Upconverting tri-doped calcium fluoride based thin films: a comparison of MOCVD and sol-gel preparation methods

Starting from fluorinated metal–organic β-diketonates, we report the synthesis of undoped and lanthanide-doped alkaline-earth fluoride (Er3+,Tm3+,Yb3+ tri-doped CaF2) thin films through two different chemical approaches: a metal–organic chemical vapor deposition (MOCVD) method and a combined sol–gel/spin-coating procedure. Both chemical approaches have the advantage of being very reliable and reproducible for the fast production of thin films with a high degree of uniformity over large areas. The fluorinated metal precursors act as a single-source in both processes, and an accurate control of the process parameters allows the optimization of the doped CaF2 films. X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray analysis have been used to characterize the deposited films. Upconversion emission, typical of the lanthanide ions, in the visible and near infrared regions upon laser excitation at 980 nm is clearly observable. The emissions are in the central region of the CIE1931 color coordinate space.