Silicon microspheres with a diameter in the range of 2–3 micrometers constitute photonic nanocavities that emit light through their Mie resonances when heated at high temperatures. At 500–600 °C these microresonators show a particular mid-infrared (MIR) emission dominated by the lowest order modes. Such resonances feature a large free spectral range, about 600 cm−1, and a high proximity to the critical coupling condition. In fact, resonances with high-quality factor, around 160 are found. It corresponds to the limit of detection of their measuring setup, being 600 the theoretical value. Most importantly, several modes emit light above the calculated black body limit because they feature an optical absorption cross-section larger than their geometric one. All these characteristics set silicon microspheres as very promising zero-dimensional materials for developing micrometric and sub-wavelength light sources in the MIR.
Supporting information with additional figures and explanations.
A precise knowledge of the optical properties, specifically the refractive index, of organic/inorganic perovskites, is essential for pushing forward the performance of the current photovoltaic devices that are being developed from these materials. Here we show a robust method for determining the real and the imaginary part of the refractive index of MAPbBr3 thin films and micrometer size single crystals with planar geometry. The simultaneous fit of both the optical transmittance and the photoluminescence spectra to theoretical models defines unambiguously the refractive index and the crystal thickness. Because the method relies on the optical resonance phenomenon occurring in these microstructures, it can be used to further develop optical microcavities from perovskites or from other optical materials.
Planck’s law constitutes one of the cornerstones in physics. It explains the well-known spectrum of an ideal blackbody consisting of a smooth curve, whose peak wavelength and intensity depend on the temperature of the body. This scenario changes drastically, however,
when the size of the emitting object is comparable to the wavelength of the emitted radiation. Here we show that a silicon microsphere (2−3 μm in diameter) heated to around 800 °C yields a thermal emission spectrum consisting of pronounced peaks that are associated with Mie resonances. We experimentally demonstrate in the near-infrared the existence of modes with an ultrahigh quality factor, Q, of 400, which is substantially higher than values reported so far, and set a new benchmark in the field of thermal emission. Simulations predict that the thermal response of the microspheres is very fast, about 15 μs. Additionally, the possibility of achieving light emission above the Planck limit at some frequency ranges is envisaged.