Excited State Absorption for Ratiometric Thermal Imaging.

Luminescence thermometry, an alternative to thermal imaging using the thermovision technique, requires the development of new approaches and a thorough understanding of the physical phenomena involved, in order to improve the temperature readout parameters. A phenomenon that has recently been shown to cause an extremely strong increase in the emission intensity for the temperature elevation is the thermally induced excited state absorption. This work demonstrates that taking advantage of the strong thermal dependence of the thermally induced excited state absorption process, the limitation associated with the two thermally coupled excited levels usually involved in the ratiometric temperature readout can be overcome, improving the thermometric properties of the luminescent thermometer.

Cr based nanocrystalline luminescent thermometers operating in a temporal domain.

Cr3+ doped nanocrystals were examined as a noncontact temperature sensor in a lifetime-based approach. The impact of both the analysis protocols and host materials on the lifetime-based approach was systematically investigated. Temperature-dependent luminescence decay curves were analyzed according to three different procedures (average lifetime approach, double exponential fit and time-gated ratiometric approach).

Implementing Defects for Ratiometric Luminescence Thermometry.

In luminescence thermometry enabling temperature reading at a distance, an important challenge is to propose new solutions that open measuring and material possibilities. Responding to these needs, in the nanocrystalline phosphors of yttrium oxide YO and lutetium oxide LuO, temperature-dependent emission of trivalent terbium Tb dopant ions was recorded at the excitation wavelength 266 nm. The signal of intensity decreasing with temperature was monitored in the range corresponding to the D → F emission band.

Enhancement of the sensitivity of single band ratiometric luminescent nanothermometers based on Tb ions through activation of the cross relaxation process.

The description of luminescent processes and their thermally induced changes, that may be also influenced by the optically active ions concentration, and thus by the various inter-ionic processes, is the key to the improved development of luminescence thermometry. A phosphor doped with only trivalent terbium ions was described, which, by using two excitation lines fitted to the F → D and F → D transitions, shows a luminescent signals with the opposite characteristics of intensity changes as a function of temperature. By modifying the concentration of Tb ions, the probability of {D, F} ↔ {D, F} cross-relaxation was being altered, which turned out to have a beneficial effect on the properties of the described nanothermometers.

Phosphor-Assisted Temperature Sensing and Imaging Using Resonant and Nonresonant Photoexcitation Scheme.

Phosphor-assisted luminescent thermometry relies on studying, often subtle, temperature-dependent spectral properties, such as luminescence spectra, bands shifts, or luminescence lifetimes. Although this is feasible with high-resolution spectrometers or time-resolved detectors, technical implementation of such temperature mapping or wide-field imaging is complex and cumbersome. Therefore, a new approach for noncontact ratiometric temperature detection has been proposed based on comparison of emission properties of bright Cr-doped phosphors at single emission band upon two, resonant and nonresonant, optical excitation bands.