be used in data transmission and processing, as well as for sensing.
"The results we obtained are promising not only in terms of developing photonic integrated circuits. The reconstruction of the nanoparticles array emission spectrum and the change in the position of the Fano resonance in their optical absorption spectrum can be used, for example, to determine the concentration of hydrogen halide vapor (HCl, HBr, HI) in the medium," says Ekaterina Tiguntseva, PhD student at ITMO University’s Faculty of Physics and Technology.
