Generating Cyan Emission via Ammonia-Thermal Nitridation: Na18−xCa13+xMg5(PO4−yNy)18:Eu2+

Abstract

As phosphor-converted LEDs continue to displace traditional light technologies, developing new down-conversion materials remains essential for improving color quality and efficiency. This research introduces a cyan-emitting oxynitride phosphor, Na_13.57Ca_17.43Mg₅(PO_3.75N_0.25)₁₈:Eu²⁺, synthesized through ammonolysis of the oxide, Na₁₈Ca₁₃Mg₅(PO₄)₁₈. The presence of nitrogen was validated using a suite of advanced analytical techniques, including Rietveld co-refinement of synchrotron X-ray and neutron diffraction data, X-ray photoelectron spectroscopy, thermogravimetric analysis, and diffuse reflectance spectroscopy. This oxynitride phosphor was subsequently shown to exhibit a broad excitation spectrum covering the UV (>350 nm) to the violet (425 nm) portions of the electromagnetic spectrum, down-converting the absorbed light, generating an efficient cyan emission. A prototype light using the new Eu2+-substituted oxynitride produced a functional (daylight) white light when paired with a violet LED and commercial blue and red-emitting phosphor. This research not only introduces a promising phosphor for LED applications but also highlights a practical approach to obtain novel oxynitrides from disordered oxides with a cost-efficient synthesis method, potentially paving the way for advancements in phosphor-based lighting technologies.