Microsized Red Luminescent MgAl₂O₄:Mn⁴⁺ Single-Crystal Phosphor Grown in Molten Salt for White LEDs

A single-crystalline defect-less phosphor is desired for efficient luminescence of the therein doped optical activators. In this paper, microsized MgAl₂O₄:Mn⁴⁺ single-crystal phosphors with bright red luminescence were grown in molten LiCl salt at 950 °C, for application in blue LED pumped white lighting. By comparing the phosphor formation from various Mg²⁺- and Al³⁺-bearing sources, both the template-formation and the dissolution-diffusion processes were evidenced to account for the formation of the microsized MgAl₂O₄:Mn⁴⁺ crystallites. Using nano γ-Al₂O₃ as the Al³⁺-bearing precursor, the uniform MgAl₂O₄:Mn⁴⁺ microcrystallites with a {111} planes-exposed tetragonal bipyramid morphology were obtained. The photoluminescence property was studied at various temperatures, and Mg ↔ Al anti-site disorder induced luminescence broadening was discussed. The Mn^{4+ 2}E_g → ⁴A_2g transition in MgAl₂O₄ shows a quite short luminescence wavelength peaking at 651 nm and ultrabroadband emission extending to 850 nm. The luminescence is relatively robust against thermal effect with relatively high thermal quenching temperature of 400 K and activation energy of 0.23 eV. Employing the red-emitting MgAl₂O₄:Mn⁴⁺ crystallites, blue LED pumped white lighting prototypes were fabricated which simulate the solar-like spectrum and show neutral to warm white.