Abstract

We report the use of a sensitive spectrometer system in studying sharp optical absorption lines of transitions between 4f³ crystal-field levels of Nd³⁺ in NdF₃ films as thin as one monolayer. Epitaxial films as thin as 5 nm on GaAs substrates displayed absorption lines with asymmetric line shapes because of dispersion at the lines and surface reflections. Samples with an antireflecting buffer layer between the NdF₃ layer and the substrate allowed observation of crystal-field lines in films as thin as 0.36 nm (0.5 unit cells). In the thinnest films, lines from the ⁴I_9/2 → ⁴G_5/2 transition were shifted to the blue by 6 cm^-1 relative to their positions in thicker films, and the splitting of the two strongest components increased from 8.4 to 14.4 cm^-1 as a result of lattice distortion by the buffer layer.

© 1990 Optical Society of America