A new thermographic nanocrystalline Sr4Al14O25 :Mn4+, Tb3+ phosphor was developed including the optimization of the concentrations of both dopants and of the synthesis conditions. The combination of the thermally quenched luminescence from the Mn4+ ions to the almost temperature independent emission from Tb3+ provides a sensitive luminescent thermometer (SR=2.8%/oC at 150oC) with strong emission colour variability. In addition, a figure of merit for this luminescence thermochromism was proposed, as the relative sensitivities of the x and y CIE coordinates, which for this phosphor reaches at 150°C SR(x)=0.6%/oC and SR(y)=0.4%/oC, respectively. Non-contact thermal imaging was demonstrated with this phosphor using a single consumer digital camera and exploiting the ratio of red (R) and green (G) channels of the RGB images thereby confirming the high applicative potential of Sr4Al14O25 :Mn4+, Tb3+ nanocrystals for thermal sensing and mapping.

The influence of the crystal field strength and host material composition on the spectral position of the emission band and thermal stability of Fe³⁺luminescence was investigated in order to develop a highly sensitive luminescence thermometer.

From quencher to potent activator – multimodal luminescence thermometry with Fe³⁺ in the oxides MAl₄O₇ (M = Ca, Sr, Ba).

New types of contactless luminescence nanothermometers, namely, LiAl₅O₈:Fe³⁺ and LiAl₅O₈:Fe³⁺, Nd³⁺ are presented for the first time, revealing the potential for applications in biological systems. The temperature-sensing capability of the nanocrystals was analyzed in wide range of temperature (−150 to 300 °C). The emission intensity of the Fe³⁺ ions is affected by the change in temperature, which induces quenching of the ⁴T₁ (⁴G) → ⁶A₁ (⁶S) Fe³⁺ transition situated in the 1st biological window. The highest relative sensitivity in the temperature range (0 to 50 °C) was found to be 0.82% °C (at 26 °C) for LiAl₅O₈: 0.05% Fe³⁺ nanoparticles that are characterized by long luminescent lifetime of 5.64 ms. In the range of low and high temperatures the S_max was calculated for LiAl₅O₈:0.5% Fe³⁺ to be 0.92% °C at −100 °C and for LiAl₅O₈:0.01% Fe³⁺ to be 0.79% °C at 150 °C. The cytotoxicity assessment carried out on the LiAl₅O₈:Fe³⁺ nanocrystals, demonstrated that they are biocompatible and may be utilized for in vivo temperature sensing. The ratiometric luminescent nanothermometer, LiAl₅O₈:Fe³⁺, Nd³⁺, which was used as a reference, possesses an S_max = 0.56%/°C at −80 °C, upon separate excitation of Fe³⁺ and Nd³⁺ ions using 266 nm and 808 nm light, respectively.

Numerous methods are known to improve the relative temperature sensitivity of luminescent thermometers. These methods include optimization of the host material, the size of the nanoparticles, the dopant ion type and concentration, or the excitation intensity and operation mode of the excitation source. Here we propose a new approach, which exploits temperature dependent host sensitized emission from Nd³⁺ and Yb³⁺ lanthanide ions in a YVO₄ matrix. We found out that the emission ratio of these two activators strongly depends on temperature, the size of the nanocrystals and the relative dopant concentration. The novelty comes from the fact that CT → Nd³⁺ and CT → Yb³⁺ are temperature dependent, and therefore helps to double the relative temperature sensitivity from ∼0.12% K⁻¹ up to 0.25% K⁻¹ for the smallest nanocrystals. Based on the temperature dependent luminescence lifetimes of Nd³⁺ and Yb³⁺ activators, we also found out that Nd³⁺ → Yb³⁺ ET has 70–75% efficiency and is temperature dependent.