RESUMO
The luminescence spectra of milk containing rhodamine 6G are shown to exhibit typical signatures of random lasing when excited with 532 nm laser pulses. Experiments carried out on whole and skim forms of two commercial brands of UHT milk, with fat volume concentrations ranging from 0 to 4%, presented lasing threshold values dependent on the fat concentration, suggesting that a random laser technique can be developed to monitor such important parameter.
Assuntos
Gorduras na Dieta/análise , Leite/química , Espectrometria de Fluorescência/métodos , Animais , Corantes Fluorescentes , Lasers de Estado Sólido , Lipídeos/análise , Pasteurização/métodos , RodaminasRESUMO
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.