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We demonstrate a potential optical thermometric material, Pr3+-doped triple-layered perovskite Na2La2Ti3O10 microcrystals, which promises a remarkable performance in temperature sensing over a wide temperature range (125–533 K), with a maximum relative sensitivity of 2.43% K–1 at 423 K. Both temperature and high-pressure dependent photoluminescence measurements were performed for this compound. It turns out that the Pr3+–Ti4+ intervalence charge transfer state is the primary cause for the very efficient thermometric characteristics in the 296–533 K range. In the 125–300 K range, 3P1 and 3P0 levels of Pr3+ can be exploited as thermally coupled energy levels for temperature sensing with high sensitivity at and below room temperature. A significant enhancement of the Pr3+ ions’ luminescence observed in the 4.5–300 K range is ascribed to an efficient, thermally activated energy transfer process from the host to Pr3+ ions. Carrier recombination on Pr3+ related hole traps was proposed in the studied system. The thermoluminescence properties are investigated, and possible mechanisms for the interpretation of the experimental results are discussed as well. This work may provide a perspective approach to design a high-performance, self-calibrated optical thermometer operating over a wide temperature range.

In this work, the temperature and high-pressure behaviors of Mn 3+ -doped garnet-type Ca 3 Ga 2 Ge 3 O 12 single crystals have been investigated by means of photoluminescence and Raman spectroscopy, respectively. The Jahn−Teller stabilization energy in the 5 E ground state was found to be 1630 cm −1 , being as much as 6 times greater than that in the 5 T 2 excited state, that is, 237 cm −1 . The room-temperature emission spectrum is dominated by the spin-allowed 5 T 2 → 5 E transition at 670 nm upon 532 nm excitation. The temperature dependences of photoluminescence spectra and time decays reveal strong thermalization between 5 T 2 and 1 T 2 levels. Cooling to 50 K empties the 5 T 2 level by virtue of multiphonon transition to the lower-lying 1 T 2 level. As a result, the 1 T 2 → 3 T 1 / 5 E electric-dipole transitions are induced by coupling to odd-parity phonons. The existence of a small amount of Mn 4+ can be ascertained by lowering the temperature or applying high pressure. Upon compression up to 100 kbar, the 5 T 2 → 5 E transition of Mn 3+ undergoes a blue shift at a rate of ∼10.5 cm −1 /kbar. Since both 5 T 2 and 1 T 2 have inverse crystal field dependences, the quenching process from the 5 T 2 level becomes stronger under high pressure. Cryogenic luminescence ratiometric thermometry based on the diverse thermal quenching behaviors of Mn 3+ and Mn 4+ was explored. Furthermore, theoretical calculations employing the exchange-charge model of crystal field for Mn 3+ and Mn 4+ ions in Ga 3+ octahedral sites (C 3i ) in garnet-type Ca 3 Ga 2 Ge 3 O 12 remain in perfect agreement with the experimental data.