Double-phase Nd3+, Yb3+:CeF3/CeO2 nanoparticles as potential materials for optical temperature sensing

Abstract

In this work, we study the possibility the use of Nd³⁺, Yb³⁺:CeF₃/CeO₂ nanoparticles in ratiometric luminescence thermometry. In order to explain the mechanism of the luminescence temperature sensitivity, we physically characterized the samples by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), laser spectroscopy, and electron paramagnetic resonance (EPR). In particular, Nd³⁺, Yb³⁺:CeF₃ nanoparticles were synthesized via co-precipitation method and annealed in air at 600 °C for 0, 15, 30, 60, and 120 min to obtain double-phase Nd³⁺, Yb³⁺:CeF₃/CeO₂ nanoparticles as well as single-phase Nd³⁺, Yb³⁺:CeO₂ ones (at 120 min). The physical diameter of the samples gradually increases from 19 ± 2 (doped CeF₃) to 409 ± 18 nm (doped CeO₂). It was suggested, that the double-phase samples consist of sintered doped CeF₃ and CeO₂ nanoparticles having average grain diameter around 65 nm. The single-phase CeO₂ sample also consists of sintered CeO₂ nanoparticles, suggestively. The luminescence intensity ratio (LIR) was analyzed in the 80–320 K range (LIR = I_Nd/I_Yb, where 848–925 nm (⁴F_3/2 – ⁴I_9/2) Nd³⁺ and 925–1048 nm (²F_5/2 – ²F_7/2) Yb³⁺). The maximal relative temperature sensitivity was achieved for Nd³⁺, Yb³⁺:CeO₂ sample (∼0.2 %/K), which is very competitive value. The LIR function has a simple linear temperature dependency in the broad 80–320 K which allows uniquely identifying the temperature at least in the studied broad temperature range. The mechanism of temperature sensitivity was suggested.