Mechanism for energy transfer processes between Ce3+ and Tb3+ in LaPO4:Ce,Tb nanocrystals by time-resolved luminescence spectroscopy

The energy transfer mechanisms between Ce3+ and Tb3+ in LaPO4:Ce,Tb nanocrystals have been studied by means of time-resolved luminescence spectroscopy in a wide temperature range (10–300 K). Special attention was paid to detailed comparative analysis of both rise and decay emission components of both Ce3+ and Tb3+. Surprisingly, a relatively slow rise (several microseconds) of Tb3+ emission under 266-nm laser excitation was detected, which corresponds to the 4f–5d transition of Ce3+ in LaPO4. It was shown that this rise of Tb3+ emission could not have arisen due to relaxation of Ce3+ ions, whose excited state has a lifetime of about 20 ns. It was demonstrated that the generally accepted concept of a resonant energy transfer from Ce3+ to Tb3+ in LaPO4 could not explain the time-resolved luminescence characteristics as well as the observed temperature dependence. Hence, a new concept of the energy transfer process from Ce3+ to Tb3+ in LaPO4 via host lattice states was suggested and elucidated by proposing several possible models.