Ratiometric Luminescent Thermometry with Excellent Sensitivity over a Broad Temperature Range Utilizing Thermally‐Assisted and Multiphoton Upconversion in Triply‐Doped La₂O₃:Yb³⁺/Er³⁺/Nd³⁺

Abstract

A ratiometric optical thermometer based on triply‐doped La2O3:Yb3+/Er3+/Nd3+ microcrystals is reported with a relative sensitivity above 1% K−1 in the entire range from 300–700 K, and is between 1.8–0.7% K−1 over the range 290–833 K. The 825 nm upconversion (UC) emission from the Nd3+ 4F5/2 level relies on thermally‐assisted energy transfer from Yb3+; thus, unusually, the near‐infrared emission increases with increasing temperature in the relevant range. More typically, the two‐photon 660 nm UC from Er3+ 4F9/2 level decreases in intensity with increasing temperature due to increasing non‐radiative rates. The variation of fluorescent intensity ratio between these emissions is amplified by their opposite responses to temperature change leading to excellent sensitivity. Concurrently, the different pathways for the temperature response in the two emitting ions enable the high sensitivity to be maintained over an atypically broad temperature range. The wide separation in wavelength means that a standard silicon‐based monochrome camera with broad (inexpensive) band pass filters is sufficient to use this phosphor for thermography. The concept of combining thermally‐activated UC with classical Stokes‐shifted emission is demonstrated to provide combined features of excellent and broad‐range sensitivity plus excellent repeatability. Materials based on this concept are very promising for optical thermometry.

Detection of Sub‐Terahertz Raman Response and Nonlinear Optical Effects for Luminescent Yb(III) Complexes

“…[28] Additionally, sensitivity is higher for YbS (0.5-0.6% K −1 ) than YbSe (0.4-0.5% K −1 ) in the physiological temperature range. [27] These values are comparable with other reported Yb(III)-based ratiometric thermometers. [29] The other bands exhibit a moderate quality of thermometric performance as the highest calculated sensitivity is found to be 0.5% and 0.1% K −1 for Δ(975/1000), and 0.09% and 0.64% K −1 for Δ(975/1040) intensity ratios for YbS and YbSe, respectively (Figures S18b, S19b, S21b, and S22b, and Table S9, Supporting Information).…”

“…The decline of the hot band intensity and the decreasing emission intensity with temperature reveal that YbS and YbSe can act as a luminescent thermometer for wide temperatures from 100 to 350 K, including a physiological temperature region important for biological applications. [27] The decreasing emission intensity correlates with the excitation spectra with a slight shift of the peak in the lower energy region during cooling (Figure S15, Supporting Information). To better understand the temperature dependence of these peak intensities, the emission spectra were precisely recorded.…”

Optical temperature sensing with an Er3+, Yb3+co-doped LaBMoO6single crystal

“…Since the particle population of 2 H 11/2 and 4 S 3/2 of Er 3+ follows the Boltzmann distribution law, 43,63 the FIR of 2 H 11/2 and 4 S 3/2 states of Er 3+ can be described as follows: 11 where I u and I l are the UC emission intensities of the upper ( 2 H 11/2 ) and lower ( 4 S 3/2 ) energy levels, respectively; Δ E is the energy gap between the TCELs; K B and T denote the Boltzmann constant and absolute temperature, respectively; A is a pre-exponential coefficient affected by factors such as the intensity of such as spontaneous emission transition rate and fluorescence branch ratio, which can be expressed aswhere v i is the frequency of the radiation, β ij is the luminescence branching ratio, A ij is the spontaneous radiation transition rate and g i is the level degeneracy. The parameter A is generally regarded as a constant.…”

“…Besides the temperature sensing range, the temperature sensitivity coefficients such as absolute temperature sensitivity coefficient S a and relative temperature sensitivity S r are crucial parameters to estimate the temperature sensing performance of optical thermometry. The values of S a and S r are calculated according to the following equations: 63,65 …”

NaSr2Nb5O15:Yb3+, Ho3+, Tm3+ transparent glass ceramics: Up‐conversion optical thermometry and energy storage property

“…RE ions with TCEL energy gap close to 2000 cm −1 are selected to obtain high S r . 7,[9][10][11][12] Among the lanthanide ions, the 3 F 2,3 and 3 H 4 energy levels of Tm 3+ (∼2000 cm −1 ) are preferred. Unique, a large number of experiments show that the emission band ( 3 F 2,3 → 3 H 6 ) of Tm 3+ has the opposite temperature dependence to other emission bands under the excitation of 980 nm.…”