Closing the Deep-Blue Gap: Realizing Narrow-Band Deep-Blue Emission with Strong n-UV Excitation by Cationic Substitution for Full-Spectrum Warm W-LED Lighting

Since the strong blue light from the conventional blue chip has negative effects on human health, near-ultraviolet (n-UV) white light-emitting diodes (W-LEDs) have been widely studied. However, the photoluminescence spectrum generated by tricolor (blue, green, and red) phosphors contains a notable cavity in the deep-blue region (400–430 nm), which reduces the color quality. In this work, we report a novel series of narrow-band deep-blue-emitting phosphors with strong n-UV excitation, Ln2Si2O7:Bi3+ (Ln = Gd, Y, Lu, Sc), and realize the tuning of emission from 422 to 403 nm via cationic substitution, which bridges the deep-blue gap. All of these phosphors are effectively excited by n-UV radiation at approximately 370 nm and exhibit narrow-band deep-blue emission with a full width at half-maximum (FWHM) < 50 nm. Among them, Sc2Si2O7:Bi3+ generates 403 nm deep-blue emission with a 38 nm FWHM under 372 nm n-UV excitation, with high luminescence intensity and excellent thermal stability. Finally, 365 nm n-UV-pumped phosphor-converted (pc) W-LED devices are fabricated by combining Sc2Si2O7:Bi3+ and commercially available phosphors, and they have a high color-rendering index (Ra) of 95.4 and a low correlated color temperature (CCT) of 3736 K. This result suggests that these phosphors have potential applications in full-spectrum warm white lighting.