Photo-induced degradation and thermal decomposition in ZnSnF6·6H2O:Mn4+ red-emitting phosphor

• ZnSnF6·6H2O:Mn4+ red phosphor was synthesized for the first time using a simple method.
• Structural and photoluminescent properties of this red phosphor was clarified.
• Photo-induced luminescence degradation was observed and analyzed in detail.
• Comprehensive discussion was given on the I2-IV-F6:Mn4+ and II-IV-F6:Mn4+ hexafluoride red phosphors.

ZnSnF6·6H2O:Mn4+ red-emitting hexahydrate phosphor is synthesized by the chemical reaction method, and its unique structural and optical properties are investigated using X-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation spectroscopy, and electron spin resonance (ESR) spectroscopy. The Mn4+-activated phosphor exhibits remarkable degradation in the PL intensity under Xe lamp exposure and also by the coherent laser beam irradiation with the following order of degradation: Ar+ (488 nm) > He–Cd (325 nm) > He–Ne laser (632.8 nm). The mechanism of degradation is considered to be due to a change in the valence state of manganese ions from Mn4+ to Mn5+ by the photooxidation and/or disproportionation. The ESR measurement supports decreased Mn4+ spin density in the Xe-lamp exposed, degraded sample. The changes in the structural and PL properties are also observed after thermal annealing above ∼100 °C and explained by the thermal-annealing-induced dehydration/decomposition of the host material.