RESUMO
Colloidal semiconductor nanomaterials present broadband, with large cross-section, two-photon absorption (2PA) spectra, which turn them into an important platform for applications that benefit from a high nonlinear optical response. Despite that, to date, the only means to control the magnitude of the 2PA cross-section is by changing the nanoparticle volume, as it follows a universal volume scale, independent of the material composition. As the emission spectrum is connected utterly to the nanomaterial dimensions, for a given material, the magnitude of the nonlinear optical response is also coupled to the emission spectra. Here, we demonstrate a means to decouple both effects by exploring the 2PA response of different types of heterostructures, tailoring the volume dependence of the 2PA cross-section due to the different dependence of the density of final states on the nanoparticle volume. By heterostructure engineering, one can obtain 1 order of magnitude enhancement of the 2PA cross-section with minimum emission spectra shift.
RESUMO
Optical fiber sensors incorporating luminescent materials are useful for detecting physical parameters and biochemical species. Fluorescent materials integrated on the tips of optical fibers, for example, provide a means to perform fluorescence thermometry while monitoring the intensity or the spectral variations of the fluorescence signal. Similarly, certain molecules can be tracked by monitoring their characteristic emission in the UV wavelength range. A key element for these sensing approaches is the luminescent composite, which may be obtained upon allocating luminescent nanomaterials in glass or polymer hosts. In this work, we explore the fluorescence features of two composites incorporating lanthanide-doped fluorescent powders using polydimethylsiloxane (PDMS) as a host. The composites are obtained by a simple mixing procedure and can be subsequently deposited onto the end faces of optical fibers via dip coating or molding. Whereas one of the composites has shown to be useful for the fabrication of fiber optic temperature sensors, the other shows promising result for detection of UV radiation. The performance of both composites is first evaluated for the fabrication of membranes by examining features such as fluorescent stability. We further explore the influence of parameters such as particle concentration and density on the fluorescence features of the polymer blends. Finally, we demonstrate the incorporation of these PDMS fluorescent composites onto optical fibers and evaluate their sensing capabilities.
RESUMO
The spectroscopic properties of lanthanide ions stem from absorption and emission radiation in the solar spectrum range, which promotes numerous applications in areas such as white light emission, bio-imaging, biological markers, and photovoltaic cells, among others. To intensify these properties, several matrixes have been studied, particularly the yttrium vanadate matrix due to its structural, mechanic, and physicochemical properties. The non-hydrolytic sol-gel process is a versatile way to prepare inorganic oxides doped with lanthanide ions. In this work, we describe the synthesis of yttrium vanadate matrixes doped with Eu3+, Er3+, and/or Yb3+ ions (containing 1% lanthanide ions with respect to Y3+ (molar ratio)) by the non-hydrolytic sol-gel, annealed at 800 °C for 4 h, and their characterization by X-ray diffraction and photoluminescence spectroscopy. The X-ray diffraction patterns display the peaks corresponding to the yttrium vanadate tetragonal phase. Laser excitation at 980 nm elicits Er3+ emission bands in the green and red regions and Eu3+ emission at 620 nm. Laser excitation at 322 nm; i.e., the charge transfer band, provides emission in the same regions, as well as infrared emission. This system is a promising candidate for applications in solar cells, optical amplifiers, and biomarkers because it can be excited at different wavelengths. Graphical Abstract Schematic diagram of the energy level of lanthanides and vanadate ions, and energy transfer.