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 the maximum luminous flux have been elusive, thereby limiting the output luminance. In this study, optical fiber-inspired core–cladding phosphor ceramics (CCPC) of YAG:Ce@Al₂O₃ wafers were engineered using a gel–casting technique to restrict 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 has 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 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.