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 (λmax ≈ 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. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim