Mn⁴⁺ activated Al₂O₃ red-emitting ceramic phosphor with excellent thermal conductivity

An Al₂O₃:Mn⁴⁺, Mg²⁺ red emitting ceramic phosphor, which can be effectively excited by ultraviolet and blue light, was successfully synthesized via solid-state reaction in an oxygen and air atmosphere. The ceramic sintered in oxygen atmosphere has higher optical transmittance and stronger luminescence intensity than the ceramic sintered in the air, which is more suitable for LED application. Since the structure of α-Al₂O₃ is very simple, it is convenient to study the factors affecting the Mn⁴⁺ luminescence. The crystal-strength parameter Dq, Racah parameters B and C, and the nephelauxetic ratio β₁ were calculated to investigate the influence of crystal field strength and nephelauxetic effect on the emission of Mn⁴⁺ in the Al₂O₃ host. The ratio of Dq to B was 1.74, which was lower than 2.2. This indicated that the Mn⁴⁺ ions in the α-Al₂O₃ host were in a weak crystal field environment. Under the 395 nm and 460 nm excitations, quantum yields (QY) of the sample were measured to be 46% and 28.7%, respectively. The density measured by the Archimedes method was 3.61 g/cm³. The ceramic also showed an excellent thermal conductivity value, which was as high as 26.27 W·m^-1·K^-1@30 °C.