White light emitting diodes with a high colour rendering index of 98.3 using blue emissive carbon dots

Abstract

Fluorescent carbon dots (CDs) have become important materials for white light emitting diodes (WLEDs) due to their high stability, low cost and environmentally friendly nature. Here, blue carbon dots (B-CDs) were successfully prepared by a one-step hydrothermal method using theophylline and NaOH as raw materials. B-CDs were compounded with polyacrylamide (PAM), starch and chitosan (CTS) to make bright B-CD-based phosphors, respectively. Three different matrixes of B-CD-based phosphors were used to prepare WLEDs under UV chip excitation. The results show that the WLED prepared with the B-CDs/PAM phosphor exhibits the best performance. Compared to B-CDs, the fluorescence emission of the B-CDs/PAM phosphor is significantly enhanced and the quantum yield increases from 5.06% to 78.50% due to the inhibition of the non-radiative leap process by the matrix. The prepared WLED exhibits white light with colour coordinates of (0.3338, 0.3466), a correlated colour temperature (CCT) of 5442 K and a colour rendering index (CRI) of 98.3. Such a high CRI fully reflects the true colour of the object and has great potential for indoor lighting devices to protect the human eye and relieve eye strain.