Energy transfer and thermal stability enhancement in Ce/Cr co-doped Al₂O₃/YAG eutectic phosphor ceramics for broadband red-emission

The Ce/Cr co-doped Al₂O₃/YAG eutectic phosphor ceramics for WLEDs with functional and structural integration were successfully solidified by laser floating zone melting (LFZM) method (>10⁴ K/cm). The influences of Cr³⁺ doping on microstructure, mechanical properties and optical characteristics of the eutectic phosphor ceramics were systematically and efficiently investigated. The results showed that the eutectic phosphor ceramics presented typical “Chinese script” (CS) irregular eutectic structure, consisting of interpenetrated Al₂O₃:Cr³⁺ and YAG:Ce³⁺/Cr³⁺ phases. Under the excitation of the blue light (460 nm), the eutectic phosphor ceramics exhibited excellent red-light emission with wavelengths of about 687 nm, 693 nm and 707 nm. The emission intensity could be still maintained at a high level of 68% at 127 °C compared to the intensity at room temperature, referring to good thermal stability of the eutectic phosphor ceramics. Especially, the color rendering index (Ra = 80) and the correlative color temperature (Tc = 5606 K) of the present eutectic phosphor were simultaneously improved by the energy transfer between Ce³⁺ and Cr³⁺ ions. The present Ce/Cr co-doped Al₂O₃/YAG eutectic phosphor ceramics can be used as excellent candidates for high performance warm WLEDs.