Excitation and emission processes of Tb3+ in porous anodic alumina

The strong photoluminescence (PL) of porous anodic alumina (PAA) with terbium deposition is reported. PAA, which has a regular pore morphology, is considered an effective template for fabricating luminescent composites. Tb was deposited onto PAA films by immersion in alcoholic solution with terbium chloride followed by heat treatment. The PL spectra demonstrate typical bands of Tb3+ corresponding to 5D4 → 7Fj (j = 3, 4, 5, 6,) electron transition, with the maximum at 18,360 cm−1 (5D4 → 7F5). The PL mechanism of Tb3+ was systematically studied with annealing temperature. The non-radiative relaxation channel is provided by OH hydroxyls at the surface of porous anodic alumina and, after annealing at 900 °C, the PL yield is highly improved. The PL intensity of Tb3+ increases with laser power and a saturation phenomenon, associated with the ratio of Tb3+ to Tb4+ ions, is observed at approximately 90 W/cm2. Based on a theoretical model, the optical cross-section σ of terbium in PAA is estimated, with a value close to that of other porous materials doped with the rare-earth elements.