Tunable dual-mode emission with excellent thermal stability in Ca₄ZrGe₃O₁₂ : Eu phosphors prepared in air for NUV-LEDs

Abstract

Novel dual valence Eu-doped Ca₄ZrGe₃O₁₂ (CZGO) phosphors were successfully fabricated in air atmosphere through a solid-state route. Their crystal structure, photoluminescence properties as well as thermal quenching performance were investigated systematically. The spectra show that part of Eu³⁺ were reduced to Eu²⁺ and the mechanism is interpreted by the charge compensation. By altering Eu concentration, multi-color luminescence covering from blue to red is realized when irradiated by 370 nm light, which perfectly matches with the near ultraviolet (NUV) light-emitting diode (LED) chips. More importantly, under NUV excitation, luminescent intensities are almost unchanged even up to 423 K. And chromaticity exhibits only a tiny shift with growing temperature. Such suitable luminescent spectra and superior thermal stability indicate that CZGO:Eu phosphors are promising candidates for blue-red components in NUV pumped W-LEDs. Finally, the fabricated W-LED based on the combination of CZGO:Eu phosphors, Ba₂SiO₄:Eu²⁺ and a 365 nm NUV-LED chip gives a high color rendering index, a low correlated color temperature and suitable CIE chromaticity coordinates.