Enhancement of photoluminescence in Er-doped Ag–SiO2 nanocomposite thin films: A post annealing study

Silver–silica (with Ag 2.8 at.% and 8.7 at.%) nanocomposite (NC) thin films doped with Er+3 (0.1–0.9 at.%) were synthesized by atom beam co-sputtering using 1.5 keV Ar atoms. Optical absorption and photoluminescence (PL) studies of pristine and annealed films were performed, together with Rutherford backscattering and secondary ion mass spectroscopy studies for elemental characterization of the NC films. Optical absorption results of pristine and annealed NC film (with Ag ∼8.7 at.%) confirmed the formation of Ag nanoparticles evidenced by the appearance of characteristic surface plasmon resonance absorption features. Photoluminescence (PL) studies, carried out using Ar Laser pumping at 0.488 μm, the wavelength that the Er ions can absorb resonantly, indicated the presence of PL emission around 1.54 μm in the case of all the as-synthesized samples. The observed PL peak corresponds to the atomic transitions of Er as reported in literature. A relative enhancement in the intensity of PL peak has been observed after annealing the NC films. In the case of NC film with 0.9 at.% Er and 8.7 at.% Ag, the enhancement in PL intensity is almost twice, with respect to the as-deposited sample, for a heat treatment of about 1 h at 600 °C in a nitrogen atmosphere. However for a NC film with Er 0.1 at.% + Ag 2.8 at.%, the PL intensity is enhanced by approximately 3.7 times after annealing at 400 °C for 1 h in nitrogen atmosphere. Since the samples with surface plasmon resonance (SPR) did not show the PL enhancement, the role of SPR in the enhancement of the PL is ruled out. The enhanced PL emission from Er and Ag codoped silica indicates that the Er photo-stimulation is mediated by the energy transfer from Ag nanostructures or ions to Er. Lifetimes of PL peaks for the pristine and annealed samples were also studied. The observed lifetime ∼10 ms is a good indication of excellent PL efficiency.

Research highlights
► Synthesis of Er:SiO2 and Er:Ag:SiO2 nanocomposites by atom beam co-sputtering technique.
► Effect of annealing temperature on photoluminescence (PL) intensity is studied in the absence as well as in presence of Ag nanoparticles.
► Enhancement of PL signal is observed for smaller concentration of Er and Ag. The further enhancement of PL signal for the same sample is observed on annealing it at 400 °C.
► Energy transfer mechanism rather than electric field enhancement due to surface plasmon resonance is responsible for enhancement in PL signal.