This review discusses how low-energy, valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resolution. Electron microscopes are capable of focusing electron beams on sub-nanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theoretical frameworks suited to calculate the probability of energy loss and light emission (cathodoluminescence) are revisited and compared with experimental results. More precisely, a quantum-mechanical description of the interaction between the electrons and the sample is discussed, followed by a powerful classical dielectric approach that can be in practice applied to more complex systems. We assess the conditions under which classical and quantum-mechanical formulations are equivalent. The excitation of collective modes such as plasmons is studied in bulk materials, planar surfaces, and nanoparticles. Light emission induced by the electrons is shown to constitute an excellent probe of plasmons, combining sub-nanometer resolution in the position of the electron beam with nanometer resolution in the emitted wavelength. Both electron energy-loss and cathodoluminescence spectroscopies performed in a scanning mode of operation yield snap shots of plasmon modes in nanostructures with fine spatial detail as compared to other existing imaging techniques, thus providing an ideal tool for nanophotonics studies.

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Optical excitations in electron microscopy

A novel high excited state energy transfer pathway to overcome the phonon quenching effect in rare-earth (RE) oxide upconversion (UC) materials is reported. In Er(Tm)-Yb oxide systems, an extraordinary enhancement of UC luminescence efficiency with four orders of magnitude is realized by Mo co-doping. The RE oxides with significant UC efficiency are successfully utilized for temperature sensing and in vivo imaging.

Temperature Sensing and In Vivo Imaging by Molybdenum Sensitized Visible Upconversion Luminescence of Rare‐Earth Oxides

Accurate and reliable temperature measurement of many special inaccessible objects is a challenging task. Optical temperature sensing is a promising method to achieve it. The current status of optical thermometry of rare-earth ion doped phosphors is reviewed in detail. Based on the mechanisms of optical temperature sensing of different phosphors, temperature dependent luminescence spectra, the fluorescence intensity ratio technique in the data fitting process, and errors of the energy difference between thermally coupled levels, we describe the recent developments in the use of optical thermometry materials. The most important results obtained in each case are summarized, and the main challenges that we need to overcome are discussed. Research in the field of phosphor sensors has shown that they have significant advantages compared to conventional sensors in terms of their properties like greater sensitivity, freedom from electromagnetic interference, long path monitoring, and independence of compatibility with electronic devices.

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Optical temperature sensing of rare-earth ion doped phosphors

Luminescent ratiometric thermometers combining high spatial and temporal resolution at the micro- and nanoscale, where the conventional methods are ineffective, have emerged over the last decade as an effervescent field of research, essentially motivated by their potential applications in nanotechnology, photonics, and biomedicine. Among the distinct luminescent thermal probes, lanthanide-based materials play a central role in the field due to their unique thermometric response and intriguing emission features (eg, high quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, and ligand-dependent luminescence sensitization). This chapter offers a general overview of recent examples of single- and dual-center Ln3 +-based thermometers, emphasizing those working at nanometric scale, being focused on how to quantify their performance accordingly to the relevant parameters: relative sensitivity, temperature uncertainty, spatial and temporal resolution, repeatability (or test–retest reliability), and reproducibility. The emission mechanisms supporting single- and dual-center emissions are reviewed, together with the advantages and limitations of each approach. Illustrative examples of the rich variety of systems designed and developed to sense temperature are provided and explored. Finally, we discuss the challenges and opportunities in the development of highly sensitive luminescent ratiometric thermometers that are currently facing the scientists in this exciting research field.

Lanthanides in Luminescent Thermometry

Development of ion-implanted optical waveguides in optical materials: A review

Temperature dependent emission spectra and decay times of trivalent dysprosium (Dy3) activated Y4Al2O9 (YAM) crystals have been studied for the first time (to our knowledge) The ratio of emission lines intensity can be used in temperature measurements, as it is not dependent on the variability of absolute intensity The Boltzmann model was applied for modeling the temperature variation of the 4I15/2 and 4F9/2 states emissions relative intensities 455 and 481 nm, respectively The calculated approximation gives highest sensor sensitivity of about 3×10(-3)°C-1 for the 600°C-800°C range, which allows for an expectation of usefulness of Dy3+:YAM in high-temperature luminescence thermometry Also, the measured decay times are suitable for temperature sensing

Blue emissions in Dy3+ doped Y4Al2O9 crystals for temperature sensing.

Optical transitions of Ho3+ in YAG

The self-organized rodlike microstructure of terbium-scandium-aluminum garnet−terbium-scandium perovskite, Tb3Sc2Al3O12−TbScO3, eutectic crystals has been studied. The growth of the eutectic by the...

M. Kaczkan

Papers

Blue emissions in Dy3+ doped Y4Al2O9 crystals for temperature sensing.

Optical transitions of Ho3+ in YAG

Self-organized, rodlike, micrometer-scale microstructure of Tb3Sc2Al3O12-TbScO3:Pr eutectic

Cooperative emission in Yb3+:YAG planar epitaxial waveguides

Infra-red to visible up-conversion in holmium-doped materials