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Noninvasive sensing of temperature and pressure offers new and exciting opportunities to investigate and monitor the variation of physicochemical and spectroscopic properties of materials under extreme conditions. In this work, Tm2+‐doped SrB4O7 phosphor material—a novel, contactless bifunctional, and multimodal optical sensor for pressure and temperature is reported. A series of SrB4O7: xTm2+ samples are synthesized via a high‐temperature solid‐state method in air. The impact of high pressure (up to ≈13 GPa) and temperature (from 10 to 400 K) on spectroscopic properties of SrB4O7:Tm2+ is investigated. The emission band of Tm2+ demonstrates a significant spectral shift and a band broadening as a function of both pressure and temperature. Such a result is a consequence of a significant change of vibronic components of the Tm2+ 4f125d ↔ 4f13 zero‐phonon line. The emission bandwidth and its spectral position exhibit excellent sensitivities to pressure, that is, ≈23.17 and ≈−11.85 cm−1 GPa−1, respectively. Furthermore, for the first time, it is shown that temperature sensing can be realized via four different pathways in a single material: i) bandwidth, ii) band shift, iii) band intensity ratio, and iv) luminescence lifetime, with maximal sensitivities of ≈3.85 cm−1 K−1, 1.44 cm−1 K−1, 1.48% K−1 and 4.16% K−1, respectively.

Giant enhancement of optical response of the luminescent pressure sensor SrB4O7:Sm2+, co-doped with Eu2+, caused by effective Eu2+ → Sm2+ energy transfer.

of high sensitivity has become a continuously more important and challenging task, as increasing demand for both industrial development and various scientific research purposes. However, the conventional thermometers based on the expansion of liquids or metals, such as mercurial thermometer, thermocouples or pyrometers suffer from several shortages, such as: limited spatial resolution (inability to detect the temperature of an object with the scale below 10 µm), often necessity of physical contact, low sensitivity, and so forth. [2] Recently, the remote thermo-vision (thermal imaging) technique at nano-or micro-scale has been attracting increasing interest of the researchers and industry. This imaging technique has been more frequently used, since it allows immediate temperature readouts and thermal mapping in biological systems (in vivo), which is also beneficial for preventing damage of the biological, mechanical or electronic components. [3][4][5] Luminescence thermometry, as an alternative to the thermo-vision technique, provides the opportunity to also detect temperature in a non-invasive way, with higher sensitivity, better spatial resolution and rapid response. However, new routes of designing novel luminescent thermometers are required to overcome the existing technical drawbacks and to improve the temperature sensing performance.The concept of optical temperature sensing using band intensity ratio is considered as one of the most effective, self-reference, non-invasive, and rapid detection techniques for the local temperature in natural or engineered systems. In this work, for the first time a divalent lanthanide-co-doped dual-center system, i.e., SrB 4 O 7 :Eu 2+ /Sm 2+ phosphors, working as a bifunctional ratiometric sensor of temperature and pressure is employed. With temperature alterations, the Eu 2+ /Sm 2+ luminescence intensity ratio and the emission lifetime of Sm 2+ are significantly changed, showing unprecedentedly high relative sensitivity of 45.6 and 3.17% K -1 , respectively. Moreover, in the pressure range from ≈10 to 40 GPa, the intensity ratio of the Eu 2+ /Sm 2+ emissions shows strong pressure dependence and can be utilized for pressure monitoring, with high pressure relative sensitivity of ≈13.8% GPa -1 . The superior performance indicates that the developed dual-center Eu 2+ /Sm 2+ -codoped SrB 4 O 7 phosphors are promising candidates for supersensitive optical sensing applications. The findings open a new approach of designing optical temperature and pressure sensors.

Nonlinear optical spectroscopy may be a powerful tool for sensing of various intrinsic properties of materials and different state functions of the system. This is due to the strong dependence of nonlinear phenomena on numerous physicochemical factors. The feasibility of simultaneously employing the second harmonic generation (SHG) and upconversion luminescence (UCL) processes in BaTiO3:Ho3+,Yb3+ for optical temperature sensing is demonstrated for the first time. Under 976 nm laser excitation, the evolution of the SHG and UCL band intensity ratio is correlated with temperature and calibrated within the temperature range of 25–305 °C. The band intensity ratio between SHG and UCL exhibits a sigmoidal dependence on temperature, and, hence, it can allow the detection of phase transitions from non‐centrosymmetric to centrosymmetric systems, and vice versa. Most importantly, from the perspective of optical temperature sensing, this work provides a novel and effective strategy for nonlinear optical thermometry, with high sensitivity of up to 2.78% °C–1.

A new strategy for noninvasive temperature probing, applying the temperature-induced configuration crossover between the thermally-coupled 6P7/2 and 5d1 levels of Eu2+ is presented.

To address the unsatisfactory pressure sensitivity of luminescent manometers, Eu2+‐activated supersensitive microspheres operating in the visible range are developed. A series of Eu2+‐doped Sr8Si4O12Cl8 materials are synthesized as microspheres, and their structural and spectroscopic properties are studied theoretically and experimentally. Excited at 350 nm, the samples emit a bright cyan luminescence at ambient conditions that, upon pressure, changes to green emission and finally to yellow light above 7 GPa. Most importantly, a huge red‐shift of the emission band from 497.3 to 568.8 nm is observed as the pressure increases, leading to an ultrahigh‐pressure sensitivity of 9.69 nm/GPa, which is the highest sensitivity ever reported. The designed microspheres with polychromatic emissions and high‐pressure sensitivity are suitable for visual optical pressure sensing, and the applied strategy provides some important guidelines for the development of new optical manometers, allowing pressure monitoring with unprecedented accuracy.