K replaces Rb towards cyan to red ultra-wideband perovskite-type phosphors for full-spectrum lighting

Abstract

Near-ultraviolet-excited high-performance broad-emission phosphors are still an important challenge in full-spectrum LED lighting. According to the perovskite structure Rb2CaPO4F and K2CaPO4F, the broadband phosphor Rb2-wKwCaPO4F: Eu2+ (w = 0–2) suitable for near-ultraviolet excitation was studied, especially the phosphors with w of 0.5, 1 and 1.5. These three phosphors emit green, yellow and red light under excitation at 395 nm, and the full width at half maximum (FWHM) is 144 nm, 182 nm, and 174 nm, respectively, which is wider than the FWHM of commercial phosphors. Through the calculation of the formation energy and the change of the average bond length after Eu2+ doping, it can be determined that Eu2+ mainly occupies Ca2+ site. As K replaces Rb to change the coordination environment of Eu2+, the emission wavelength is continuously red-shifted and the FWHM is also changed. The series of phosphors Rb2-wKwCaPO4F: Eu2+ (w = 0–2) have high quantum efficiency and excellent thermal stability (more than 80%@150 °C of the integrated emission intensity at room temperature). The white LED synthesized by using the series of phosphors have a high color rendering index (Ra is greater than 90), a wide spectral range and a suitable correlated color temperature. These results indicate that Rb2-wKwCaPO4F: Eu2+ (w = 0–2) phosphors have great potential in full-spectrum LED lighting applications. This research also verifies that the photoluminescence adjustment strategy through cation substitution is the key to achieve tunable emission.