KNN-based optical temperature sensing ceramics integrating negative thermal quenching and photochromic self-recovery behavior

Superior Energy Storage Capability and Fluorescence Negative Thermal Expansion of NaNbO3‐Based Transparent Ceramics by Synergistic Optimization

“…Figure 9e shows the relative sensitivities of the ceramic with x = 0.03 as a function of temperature. The maximum S r value is 2.693% K −1 (at 233 K), which is competitive compared to previously reported materials, [ 14,15,28,55–60 ] and demonstrates potential application in optical temperature sensing. Here, to explain the phenomenon of fluorescence negative thermal expansion, the energy transfer process between sensitizer (Yb 3+ ) and activator (Tm 3+ ) needs to be further analyzed.…”

“…Each sample exhibits different absorption bands at ≈488, ≈695, and ≈795 nm (Figure 3a), which are from the 1 G 4 → 3 H 6 , 3 F 2 → 3 H 6 and 3 H 4 → 3 H 6 transitions of Tm 3+ , respectively. [ 28 ] In contrast, below the wavelength of ≈400 nm, the measured T % rapidly drops to zero, which can be explained by the inter‐band transition of the ceramics. A Tauc equation can be used to roughly compute the experimental E g in this case.…”

“…When we choose the thermal quenching peak at 488 nm and the thermal enhancement peak at 695 nm, two opposite trends make the FIR values more sensitive to temperature changes (Figure 9d). The FIR value based on blue and red emissions can be fitted using Boltzmann's law: [ 28 ] $$$$\begin{equation}FIR = \frac{{{I}_{695}}}{{{I}_{488}}} = D\exp \left( {\frac{{ - \Delta E}}{{kT}}} \right)\end{equation}$$$$where 𝐼 695 and 𝐼 488 are the emission intensities at 695 and 488 nm, respectively, D is a constant, Δ E is the energy gap of the thermally coupled levels and k is the Boltzmann's constant (8.629 × 10 −5 eV K −1 ). The FIR fitting regression coefficient is shown in Figure 9e, and the COD(R 2 ) value is greater than 99%, proving high adaptability.…”