Reliability of rare-earth-doped infrared luminescent nanothermometers

Abstract

Rare-earth-doped luminescent nanothermometers are not reliable as their emission spectra can be affected by numerous environmental and experimental factors.

NIR‐II/III Luminescence Ratiometric Nanothermometry with Phonon‐Tuned Sensitivity

“…The S a and S r reach as high as 0.0127 K −1 and 1.01% K −1 at 65 °C, promising their uses in biological applications. It should be noted that the excitation and emissions of nanothermometers show overlap with water absorption bands (especially at around 1500 nm), which will heat biological tissues due to the absorption of NIR photons by water . We further studied the self‐heating of nanothermometers.…”

“…It should be noted that the excitation and emissions of nanothermometers show overlap with water absorption bands (especially at around 1500 nm), which will heat biological tissues due to the absorption of NIR photons by water. [41][42][43] We further studied the self-heating of nanothermometers. The time-dependent temperature profiles of aqueous Y 2 O 3 : 0.5%Ho 3+ , 1%Er 3+ , 3%Yb 3+ nanospheres excited with different power density indicate that if the quantum yield of nanothermometers is high enough, it is possible to ignore the self-heating effect, although the quantum yield of our nanothermometers is 4.7% for NIR-II/III emissions, which is not satisfactory (Figure S15, Supporting Information).…”

Optical Nanoscale Thermometry: From Fundamental Mechanisms to Emerging Practical Applications

“…This means that the measured value might not be an accurate reading of the true temperature, but rather TEN. [25] Effects known to give rise to TEN are, for instance: i) variable response of the nanothermometers to different laser excitation powers, ii) self-absorption by the nanoprobe of its own photoluminescence, iii) wavelengthdependent absorption and scattering of light by the environment, iv) apparent wavelength shifts caused by absorption/emission of the surroundings, which can alter the spectral shape of the signal, and v) heating of the nanosensor either due to laser absorption or nonradiative, phonon-assisted decay processes. These effects can be partially mitigated by, for instance: monitoring the response of the sensor i′) under different excitation powers, ii′) at different depths in the sample, and iii′) off-and in situ-all while temperature is kept constant, to quantify the (sample-specific) TEN.…”

“…Limitations and Sources of TEN: Upconversion nanoparticles are some of the most widely used nanothermometers. A recent report [25] however, has expressed concerns about their reliability as thermosensors due to often-overlooked artifacts that can lead to inaccurate temperature readings. A known issue is the dependence of the rare-earth ions' spectral emission on excitation power.…”

“…Failure to control for these effects can lead to thermal equivalent noise up to several tens of degrees. [25]…”