Droplet Microfluidic Synthesis of Halide Perovskites Affords Upconversion Lasing in Mie-Resonant Cuboids

Halide perovskite structures of submicrometer sizes have become outstanding tools for various applications in photonics. However, despite the high potential of perovskites, their stable, scalable, and reproducible synthesis with a fine control over the size of the resulting structures (a narrow size distribution) is still challenging. In this work, we report on the synthesis of all-inorganic lead halide perovskites via droplet microfluidics, where a formed droplet acts as a sealed microreactor for perovskites' nucleation and growth. For synthesis, we use two systems with different carrier fluids (either fluorinated oil or distilled water). The developed microfluidic system enables the fabrication of perovskite particles with sizes ranging from nanometers to submicrometers with a narrow size distribution, which depends on temperature and hydrophilic-lipophilic balance. Using the advantages of this synthesis method, we obtain optically resonant submicrometer cuboid particles. We study their lasing properties upon two-photon nonlinear excitation on a metallic substrate and reveal a significant reduction of the lasing threshold down to around 230 μJ/cm2 when the pump wavelength λ corresponds to the first-order Mie resonance of the particle (at λ = 950 nm for the particle dimensions 440 × 640 × 710 nm3). Our results can be useful for the development of infrared laser beam visualizers and nonlinear imaging.