Observation and Analysis of Luminescence of a Colloidal-Organized Suspension of Nanodiamond

This paper investigates the spectral properties of colloidally ordered systems formed from 100 nm nanodiamonds (NDs) synthesized using the high-pressure high-temperature (HPHT) method. Despite the polydispersity and irregular shape of the particles, aqueous ND suspensions can colloidally order via repeated centrifugation-induced sedimentation. To the best of our knowledge, this is the first spectroscopic study of such ordered ND systems. In our study, we obtained colloidally ordered ND structures, evidenced by the formation of rainbow-colored layers in the centrifuge tubes. Fragments extracted from these layers were subjected to microscopic and spectroscopic characterization. Spectroscopic measurements with 488 nm wavelength laser reveal modulated emission in a narrower spectral range, lying within the characteristic broad emission band of NDs and indicating the formation of ordered structures with a characteristic micrometer scale. In view of the intrinsic luminescence of NDs, we propose that these structures are best regarded as analogous to colloidal photonic crystals with intrinsic luminescence. This concept can significantly extend the functionality of ND-based materials and offers new opportunities for fundamental optical studies and practical photonic applications.