Bi-color phosphor-in-glass films achieve superior color quality laser-driven stage spotlights

Abstract

Laser-driven white lighting sources promise super-high brightness, good directionality and high efficiency, but are usually suffering from low color rendering index (Ra), high correlated color temperature (CCT) and poor light uniformity. To solve these problems, we designed bi-color phosphor-in-glass (PiG) films containing broadband green and red phosphors, and introduced Al2O3 particles as scattering centers into the PiG films. The addition of Al2O3 effectively increases the Ra value from 83 to 93, and greatly improves the angular uniformity in Ra and CCT with Cv(Ra) decreasing from 14.96% to 0.16% and Cv(CCT) decreasing from 45.87% to 1.5%. The coefficient of variation (Cv) is used to evaluate the light uniformity, and the smaller the value, the better the uniformity. The color temperatures can be tuned in a wide range of 2500 ∼ 6300 K by controlling the content of Al2O3 or the ratios of phosphor-to-glass in the films as well as their thicknesses, while high Ra values of > 90 are maintained. A prototype laser-driven white light with excellent color qualities (Ra = 95, Rf = 95, Rg = 104, R9 = 99, R15 = 98) and a high luminous efficacy of 102 lm/W was demonstrated for stage spotlights by optimizing the composition and structure of the bi-color PiG films. This work highlights the roles of secondary phase in heat dissipation and light scattering, and provides ideas to design PiG color converter films for use in super-high color quality laser lighting.