Abstract:
The polarised two-photon (IR) and one-photon (visible) luminescence excitation spectra of Nd3+ nanoclusters in CaF2 and SrF2 crystals are measured at 10 K using a F2-:LiF colour centre laser tunable in spectral ranges 1090 – 1230 nm and 545 – 615 nm with an emission linewidth of ~0.02 – 0.03 cm-1, an average output power of ~55 mW, and a pulse repetition rate of 10 Hz. The two-photon excitation spectra at the 4I9/2 → 4G5/2 transition reveal the structure, which is absent upon one-photon excitation, which can be explained by different selection rules for some Stark – Stark transitions upon one- and two-photon absorption.