Core-cladding-like phosphor ceramic wafer: A path to ultrahigh luminance

The utilization of blue lasers to excite phosphor materials holds great potential for the development of high-brightness laser-driven light sources. However, phosphor materials that can simultaneously constrain light spot expansion and enhance maximum luminous flux have been elusive, thereby limiting output luminance. Herein, optical fiber-inspired core-cladding phosphor ceramics (CCPC) of YAG:Ce@Al₂O₃ wafers were engineered using a gel-casting technique to restrict the light spot expansion. The smaller refractive index of Al₂O₃, combined with the dense and sharp core-cladding interface of these CCPC, effectively confines the light spot area. The sample with a 1.0 mm core diameter exhibits a small spot size nearly identical to that of the incident blue laser beam. Furthermore, the high thermal conductivity of the non-luminescent Al₂O₃ cladding endows the CCPC with an impressive luminance saturation threshold of 30 W·mm⁻² and a maximum luminous flux of 2100 lm for white light within a straightforward transmissive optical setup. The combination of a confined light spot area and an elevated luminous flux results in an ultra-high luminance of 3900 lm·mm⁻², surpassing current reports. This research presents a pioneering approach to the design of phosphor materials, targeting the realization of light sources with unprecedented luminance for broad frontier applications.