Raman characterization and photoluminescence properties of La1-xTbxPO4·nH2O and La1-xTbxPO4 phosphor nanorods prepared by microwave-assisted hydrothermal synthesis

Abstract The effect of the Tb 3+ –doping content (in the range 0–100 mol%) on the structure (using Raman spectroscopy) and photoluminescence (PL) properties of both rhabdophane-type La 1- x Tb x PO 4 · n H 2 O and monazite-type La 1- x Tb x PO 4 single-crystal nanorods was investigated. La 1- x Tb x PO 4 · n H 2 O was directly obtained by microwave-assisted hydrothermal synthesis and La 1- x Tb x PO 4 by calcination of La 1- x Tb x PO 4 · n H 2 O at 700 °C in air for 2 h. It was found that the characteristic Raman bands shift to higher wavenumbers and become broader with increasing Tb 3+ concentration, which is attributed to attendant unit-cell volume reduction. The PL due to the Tb 3+ f-f transitions has been studied with continuous and pulsed excitations. The PL intensity increases with doping and is maximum for La 0.80 Tb 0.20 PO 4 · n H 2 O and La 0.85 Tb 0.15 PO 4 , i.e., for rhabdophane and monazite-type structures, respectively. A quenching effect is detected for concentrations below x =0.05, but constant efficiency is obtained at higher doping. The calcination increases the efficiency by a factor around 2 due to the combined effects of water molecules and defect elimination. The PL decay curves reveal a long lifetime attributable to single Tb 3+ ions which is almost independent of doping for monazite nanorods (5–4.5 ms), and a shorter one around 0.2 ms most likely due to Tb 3+ dimmers.