We have investigated the luminescence of CaF₂ thin films doped with very low concentrations of Sm²⁺ ions using scanning confocal optical microscopy at low temperatures. The film morphology was studied independently by atomic force microscopy. The Sm²⁺ ions are homogeneously distributed in the films and show photobleaching. Unexpectedly, on the film surface strongly luminescent small topographic features are observed that are found to contain Sm³⁺ by spectral analysis. The formation of Sm³⁺ is probably due to the presence of oxygen during film growth. In the lowest doped films on-off blinking behavior of isolated luminescent spots provides strong evidence for the first observation of single ions in a crystal.

Persistent spectral hole burning was performed on the ⁷F₀–⁵D₁ transition of Sm²⁺ in thin films of SrFCl. Depending on the substrate and the growth conditions, a total hole depth between 47% and 70% was reached. The holes were Lorentzians of width 4(±0.3) cm^−1. The time evolution of the hole depth was studied. It is described by two exponentials: a short time decay (t₁ = 0.37 days) and a long time decay (t₂ = 20.4 days) with a 20% infinite time limit. One- and two-photon burning mechanisms act.

Multicomponent thin films with spectral hole burning capacity at room temperature were synthesized by using molecular beam and pulsed laser deposition techniques All materials were activated by Sm²⁺ in low-symmetry alkaline earth sites, the synthesis involved the control of ionic diffiision rate during multilayer growth and special reduction of Samarium. Enhancement of hole burning rate by 1-2 orders is obtained in nanocrystalline films as compared to bulk and microcrystalline materials New hypothetic mechanism involving the creation of Sm-defect (photochromic) centers is proposed for reversible photoburning.