Temperature dependence of the line shapes of two-photon excited transitions in KMgF3 : Eu2+

The two-photon excitation line shapes of f-f transitions of Eu2+ in KMgF3 have been investigated as a function of temperature. Results for several transition lines of the P-6(J) and D-6(J) multiplets are presented in this work. The two-photon excited transitions appear as zero-phonon lines with a Lorentzian profile whose peak energy is shifted from the zero temperature position. The observed temperature dependence of the zero-phonon line shapes is ascribed to the elastic scattering of the electronic transitions among vibrational states via anharmonic coupling to a phonon mode of the lattice heat-bath. In those components of 4f(7) multiplets whose energies are not resonant with the 4f(6)5d broad excited state, a direct proportionality to the phonon occupation number of the coupled mode is found for the line-shapes and peak-positions temperature dependences.