A novel inequivalent double-site substituted red phosphor Li4AlSbO6:Mn4+ with high color purity: its structure, photoluminescence properties, and application in warm white LEDs

Abstract

Non-rare-earth Mn⁴⁺-doped oxide red phosphors have received increasing attention in the field of white light-emitting diodes (LEDs) for their admirable chemical stability and spectral properties. Here, a new inequivalent double-site substituted Mn⁴⁺-doped Li₄AlSbO₆ (LAS:Mn⁴⁺) phosphor with deep-red emission was successfully synthesized via the conventional solid-state reaction method. X-ray powder diffraction (XRD) and Rietveld refinement analysis confirm that LAS is isostructural with Li₄MnSbO₆, belonging to the monoclinic system with a space group of C2/c. The LAS:Mn⁴⁺ phosphor has two inequivalent Mn⁴⁺ luminescence centers situated at the Al³⁺ and Sb⁵⁺ sites, respectively, and two intense and broad excitation bands in the near-ultraviolet (n-UV, ∼397 nm) and blue (∼467 nm) regions, indicating that it is very suitable for being excited with commercial n-UV and blue LED chips. Under 467 nm excitation, the phosphor emits bright red light centered at 673 nm with a high color purity of over 99%, originated from the ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. The optimal content of Mn⁴⁺ in LAS is 0.5 mol% and its corresponding quantum yield is nearly 40%. Furthermore, it also has good thermal stability with an activation energy of 0.52 eV. A white LED device fabricated with the as-prepared LAS:Mn⁴⁺ phosphor exhibits a low correlated color temperature (CCT = 3534 K) and a high color rendering index (CRI = 81.4), implying that LAS:Mn⁴⁺ is a promising red phosphor for warm white LEDs.