Relative sensitivity variation law in the field of fluorescence intensity ratio thermometry

Li4 Zn(PO4 )2 :Mn2+ thermosensitive phosphor with dual luminescent centres for optical thermometry

An optical thermometry strategy based on Mn2+ -doped dual-wavelength emission phosphor has been reported. Samples with different doping content were synthesized through a high-temperature solid-phase method under an air atmosphere. The electronic structure of Li4 Zn(PO4 )2 was calculated using density functional theory, revealing it to be a direct band gap material with an energy gap of 4.708 eV. Moreover, the emitting bands of Mn2+ at 530 and 640 nm can be simultaneously observed when using 417 nm as the exciting wavelength. This is due to the occupation of Mn2+ at the Zn2+ site and the interstitial site. Further analysis was conducted on the temperature-dependent emission characteristics of the sample in the range 293-483 K. Mn2+ has different responses to temperature at different doping sites in Li4 Zn(PO4 )2 . Based on the calculations using the fluorescence intensity ratio technique, the maximum relative sensitivity at a temperature of 483 K was determined to be 1.69% K-1 , while the absolute sensitivity was found to be 0.12% K-1 . The results showed that the Li4 Zn(PO4 )2 :Mn2+ phosphor has potential application in optical thermometry.

Multiple ratiometric nanothermometry using semiconductor BiFeO3 nanowires and quantitative validation of thermal sensitivity

Here, we report a very sensitive, non-contact, ratio-metric, and robust luminescence-based temperature sensing using a combination of conventional photoluminescence (PL) and negative thermal quenching (NTQ) mechanisms of semiconductor BiFeO3 (BFO) nanowires. Using this approach, we have demonstrated the absolute thermal sensitivity of ~ 10 mK−1 over the 300–438 K temperature range and the relative sensitivity of 0.75% K−1 at 300 K. Further, we have validated thermal sensitivity of BFO nanowires quantitatively using linear regression and analytical hierarchy process (AHP) and found close match with the experimental results. These results indicated that BFO nanowires are excellent candidates for developing high‐performance luminescence-based temperature sensors.

Graphical abstract

Ratiometric optical thermometry based on temperature-induced shift of V-O charge transfer band edge

Ratiometric optical thermometry was designed using temperature-induced shift of V-O charge transfer band (CTB) edge combined with temperature-induced variation of Tb³⁺ emission in YV_1-xP_xO₄. P was introduced into YVO₄ lattice to form YV_1-xP_xO₄ solid solution successfully, with the purpose of enhancing Tb³⁺ emission. Under 352 nm excitation which locates in the tail of the V-O CTB, emission spectra of YV_0.3P_0.7O₄:Tb³⁺, Eu³⁺/Sm³⁺ were recorded at a series of temperatures ranging from 300 to 440 K. It is demonstrated that Tb³⁺ and Eu³⁺/Sm³⁺ emissions exhibit opposite temperature dependences. The mechanisms for such opposite variations have been interpreted in detail. Based on the varied fluorescence intensity ratio of Eu³⁺/Sm³⁺ to Tb³⁺ with temperature, high relative sensitivity was obtained with a maximal value of 2.85% K^-1 around 365 K. Our results imply that the proposed strategy is a promising candidate for high-sensitive optical temperature sensing.

Highly sensitive fluorescence intensity ratio thermometry by breaking the thermal correlation of two emission centers

Fluorescence intensity ratio thermometry based on hybrid Eu³⁺-doped GdVO₄ and Cr³⁺-doped Al₂O₃ particles has been studied. We aim at overcoming the limitation that the relative sensitivity (S_r) decreases with the square of temperature owing to the thermal relation between the two emitting levels in one matrix in terms of the Boltzmann distribution law. The design of hybrid Eu³⁺-doped GdVO₄ and Cr³⁺-doped Al₂O₃ particles constructs two emission bands with opposite temperature dependences. Furthermore, the S_r makes a breakthrough by obtaining greater sensitivity in a high-temperature range; the maximum value obtained is 1.4%K^-1 at 633 K.