RESUMO
While temperature measurements with nanometric spatial resolution can provide valuable information in several fields, most of the current literature using rare-earth based nanothermometers report ensemble-averaged data. Neglecting individual characteristics of each nanocrystal (NC) may lead to important inaccuracies in the temperature measurements. In this work, individual Yb3+/Er3+ codoped yttria NCs are characterized as nanothermometers when embedded in different environments (air, water and ethylene glycol) using the same 5 NCs in all measurements, applying the luminescence intensity ratio technique. The obtained results show that the nanothermometric behavior of each NC in water is equivalent to that in air, up to an overall brightness reduction related to a decrease in collected light. Also, it was observed that the thermometric parameters from each NC can be much more precisely determined than those from the "ensemble" equivalent to the set of 5 single NCs. The "ensemble" parameters have increased uncertainties mainly due to NC size-related variations, which we associate to differences in the surface/volume ratio. Besides the reduced parameter uncertainty, it was also noticed that the single-NC thermometric parameters are directly correlated to the NC brightness, with a dependence that is consistent with the expected variation in the surface/volume ratio. The relevance of surface effects also became evident when the NCs were embedded in ethylene glycol, for which a molecular vibrational mode can resonantly interact with the Er3+ ions electronic excited states used in the present experiments. The methods discussed herein are suitable for contactless on-site calibration of the NCs thermometric response. Therefore, this work can also be useful in the development of measurement and calibration protocols for several lanthanide-based nanothermometric systems.
RESUMO
We report an alternative random laser (RL) architecture based on a flexible and ZnO-enriched cellulose acetate (CA) fiber matrix prepared by electrospinning. The electrospun fibers, mechanically reinforced by polyethylene oxide and impregnated with zinc oxide powder, were applied as an adsorbent surface to incorporate plasmonic centers (silver nanoprisms). The resulting structures - prepared in the absence (CA-ZnO) and in the presence of silver nanoparticles (CA-ZnO-Ag) - were developed to support light excitation, guiding and scattering prototypes of a RL. Both materials were excited by a pulsed (5 Hz, 5 ns) source at 355 nm and their fluorescence emission monitored at 387 nm. The results suggest that the addition of silver nanoprisms to the ZnO- enriched fiber matrix allows large improvement of the RL performance due to the plasmon resonance of the silver nanoprisms, with ~80% reduction in threshold energy. Besides the intensity and spectral analysis, the RL characterization included its spectral and intensity angular dependences. Bending the flexible RL did not affect the spectral characteristics of the device. No degradation was observed in the random laser emission for more than 10,000 shots of the pump laser.
