Lanthanide Upconverted Luminescence for Simultaneous Contactless Optical Thermometry and Manometry–Sensing under Extreme Conditions of Pressure and Temperature

[Image: see text] The growing interest in the miniaturization of various devices and conducting experiments under extreme conditions of pressure and temperature causes the need for the development of small, contactless, precise, and accurate optical sensors without any electrical connections. In this work, YF(3):Yb(3+)-Er(3+) upconverting microparticles are used as a bifunctional luminescence sensor for simultaneous temperature and pressure measurements. Different changes in the properties of Er(3+) green and red upconverted luminescence, after excitation of Yb(3+) ions in the near-infrared at ∼975 nm, are used to calibrate pressure and/or temperature inside the hydrostatic chamber of a diamond anvil cell (DAC). For temperature sensing, changes in the relative intensities of the Er(3+) green upconverted luminescence of (2)H(11/2) and (4)S(3/2) thermally coupled multiplets to the (4)I(15/2) ground state, whose relative populations follow a Boltzmann distribution, are calibrated. For pressure sensing, the spectral shift of the Er(3+) upconverted red emission peak at ∼665 nm, between the Stark sublevels of the (4)F(9/2) → (4)I(15/2) transition, is used. Experiments performed under simultaneous extreme conditions of pressure, up to ∼8 GPa, and temperature, up to ∼473 K, confirm the possibility of remote optical pressure and temperature sensing.