Ultrabroad-band, white light emission from carbon dot-based materials with hybrid fluorescence/phosphorescence for single component white light-emitting diodes

Abstract

Benefiting from the large Stokes shift between fluorescence and phosphorescence, fluorescence/phosphorescence dual-emitting carbon dots (CDs) have gradually entered at the stage of single-phase white light-emitting diodes (WLEDs) as ‘green material’. However, most of the developed dual-emitting CDs have weak phosphorescence, short emission wavelength and narrow emission band, resulting in relatively bluish white light emission and low color rendering index (CRI). Herein, an ultrabroad-band fluorescence/phosphorescence dual-emitting CD-based material (UB-CD@BA) is prepared by thermal treatment of boric acid (BA) and CDs with large conjugated structure. The stable covalent bonding between CDs and BA, as well as three-dimensional spatial restriction effect of self-polymerization BA molecules around CDs during long-term heating efficiently rigidified the single/triplet excited states of CDs from non-radiative deactivation, thus producing strong dual emissive materials with the high phosphorescence quantum yield of 21%. Remarkable, the prepared UB-CD@BA powders exhibit bright pure white light emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.32, 0.33) and the highest reported full width at half maximum of 250 nm. Based on the unique characteristics of UB-CD@BA, it was used as a color conversion layer to prepare a WLED with CIE coordinates of (0.35, 0.33) and the CRI value of 87.