Excited-state absorption byEu2+in NaF andKMgF3

Excited-state absorption (ESA) has been studied in NaF:${\mathrm{Eu}}^{2+}$ and ${\mathrm{KMgF}}_3$:${\mathrm{Eu}}^{2+}$ using a pump-probe technique in the visible region. The pump fluence dependence of fluorescence and transmission gives evidence of ESA in the ultraviolet. A broad ESA band is observed at wavelengths shorter than about 600 nm in NaF:Eu. Comparison of this result with earlier data on KBr:Eu, KCl:Eu, and NaCl:Eu, and with published photoconductivity data suggests that the ESA is due to photoionization, despite disagreement with the predictions of an electrostatic model for ionization. In ${\mathrm{KMgF}}_3$:Eu no ESA is evident in the visible, but strong ESA is observed at the 193-nm pump wavelength.