Improving the Angular Color Uniformity of Hybrid Phosphor Structures in White Light-Emitting Diodes

This letter examines a hybrid phosphor structure for white light-emitting diodes. The hybrid phosphor structure produces more efficient luminosity and more uniform angular correlated color temperature (CCT) than the conventional dispensing method. The experimental results show that the CCT deviation improved from 453 to 280 K between -70° and 70 °. This was likely caused by the large blue light divergent angle. The lumen output produced was higher than that produced by dispense and conformal phosphor structures. Therefore, the results show that the hybrid phosphor structure can be used in solid-state lighting.

I. Introduction

White light-emitting diodes (LEDs) have been developed and improved to the extent that they may replace traditional light sources, such as mercury lights and halogen lamps, in solid-state lighting (SSL) [1]. Usually, blue chip and yellow phosphor are combined to produce white-light LEDs for SSL [2]. To increase the adoption of LEDs, high-power white LEDs have been developed to enhance quantum or lumen efficiency [3]. Researches have shown that large electron-hole wavefunction overlap quantum wells and the surface plasmon approach increase internal quantum efficiency [4], [5]. Enhanced light extraction by internal reflection (ELiXIR) has been proposed to increase extraction efficiency. ELiXIR uses internal reflection to extract light from reflectors and enhance light extraction [6]. Luo et al. [7] used a hemisphere-shaped encapsulation to increase luminous efficiency and reduce the total internal reflection losses.