Enhanced Color Quality of Phosphor-Converted White Laser Diodes Through Bicolor Phosphor-in-Glass

In this work, phosphor-converted white laser diodes (pc-WLDs) with high color quality were fabricated by combining blue lasers and bicolor phosphor-in-glass (PiG) converters. The bicolor PiGs were prepared by printing and sintering green/red phosphor glass films on sapphire substrates, and then applied in the transmission type of pc-WLDs. The PiG-based white laser diodes (WLDs) display broadband emission and their optical performances were adjusted by varying the PiG film thickness. When the film thickness increases from 80 to $160~\mu \text{m}$ , the luminous flux and correlated color temperature (CCT) of PiG-based WLDs are gradually decreased, and they still have high color rendering index (CRI). At the film thickness of $160~\mu \text{m}$ , the PiG-based WLD achieves high color quality with a CRI of ${R}_{a} = {88}$ , ${R}_{{9}} = {91}$ , and ${R}_{{13}} = {93}$ , a CCT of 4571 K, and a chromaticity coordinate of (0.3525, 0.3541) at a laser power of 2.4 W. Furthermore, the PiG-based WLD has stable color quality at high laser power and the luminous flux reaches to 553 lm at a laser power of 5 W. The results indicate that the bicolor PiG-based WLDs realize high-quality white light, which can promote the practical applications of laser lighting in high-quality fields.

I. Introduction

Solid-state lighting (SSL) source has been widely applied in our daily life due to its high light efficiency, long lifetime, and compact size [1]–[3]. With the increasing demand of high-brightness lighting, the SSL devices with high input current and power density have been developed, such as multichip integrated light-emitting diodes (LEDs) [4]–[6]. Unfortunately, the LEDs have an inevitable problem of efficiency droop under high power density, which limits their application in high-brightness lighting [7], [8]. On the contrary, laser diodes (LDs) are treated as new generation of high-brightness devices owing to their advantages of ultrahigh power, ultrahigh brightness, directional light emission, and long irradiation distance [9]–[11]. Importantly, the LDs display no efficiency droop even at an input power density of 25 kWcm⁻². These advantages promote the applications of LD device in automotive headlights, projection display, medical treatment, and visible light communication [12], [13].