RESUMO
Here, we report the role of crystallite size and surrounding medium on the upconversion emission of Er3+ in BaTiO3 oxide nanocrystals. The samples were prepared by sol-emulsion-gel method and heat-treated at two different temperatures yielding powders containing nanoparticles of different sizes. Green (550 nm) and red (660 nm) upconversion emission were observed at room temperature from the 4S3/2 and 4F9/2 levels of BaTiO3:Er3+ nanocrystals. The pump power dependence study confirms that all these upconversion emission lines are a two-photon absorption process. We observed that the luminescence lifetime is shorter for the sample containing smaller particles. Optical thermometry experiments were performed in air, water and glycerol in a temperature range from 27.1 up to 47.1 degrees C aiming to use this material as a biological temperature sensor.
RESUMO
We investigated the frequency upconversion (UC) process in BaTiO3:Er3+ nanocrystals for excitation wavelengths in the range 638 to 660 nm. Green upconversion emissions at 526 and 547 nm corresponding to 2H11/2 --> 4I15/2 and 4S3/2 --> 4I15/2 to transitions of the Er3+ were observed. The excitation spectrum for UC emissions presented three bands, due to ground state and excited state absorption of Er3+ ions. The UC intensity as a function of the laser power was investigated and it was found this a two-photon absorption process.