General and Convenient Method for Making Highly Luminescent Sol−Gel Derived Silica and Alumina Films by Using LaF ₃ Nanoparticles Doped with Lanthanide Ions (Er ³⁺ , Nd ³⁺ , and Ho ³⁺ )

Silica films with Ln 3+ -doped LaF 3 nanoparticles were prepared by sol gel method and their luminescent properties were studied as a function of the temperature. Significant improvements in the luminescent properties, in terms of the lifetime for the 4 I 13/2 level of Er 3+ (∼10.9 ms), 4 F 3/2 level of Nd 3+ (∼171 μs), and 5 F 3 level of Ho 3+ (∼6 μs), were obtained when corresponding nanoparticles are incorporated in silica films rather than the bare ions. In addition to the LaF 3 as the low phonon energy matrix, the absence of lanthanide ion clustering, and the increased distance between the OH groups of the silica matrix and the lanthanide ions, are responsible for the observed improvements in the luminescent properties for nanoparticle incorporated silica films. Lifetime values could be further improved by incorporating core−shell nanoparticles (the doped LaF 3 core surrounded by an undoped shell of LaF 3 ) in the silica matrix, as a result of further reduction of the nonradiative pathways.