Energy transfer and storage mechanisms in infrared-sensitive storage phosphor SrS:Eu,Sm

Magnetic susceptibility of storage phosphors Sr:Eu,Sm was studied before, after excitation, and after the stored energy has been exhausted whether by infrared irradiation or by heating. SQUID-magnetometer was used to detect the slightest variations of magnetisation due to energy storage. The old model of charge transformations of both Eu and Sm impurities assumes a decrease of magnetisation after energy storage. However, the measured data contradict with this old model. EPR and Mössbauer studies showed that both divalent and trivalent Eu ions are present in the storage phosphors. The obtained results indicate that energy is stored and released in one complex trapping and luminescence centre. The trapped at Eu3+–vC–Sm3+ complexes exciton is suggested to be responsible for energy storage and transfer to luminescence centres.