Design of luminescence in (Sr,Gd)Li(Al,Mg)3N4:Eu2+ deep red phosphors via crystal field engineering for full-spectrum WLEDs

Red phosphor, with longer wavelength, is highly desirable for full-spectrum WLEDs. Targeted deep red phosphors (Sr,Gd)Li(Al,Mg)3N4:Eu2+ were designed from the initial model of SrLiAl3N4:Eu2+ by structural modification. The correlations among structural evolution, crystal-field environment, and luminescence properties were elucidated. Replacing Sr2+ with Gd3+ in (Sr,Gd)LiAl3N4:Eu2+ leads to the enhanced crystal field splitting, larger Stokes shift, and increased structural polyhedron distortion differences, consequently resulting in spectral red-shift and broadening. For further spectral tuning, Mg, with lower electronegativity, was also introduced to modify the local crystal structure, consequently resulting in a further red-shift towards 675 nm and enhanced photoluminescence intensity in (Sr,Gd)Li(Al,Mg)3N4:Eu2+. What's more, w-LEDs were fabricated by using blue LED chip, blue, green, red and deep red ((Sr,Gd)Li(Al,Mg)3N4:Eu2+) phosphors whose color rendering index were Ra 96.0 and R9 97.7. All above results demonstrate that the partial replacements of Sr2+ by Gd3+ and Al3+ by Mg2+ are effective methods for spectral modulation and (Sr,Gd)Li(Al,Mg)3N4:Eu2+ phosphors are suitable for high-quality full-spectrum WLEDs.