Effect of optical bandgap variation induced by morphology difference on the luminescence properties of narrow-band green SrMgAl10O17:Mn2+ phosphors

Mn²⁺-activated narrow-band green phosphors are promising candidates for wide-gamut displays, yet their practical application in LED backlighting is often hindered by the intrinsic spin-forbidden nature of Mn²⁺ d-d transitions, which limits luminescence efficiency. In this work, we demonstrate that the morphology of SrMgAl₁₀O₁₇:Mn²⁺ (SMAO:Mn²⁺) phosphors plays a critical role in modulating their optical bandgap and luminescence properties. The phosphor exhibits strong blue-light-excited green emission peaking at 515 nm with a narrow full width at half maximum (FWHM) of 25-29 nm. By employing AlF₃ as a flux in synthesis, the resulting sample (AF-SMAO:Mn²⁺) shows well-crystallized, near-spherical hexagonal blocks, which contribute to a larger optical bandgap and reduced surface defects compared to the H₃BO₃-fluxed sample. High-resolution XPS spectra of O 1 s analysis reveals AF-SMAO:Mn²⁺ possesses a higher lattice-to-defect oxygen ratio (5.14:1) versus the H₃BO₃-fluxed sample (3.96:1), confirming reduced surface defects. These characteristics suppress nonradiative recombination, leading to a higher photoluminescence quantum yield (internal/external quantum efficiencies = 86.56%/31.19%) and a shorter decay time. Furthermore, the phosphor displays excellent thermal stability, maintaining over 80% of its initial emission intensity at 423 K after five thermal cycles, with the FWHM broadening only to 31 nm. A prototype white LED fabricated with the green SMAO:Mn²⁺ and red K₂SiF₆:Mn²⁺ on a 450 nm blue chip achieves a color gamut of 114% NTSC. These findings not only underscore the potential of SMAO:Mn²⁺ for advanced backlight displays but also provide a generalizable strategy for enhancing the performance of Mn²⁺-based phosphors through morphology and bandgap engineering.