Realizing white LEDs with high luminous efficiency and high color rendering index by using double green phosphors

Abstract

The luminous efficiency of radiation (LER) and color rendering index (CRIs) are two key technological parameters of white light-emitting diodes (WLEDs), But there is always a trade-off between them, especially between LER and R9 (the 9th CRI of red color). Therefore, it is necessary to solve this problem by selecting suitable phosphors, mixing and coating it on the LED chip. In this work, two green phosphors and one red phosphor with less resorption of the two phosphors were selected by measuring the excitation spectra of seven red phosphors and emission spectra of two green phosphors. Then, different mass ratios of the phosphors were mixed with the AB glue and coated on the blue LED chips. After optimizing the ratio by measuring the luminescence spectra of the LED chips coated with different mass ratios of phosphors, high-quality white LEDs with LER = 142.74 lm/w, Ra = 97, R9 = 98.53, and the correlated color temperature of 3666 K were obtained. These LEDs have both high LER and high CRIs, further reducing the trade-off between luminous efficiency and color rendering index, which makes it can widely used for high quality solid state lighting. Keywords: Light-emitting diode, Phosphor, Luminous efficiency of radiation, Color rendering index