Degradation of some IR upconverting phosphors by ionizing radiation
Certain materials co-doped with Yb+3 and either Er+3, Ho+3 or Tm+3 are known to be IR upconverting phosphors. We have found that this upconversion property may be easily and controllably degraded in some phosphors by irradiation with electrons, x-rays or shortwave UV. The original state of the phosphor may be restored by a suitable post-treatment. The phenomenon can be used to store, process and display information. A survey of the radiation sensitivity and properties of irradiated upconverting phosphors has been made. It is concluded that electrons and ionizing radiation produce defects that reduce the lifetime of the excited state of the sensitizer (Yb+3) and therefore interfere with the radiationless transfer of energy from the sensitizer to the activator, which is the basis of the upconversion phenomenon.