Improving the photostability and water resistance stability of chalcogenide red phosphor with inert CaF2 shells

(Ca,Sr)S:Eu2+ as an important commercial red phosphor has been widely used in our daily life. However, (Ca,Sr)S:Eu2+ is extremely sensitive to moisture and ultraviolet (UV) light, which severely limits its service life and wide applications. Here epitaxial growth of dense CaF2 shell on the surface of (Ca,Sr)S:Eu2+ particles is successfully achieved by a liquid-phase thermal decomposition method. The red emission of the (Ca,Sr)S:Eu2+ phosphor is increased as much as 40% after coating with a CaF2 shell. This is attributed to the effective protection of luminescent center of Eu2+ ions in the core from surface quenching. Moreover, after continuous exposure to intense sunlight in air for 9 days, no luminescence degradation is observed for the (Ca,Sr)S:Eu2+@CaF2 sample, while the red emission of the (Ca,Sr)S:Eu2+ phosphor is severely quenched by 66%. The water resistance experiments show that the dense shell of CaF2 can protect the crystal structure of (Ca,Sr)S by suppressing the hydrolysis reaction. The red emission of the (Ca,Sr)S:Eu2+@CaF2 sample after being fully soaked in water for 30 min is comparable to that of the original (Ca,Sr)S:Eu2+ phosphors. Our results provide a new and versatile avenue to improve the stabilities of chalcogenide phosphors, thus making them attractive for wide applications. An inert CaF2 layer is successfully coated on the surface of (Ca,Sr)S:Eu2+ particles by a liquid-phase thermal decomposition method. This stable shell effectively protects the inner chalcogenide phosphors against UV irradiation, moisture and atmosphere, thus enabling their wide applications. [Display omitted] •An inert CaF2 shell successfully coated on the surface of chalcogenide phosphors.•The epitaxial CaF2 shell protects the luminescent center of Eu2+ ions in the core.•The CaF2 shell protects (Ca,Sr)S against UV irradiation, atmosphere and water.•Development of a novel strategy to improve stabilities of chalcogenide phosphors.