Realization of solid-state red fluorescence and concentration-induced multicolor emission from N,B co-doped carbon dots

As a new type of luminescent material,carbon dots(CDs)have attracted increased attention for their superior optical properties in recent years.However,solidstate fluorescent CDs,especially with red emission,are still a major challenge.Here,CDs with solid-state red emission were synthesized by co-doping of N and B using the one-step microwave method.The CD powder exhibits excitation-independent solid-state red fluorescence without any dispersion matrices,with optimum solid-state fluorescence wavelength of 623 nm.The hydrogen bonding interaction in CDs is helpful for solid-state fluorescence of CDs.The IG/ID value of CDs reaches up to 3.49,suggesting their very high graphitization degree,which is responsible for their red emission.In addition,CDs show the concentration-induced multicolor emission,which is attributed to the decreased energy gap in the high concentrated CD solution.To exploit their concentration-dependent emission,CDs with changing ratio in matrices are applied as a color-converting layer on ultraviolet chip to fabricate multicolor light-emitting diodes with light coordinates of(0.33,0.38),(0.41,0.48),(0.49,0.44),and(0.67,0.33),which belong to green,yellow,orange,and red light,respectively.