Unique light-induced degradation in yellow-emitting K2SiF6:Mn2+ phosphor

Photo-induced luminescence intensity degradation in yellow-emitting K2SiF6:Mn2+ phosphor is studied using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, PL decay analysis, and electron spin resonance (ESR) measurement. The yellow-emitting K2SiF6:Mn2+ phosphor exhibits remarkable degradation in the PL intensity under Xe lamp exposure. Coherent laser irradiation also induces degradation and its degree is in the order of He–Cd (λ = 325 nm) > Ar+ (488 nm) > He–Ne laser (632.8 nm). The degradation mechanism is proposed to be due to change in the valence state of manganese ions from Mn2+ to Mn3+ by the photooxidation (Mn2+ → Mn3+) or disproportionation reaction (2Mn2+ → Mn+ + Mn3+). The ESR measurement confirms the decreased Mn2+ spin density in the sample exposed with Xe lamp. The PLE spectrum suggests that the excitation of Mn3+ ions occurs through energy transfer upon absorption of exciting radiation by the Mn2+ ions. Thermal annealing of the degraded samples at ≥200 °C causes a blueshift in the PL emission band with an appearance of the Mn4+-related sharp red emission lines.