Band Gap Engineering in Luminescence Thermometry – Pros and Cons

Abstract

Luminescence thermometry and 2D imaging using luminescence thermometric phosphors are of growing interest as these non-contact and non-invasive techniques may offer important advantages in some applications. The requirements such thermometers have to fulfill depend on considered use. It is obvious that bio and medical applications points on different parameters than measurements in cryo-range and measuring high temperatures point on yet different needs. Nevertheless, high-sensitivity and low inaccuracy are always appreciated, as well as chemical stability in conditions the thermometers are to be used.One of the limitations of known luminescence thermometers is their limited range of temperatures they may measure. Obviously, some applications do not need a broad range of thermometer usability. On the other hand, presenting a good performance over a wide range of temperatures would give a versatile “all-purpose” thermometer. This might open a door for truly broad usage of such a phosphor.Trying to deliberately manage the performance of luminescence thermometers for a broad-range and accurate temperature measuring we paid attention to the bandgap engineering as a tool to achieve this goal. In this presentation, we shall focus on Lu2(Ge,Si)O5:Pr and Y3(Al,Ga)5O12:Pr powders with different Ge:Si and Al:Ga ratios, respectively. We shall discuss the advantages of bandgap engineering in luminescence thermometry and will point to possible complications this may cause. Among others, we shall show that managing the bandgap cause at the same time changes in phonons energies and these affect radiative and non-radiative processes, so important when luminescence over a broad range of temperatures is considered. Last but not least, a side effect of bandgap engineering is the change of the phosphor refractive index, also an important parameter for luminescence properties.This research was supported by the Polish National Science Centre (NCN) upon the grants #UMO-2017/25/B/ST5/00824 and UMO-2018/29/B/ST5/00420 and the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by Portuguese funds through the Portuguese Foundation for Science and Technology (FCT)/MCTES. Financial support from FCT (PTDC/CTM-NAN/4647/2014, NANOHEATCONTROL - POCI-01-0145-FEDER-031469) is also acknowledged. E. Z. and L. D. C. are grateful to the Polish National Agency for Academic Exchange (NAWA) for support under the NAWA-Bekker #PPN/BEK/2018/1/00333/DEC/1 and NAWA-Ulam #PPN/ULM/2019/1/00077/U/00001 projects, respectively. Figure 1