The lack of efficient red phosphors for near-ultraviolet (n-UV) chip-based white light-emitting diodes (WLEDs) remains a major challenge. In this work, we aim to boost the red emission of Eu³⁺-activated CaLaGaO₄ (CLGO) phosphors via Na⁺ doping and to evaluate their potential for WLED applications.
A series of Na⁺-doped Ca_1-0.5xLa_0.7Eu_0.3GaO₄:xNa⁺ (CLEGO: xNa⁺, x = 0-1.7%) red phosphors were synthesized by a conventional high-temperature solid-state reaction at 1246 ℃. The crystal structure and phase purity were characterized by X-ray diffraction (XRD) and Rietveld refinement. Morphology and elemental distribution were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Photoluminescence (PL) excitation and emission spectra, temperature-dependent PL (298-498 K), fluorescence decay curves, and absolute quantum yields (QY) were measured. Finally, a WLED device was fabricated by combining the optimized red phosphor with commercial BaMgAl₁₀O₁₇:Eu²⁺ (blue) and Sr₂SiO₄:Eu²⁺ (green) phosphors on a 392 nm n-UV chip.
XRD confirms that all samples are phase-pure with an olivine-type structure. Rietveld refinement shows that Na⁺ substitutes Ca²⁺ sites, causing lattice expansion; the cell volume increases from 423.93 ų to 425.58 ų. Under 392 nm excitation, the ⁵D₀→⁷F₂ red emission at 609 nm is strongly enhanced by Na⁺ doping. The optimal intensity is achieved at x = 0.9%, being 1.82 times that of the undoped sample. The improvement is attributed to Na⁺-induced local lattice distortion, which reduces the symmetry around Eu³⁺ and increases the electric dipole transition probability.The CLEGO:0.9%Na⁺ phosphor exhibits a QY of 14.3%, which is 1.26 times that of the undoped sample. Temperature-dependent PL spectra reveal good thermal stability; at 498 K the emission intensity remains 64.9% of that at room temperature.The WLED device shows white light with chromaticity coordinates of (0.301, 0.354), a color rendering index (CRI) of 81.8, and a correlated color temperature (CCT) of 6900 K.
In summary, Na⁺ doping is an effective strategy to achieve significant luminescence enhancement in CLEGO:Eu³⁺ red-emitting phosphors. The optimized CLEGO:0.9%Na⁺ phosphor combines high emission intensity, acceptable quantum efficiency, good thermal stability, and suitable color coordinates. The fabricated WLED device demonstrates satisfactory white-light performance, indicating that this red phosphor is a promising candidate for n-UV chip-based WLED applications.