Investigation on Anomalous Thermal Quenching of Mn4+ Luminescence in A2XF6:Mn4+

Studying luminescence properties of phosphor materials is not only of scientific interest, but also technological importance. Here, we investigate luminescence intensity as a function of temperature for Mn4+-activated fluoride and oxide phosphors. A recent study suggested that an anomalous increase in Mn4+ luminescence intensity (I (PL)) with increasing lattice temperature (T) in various fluoride phosphors is likely a pitfall caused by a diminishment in the optical path lengths of the spectrofluorometer stemming from lattice thermal expansion. We show that such anomalous enhancement of I (PL) is due to the increased phonon number that makes it possible to gain the parity and spin-forbidden (2) E ( g ) -> (4) A (2g ) transitions rather than an extrinsic effect of lattice thermal expansion. The temperature dependence of the zero-phonon line emission intensity I (ZPL) may be a good indicator for deciding whether an observed anomaly of I (PL) is due to an intrinsic or an extrinsic effect because its intensity should in principle not be dependent on T. The experimental data on the Rb2GeF6:Mn4+ fluoride and Cs2WO2F4:Mn4+ oxyfluoride phosphors are presented as a direct verification of this. A discussion is also given on the (2) E ( g ) -> (4) A (2g ) transition properties in connection with the inelastic light scattering spectroscopy.