Rod-shaped NaY(MoO4)2:Sm3+/Yb3+ nanoheaters for photothermal conversion: Influence of doping concentration and excitation power density

Thermal effect of rare earth (RE) ions doped nanoparticles under near-infrared light irradiation has been underestimated, because main interest and efforts still fall into the distinctive up-converting luminescence property of these particles. In this work, we demonstrate an approach to convert 980 nm light energy to heat energy via a designed nanoheater which is Sm3+/Yb3+ codoped NaY(MoO4)2 nanorods derived from a microwave-assisted hydrothermal reaction. To inspect the photothermal conversion effect of the nanoheaters, Er3+/Yb3+ codoped NaY(MoO4)2 nanorods are prepared via the same synthesis route. A convenient strategy, in which NaY(MoO4)2:Er3+/Yb3+ nanorods are used as nanothermometer, is proposed to monitor the laser-induced temperature change of the nanoheaters by mixing a small amount of nanothermometer with nanoheater. The influence of Sm3+/Yb3+ concentrations and excitation power density on the final temperature of the nanoheaters is studied. It is found that when Yb3+ concentration is fixed to be 10 mol%, the influence of increasing Sm3+ concentration on the photothermal conversion effect is limited; but when Sm3+ is fixed to be 5 mol%, the photothermal conversion is enhanced greatly with the increase of Yb3+ concentration. In addition, the temperature for all the NaY(MoO4)2:Sm3+/Yb3+ nanoheaters after laser irradiation is linearly dependent on the excitation power density. In order to examine the photothermal conversion effect of the nanoheater in liquid media, the PVP (polyvinyl pyrrolidone) solution is used for accommodating the nanoheaters, and effective photothermal conversion is observed.