Spectral properties and quantum efficiency of optical emission in rare earth doped crystals

We have studied the spectral properties of Pr3+ -doped CaAl4O7 and SrAl4O7 crystals at 77 and 290 K. Emissions from the 4f5d band are detected using two-photon stepwise excitation. We demonstrated a new method to conveniently measure the quantum efficiency of deep UV emission using the two-step excitation and the difference of the integrated spectral intensities. The quantum efficiencies of the emission from the lowest 4f5d state in the two systems have been estimated and are less than 10% at room temperature. The effect of excited state absorption of the lowest 4f5d on the measurement of the quantum efficiency is analyzed. The actual efficiency may be higher when the effect is taken into account, especially under the condition of strong excitation