Structural disorder found to amplify photoluminescence and electronic Raman scattering
A team of researchers from Kazan Federal University, ITMO University and Skoltech found that delocalization of optical near-field enables to unravel a number of fundamental mysteries in perovskite photonics, such as: 1) enhanced photoluminescence (PL) of quantum dots in glass matrixes, 2) PL/Raman blinking effect, 3) enhanced photoluminescence when phase transitions, 4) single-photon anti-Stokes photoluminescence under sub-band pump, 5) low-frequency Raman peak, 6) super-photoluminescence and lasing in nanocrystals.
"In the study, published in Advanced Science, the scientists theoretically and experimentally demonstrated the instrumental role of optical near-field for light-matter interactions in systems with "crystal-liquid" duality. Delocalization of the optical near-field allows light to better interact with optical heterogeneities which can either be intrinsic as in perovskites (for example, point defects or benign twin domains), or fabricated by destructuring of crystals, resulting in the formation of quantum dots. In the work, destructuring of a CsPbBr3 perovskite was fulfilled through DC electric pulses that generate electroluminescence. A near-field photon possessing expanded momentum interacts with an electron trapped by static/dynamic defects in the as-prepared crystal. The authors revealed that if a disordered crystal contacts the bulk crystal then a 2D disorder-order interface occurs on which enhanced photoluminescence and electronic Raman scattering are observed. Topological structures "disorder-order" represent dual systems "crystal-liquid" exhibiting long-range order but local disorder. The interaction of light with such a structure is enhanced due to a cascaded mechanism resembling "the matreshka principle", light is localized in larger structures that excite the optical field in smaller structures, and so on. Ultimately, the optical far-field couples to optical heterogeneities and increases the refractive index of medium. Naturally occurring "crystal-liquid" media include not only perovskites, which represent a long-range network of coupled octahedra, but also highly associated liquids, high-entropy crystals, DNA origami, etc. Bulk solids can transform to the disordered state using dc electric pulses, ultrafast heating/cooling, band-to-band absorption or mechanical stress, for example, using the AFM cantilever. The fundamental result of our study is an understanding of light-matter interactions in systems with "crystal-liquid" duality, in which the main role is played by inelastic broadband light scattering due to indirect optical transitions throughout the entire Brillouin zone rather than direct absorption of light using the electron states near the edges of the lowest bandgap," says Sergey Kharintsev, Professor of the Department of Optics and Nanophotonics.
"The same effect occurs at the edge of a perovskite crystal, which is an extended defect. The beauty of the developed physical model is that edge PL arises from broadband inelastic light scattering or electronic Raman scattering rather than an absorption-emission-absorption mechanism," says co-author Elina Battalova. "This is a widespread phenomenon in perovskite photonics when the light focuses on the crystal surface and its edge sparkles mesmerizingly. A paradox is that the glowing edge occurs under sub-band illumination, when the photon energy is insufficient to carry out optical transitions. This is the reason why twin domains are seen in perovskites exposed to non-resonant illumination, and disappear under band-to-band pumping."
"The ERS mechanism drives trapped electrons from shallow and mid-gap states due to the expanded momentum of optical near-field. Upon supplying the carriers to the conduction band, ERS leads to local heating and partial destruction of the crystal. This claim is manifested by both PL and Raman blinking. It is important to emphasize that these processes run during sub-band pumping, showing single-photon anti-Stokes photoluminescence shifted by 411 meV. Together with spontaneous amplified photoluminescence, we observed sporadically-tunable lasing at room temperature," continues Kharintsev.
The developed physical model, based on the interaction of near-field photons with trapped carriers, is critical in diverse fields of nonlocal photonics, optoelectronics and material science. These include enhanced photocatalysis for hydrogen energetics, atomic-sensitive sensors, tunable broadband solar cells, true white LEDs, resonatorless lasers, sub-diffraction wide-field visualization, chipless neuromorphic computing and high-temperature superconductivity.
More information:
Extreme Electron-Photon Interaction in Disordered Perovskites
onlinelibrary.wiley.com/doi/10.1002/advs.202405709
Provided by Kazan Federal University