A novel red phosphor of BaGe(1−x)TixF6:Mn4+ solid solution: facile hydrothermal controlled synthesis, microstructures and luminescent properties

Abstract

A series of BaGe_(1−x)Ti_xF₆:Mn⁴⁺ solid solution phosphor crystals have been successfully synthesized by a facile hydrothermal method. The crystal structure, morphology and size of the obtained samples were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The influences of Ti⁴⁺ doping concentration on the microstructures and photoluminescent (PL) properties of the as-synthesized crystals were also investigated comprehensively. The XRD results indicate that all the as-synthesized BaGe_(1−x)Ti_xF₆:Mn⁴⁺ samples are single phase solid solution crystals, although the doping concentration of Ti⁴⁺ has a remarkable influence on the lattice parameters. The SEM results reveal that all the as-synthesized BaGe_(1−x)Ti_xF₆:Mn⁴⁺ phosphor samples are microcrystals with a predominant rod-like morphology and lengths ranging from 1 to 8 μm and widths ranging from 0.2 to 2.5 μm. The PL spectra reveal that all the obtained crystals exhibit characteristic emission peaks of Mn⁴⁺ ion, and the intensity of the strongest red emission peak located at 636 nm distinctly fluctuated with x, showing the highest at x = 0.6. Under excitation of 467 nm blue light, all the obtained BaGe_(1−x)Ti_xF₆:Mn⁴⁺ samples can emit a warm red color, with a correlated color temperature (CCT) of less than 4500 K. The temperature-dependent PL emission spectra show that the BaGe_0.4Ti_0.6F₆:Mn⁴⁺ sample possesses outstanding thermal stability, which can retain 62.27% of its initial emission intensity (323 K) even at 423 K. Employing the synthesized BaGe_0.4Ti_0.6F₆:Mn⁴⁺ sample as a red component, a high-performance WLED with a correlated color temperature (CCT) of 4343 K, a color rendering index (CRI) of 93.2 and a luminous efficiency of 100.2 lm W⁻¹ was obtained. Our findings suggest that BaGe_(1−x)Ti_xF₆:Mn⁴⁺ can be a promising candidate as the red phosphor used in warm WLEDs.