(Ca0.8Mg0.2Cl2/SiO2):Eu2+: a violet-blue emitting phosphor with a low UV content for UV-LED based phototherapy illuminators

Abstract

(Ca_1−x−yMg_xSr_yCl₂/SiO₂):Eu²⁺ phosphors with intense violet-blue emission were synthesized through a high temperature solid-state reaction method. The colour of the emission is tunable from violet-blue to blue as well as to the violet spectral region by adjusting the concentration of Mg²⁺ or Sr²⁺, respectively. An abnormal shift in emission wavelength with the ratio of alkaline earth metal ions was observed and explained by combining electronegativity with the crystal field splitting equation. The UV light content in the emission spectra of (Ca_0.8Mg_0.2Cl₂/SiO₂):0.003Eu²⁺ was successfully reduced below 0.1%, thus providing a safer violet-blue light source for phototherapy. Moreover, the measurement results showed an emission band peaked at 440 nm with a full-width at half maximum of 40 nm under 343 nm excitation, which matches with the most effective range for the treatment of hyperbilirubinemia. CIE chromaticity coordinates of (0.156, 0.044) and an internal quantum efficiency of 41.7% were obtained. The temperature-dependent photoluminescence spectra of (Ca_0.8Mg_0.2Cl₂/SiO₂):0.003Eu²⁺ were also presented. These excellent properties reveal that the violet-blue emitting phosphor could be a potential candidate in converting near-UV radiation to violet-blue emission for phototherapy when combined with UV LED chips.