Luminescence, energy transfer and optical thermometry of a novel narrow red emitting phosphor: Cs₂WO₂F₄:Mn⁴

A novel red emitting Cs₂WO₂F₄:Mn⁴⁺ phosphor was successfully synthesized by a two-step wet chemical method. The crystal structure, morphology, and elemental composition were confirmed by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. The luminescence properties were investigated from emission, excitation and luminescence decay curves in the temperature region of 10-500 K. The application of non-contact optical thermometry of Cs₂WO₂F₄:Mn⁴⁺ based on the fluorescence intensity ratio (FIR) of the two coupled anti-Stokes and Stokes sidebands is discussed. The as-prepared Cs₂WO₂F₄:Mn⁴⁺ phosphor shows a bright narrow red emission at 632 nm under excitation by a blue lamp at 470 nm and it also presents a broad and yellow-white intrinsic tungstate emission (∼520 nm) under UV excitation. The mechanism of energy transfer from [WO₂F₄]^2- (the sensitizer) to Mn⁴⁺ (the activator) is discussed.