For years, various contact techniques were used to measure temperature. Development of novel and evolving technologies raised the interest in elaboration of non-contact thermometry. Nowadays, this is radiation pyrometry which is the method of choice for such purposes. Yet, it has important limitations – sensitivity to stray light or reflected radiation as well as sensitivity to flame interferences. Also accuracy of temperature measurement, which is not better than ~2 K, is not always satisfactory. Today technologies do not fulfill the needs of temperature sensing in microelectronics, microoptics, photonics, microfluidics, nanomedicine and they require alternative solutions.

Among promising approaches, overcoming the limitations of other techniques, luminescent methods are of great interest. While the idea is not new [1], a real breakthrough using this technique was not yet achieved. Combining a high sensitivity and accuracy as well as broad range of temperature usability within one temperature sensor appeared challenging [2,3].

In this presentation we shall prove that Pr³⁺ luminescence characteristics may offer a lot in this field. While in some compositions this ion generates only 4f®4f luminescence due to relaxation of the higher ³P₀ and lower ¹D₂ levels, in some others also 5d®4f luminescence may take place. We explored the possibility to use all these three luminescent components to sense the temperature accurately and in a broad range. The main argument for that is that all the three emissions are characterized by different mechanisms of their thermal quenching. Furthermore, temperature strongly affects the non-radiative relaxation between the three levels. Our presentation will show first results of the approach presented above using data for Sr₂GeO₄:Pr and will prove a validity and potential of this new attitude. Figure 1 presents profound changes in emission spectra of Sr₂GeO₄:Pr in the range of 17-600 K.

[1] P. Neubert, US2085508 A, 1937.

[2] L. D. Carlos, F. Palacio, Thermometry at the Nanoscale: Techniques and Selected Applications, Royal Society of Chemistry, Oxfordshire 2016.

[3] C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millán, V. S. Amaral, F. Palacio, L. D. Carlos, Nanoscale 2012, 4, 4799.