A Thermally Robust La₃Si₆N₁₁:Ce‐in‐Glass Film for High‐Brightness Blue‐Laser‐Driven Solid State Lighting

Abstract

Color converter is a key luminescent material in the laser‐driven solid state lighting, which must bear high‐density excitation and serious thermal attack from the incident laser. Here, a thermally robust yellow‐emitting La3Si6N11:Ce‐in‐glass (LSN:Ce‐PiG) film for laser lighting is reported by co‐firing the LSN:Ce and glass powders on a thermally conductive sapphire substrate. No detectable interfacial reaction occurs between the LSN:Ce particle and glass matrix, enabling the film to fully inherit the original thermal robustness and high quantum efficiency. The optical performance of LSN:Ce‐PiG‐converted white laser light has been effectively optimized by changing the phosphor‐to‐glass (PtG) ratio and the film thickness. The highest light conversion efficiency is respectively achieved at PtG = 2:3 and the thickness of 70 µm, and the saturation threshold is found to decrease with either a higher PtG ratio or a thicker film. The optimized LSN:Ce‐PiG film (P2G3‐50) can withstand a maximum laser power density of 12.91 W mm−2 and produce a cool white light with a high luminous flux of 1076 lm (luminance of 773 Mcd m−2), a luminous efficiency of 166.05 lm W−1, a color rendering index of 70. These results make the LSN:Ce‐PiG film a considerably promising color converter for laser lighting.

Unique Design Strategy for Laser‐Driven Color Converters Enabling Superhigh‐Luminance and High‐Directionality White Light

“…Although the thickness varies widely, the color coordinates at the same excitation powers are close (see Figure d). This is significantly different from that observed in the transmission configuration mode where a slight change in thickness leads to a significant variation in color coordinates . In transmission mode, the CCT can change from ≈6000 to ≈7500 K when sample thickness varies only from 28 to 20 µm .…”

“…Obviously, blue LDs have inherent advantages of high optical flux density and low etendue, and are appreciated for small luminaire designs . At the same time, it brings new challenges to the design of color converters to accommodate the distinguishing features of LDs . Firstly, the phosphor materials must withstand long‐term high flux density laser irradiations and dissipate the generated heat within the small laser spot.…”

Development of sialon phosphors and their applications to solid-state lighting

“…The prototype of the laser-driven white light, with a high luminous flux of 1076 lm, a luminous efficiency of 166.05 lm/W and a CRI of 70, was demonstrated. 68)…”

High Efficiency Green‐Emitting LuAG:Ce Ceramic Phosphors for Laser Diode Lighting

“…[8][9][10][11] The order of magnitude higher power density of LD than that of LED launches a revolution in packaging technology for color converters. Remote type all-inorganic phosphors, including single-crystal phosphors (SCPs), [12,13] phosphors in glasses (PiGs), [14][15][16][17][18] and ceramic phosphors (CPs), [19][20][21][22][23] have been proposed to overcome the thermal degradation effect in LD lighting. CPs are currently proved to be an excellent type attributed to advantages of superior thermal conductivity (4-25 W m −1 K −1 ) and stronger thermal shock resistance.…”