Mixed Cation and Anion Perovskite Nanocrystals for Amplified Spontaneous Emission

Perovskite nanocrystals (PeNCs), which have the form ABX₃, exhibit many interesting optical properties, including broadband UV absorption and high color purity in luminescense. In this work, we chose the B site to be fixed as lead, due to its performance advantages¹. The choice of A-site (cationic) and X-site (anionic) occupants is variable, and has a marked effect on the PeNC spectrum. Depending on the species in these sites, it can be difficult to synthesize highly concentrated PeNCs. Concentration is vitally important for the application of PeNCs as a lasing medium. However, by utilizing the principles of A-site and halogen exchange, we can optimize the synthesis process for only certain varieties of PeNCs, thereby removing a barrier for the use of all varieties of PeNCs in lasers. Halogen exchange and A-site exchange methods of perovskite nanocrystal (PeNC) synthesis show promise for the use of PeNCs as precisely tunable laser sources—a key advantage in closing the laser “green gap”. In this work, we show that these methods can be used in tandem to fine-tune amplified spontaneous emission peak wavelengths by mixing pre-synthesized samples in desired ratios, thereby producing composite nanocrystal solutions that exhibit a single, strong emission peak—despite their component solutions having distinct crystal morphologies, and therefore distinct emission peaks. PeNCs were synthesized using ligand-assisted reprecipitation and subsequently dispersed in toluene and cyclohexane, where PL, absorption, and XRD measurements were taken for PeNCs in solution and as thin films on quartz glass substrates.

¹Zhang et al., The importance of elemental lead to perovskites photovoltaics, Chemistry of Inorganic Materials, Volume 1, 2023