Effects of electron beam current density and temperature on peak height ratios 5Dj/5D0 for cathodoluminescence of Ln2O2S:Eu3+

The change in the initial and steady state (∼0 and 5 s after initiation of electron beam irradiation) peak heights from the 5D2⇒7F3, 5D1⇒7F3 and 5D0⇒7F2 cathodoluminescent transitions from Eu3+ have been studied for Ln2O2S:Eu3+ (Ln=La, Gd) phosphors. Specifically, the intensity ratio of these transitions, designated as 5D1/5D0, increased and then decreased for both La2O2S:Eu3+ (0.1 mole%) and Gd2O2S:Eu3+ (0.4 mole%), as the current density was changed from 10 towards a 1000 μA/cm2. These effects were shown to be consistent with feeding from the higher 5D2 excited state to the lower energy 5D1 excited state, resulting in an increase of the 5D1/5D0 ratio at low current densities. At higher current densities, energy was funneled from the 5D1-5D0 states, resulting in a decrease of the 5D1/5D0 ratio. These effects of feeding versus funneling were dependent on both the Eu3+ concentration and current density, and changed with time (i.e., approached a steady state after ∼5 s) due to increased activator interactions from induced internal electric fields. The magnitude of thermal quenching versus interaction quenching was investigated using changes of the peak height ratios of 5D2/5D0 and 5D1/5D0.