White light emitting diodes based on green graphene quantum dots and red graphene quantum dots

Abstract

White light emitting diodes (WLEDs) have attracted the attention of numerous scholars because of its high photoelectric conversion efficiency, low energy consumption and high reliability. They are known as the new generation of lighting energy in the twenty first century. Currently, the most common WLEDs are combined by blue LED chip and ce-doped yttrium aluminum garnet (YAG: Ce3+) yellow phosphors. The advantages are simple production, low cost and high luminous efficiency. However, WLEDs made of blue LED chip and yellow phosphors lacks red spectrum and exhibits luminescence, and its color rendering index (CRI) is low, usually only 70. At the same time, quantum dots (QDs) are considered to be the most potential materials for WLEDs color conversion layers due to their wide excitation spectrum, narrow emission spectrum, adjustable band gap and high quantum yield. In this paper, we fabricated green graphene QDs (GQDs) and red GQDs, measured and analyzed their morphology, structure and photoluminescence. The green GQDs, red GQDs and yellow phosphors were used to fabricate the WLEDs. The produced WLEDs showed excellent optical performance and working performance, among which Commission International de L 'Eclairage (CIE) chromaticity coordinates are (0.3332, 0.3359), and the correlated color temperature (CCT) is 5464 K (driving current is 30 mA). Electroluminescence (EL) spectra of the device at different currents were also measured.