Nanostructured CaF2:Ln3+ (Ln3+ = Yb3+/Er3+, Yb3+/Tm3+) Thin Films: MOCVD Fabrication and Their Upconversion Properties

Abstract

Calcium fluoride represents one of the most efficient hosts for up-conversion or down-conversion emissions. A simple metal organic chemical vapor deposition approach is applied to the fabrication of CaF2 nanostructured thin films using the fluorinated “second-generation” β-diketonate compound Ca(hfa)2•diglyme•H2O as a Ca-F single-source precursor. The versatility of the process is demonstrated for the fabrication of up-converting Yb/Er or Yb/Tm codoped CaF2 films on Si, quartz, and glass substrates. The Ln(hfa)3•diglyme (Ln = Tm, Er, Yb) precursors are used as sources of the doping ions. Structural, morphological, and compositional characterization of the films shows the formation of polycrystalline CaF2 films with a very uniform surface and suitable doping. In fact, an appropriate tuning of the mixture composition, i.e., the Ca:Ln ratio in the multicomponent source, permits the deposition of films with the desired stoichiometry. The films show promising up-conversion properties in the visible and near infrared regions upon laser excitation for both doping mixtures.