“Roller coaster”-like thermal evolution of the Er 3+ ion’s red photoluminescence in CaWO 4 :Yb 3+ /Er 3+ phosphors

The abnormal “roller coaster”-like thermal evolution of the Er3+ ion’s red photoluminescence (corresponding to the F9/24−I415/2 transition) in CaWO4:Yb3+/Er3+ phosphors is observed. This red emission suffers from a strong thermal quenching in the 293–573 K temperature range, followed by a sharp increase on further increasing the temperature. The mechanism behind this phenomenon is confirmed to be from the dynamic temperature-dependent multiple mechanisms imposed on the F9/24 state. At relatively low temperatures, the two-photon upconversion mechanism plays a leading role while, with the increasing of temperature, the one-photon channel, ascribed to the thermal population from the lower I9/24 state, gradually takes a dominant place.