2D Arrangement of Polymer Microsphere Photonic Cavities Doped with Novel N‐Rich Carbon Quantum Dots Display Enhanced One‐ and Two‐Photon Luminescence Driven by Optical Resonances

Abstract Luminescent carbon dots (CDs) are emerging as a potential eco‐friendly alternative to standard metal‐based semiconductor quantum dots. A solvatothermal method to prepare crystalline, nitrogen‐rich, surface‐passivated, and rare excitation wavelength‐independent green‐emitting (λ_max ≈ 522 nm in solution and 536 nm in solid) CDs from a pyridine diamine precursor in ethanol solvent is reported here. In comparison to a neat thin film of CDs, a film of CD‐doped polystyrene microspheres (PS‐CDs) displays a remarkable enhancement of the photoluminescence emission intensity driven by optical cavity effect of the composite microspheres. Apart from downconversion one‐photon luminescence, upon excitation with 800 nm femtosecond pulse laser, pure CDs and PS‐CDs exhibit enhanced upconversion two‐photon luminescence in the range of about 410–580 nm.