Energy Loss and Energy Storage from the Eu+3 Charge-Transfer States in Y and La Oxysulfides

In and , concentration‐ and temperature‐dependent loss and storage effects are observed for excitation into the Eu +3 charge‐transfer states (CTS) and into certain Eu +3 5 D states. It is shown that the losses and storage both occur from the CTS. They occur for 5 D excitations only as a consequence of the 5 D excitation having reached the CTS through thermally promoted crossovers. The losses and storage are both attributed to the Eu +3 CTS dissociating thermally into Eu +2 plus a free hole. The freed holes are stored in hole traps. If the holes are thermally or IR stimulated back to the Eu +2 centers and reform the Eu +3 CTS, the stored energy is retrieved as Eu +3 line emissions. If the extra electrons at the Eu +2 centers migrate through the Eu activators and recombine nonradiatively at the hole centers, the stored energy is lost.