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In this work we present the spectroscopic properties of LaGaO3:V,Nd3+ nanocrystals, which have been successfully obtained by the Pechini method. This is the first study where vanadium ions were applied in a LaGaO3 lattice for a non-contact luminescent thermometer. It was found that vanadium ions in the LaGaO3 matrix appear in three oxidation states, namely V5+, V4+ and V3+. It was found that the relative emission intensities of various states of vanadium ions depend strongly on grain size and therefore the emission color of LaGaO3:V can be easily modulated via the annealing temperature. The spectroscopic properties of this material were investigated in a wide temperature range (-150-300 °C). It was found that in the case of V-singly doped nanocrystals, the V4+ ions, reveal the best temperature sensing performance with high relative sensitivity (S = 1.76% °C-1) and broad usable temperature range (-50-150 °C). The different rates of thermal luminescence quenching of the vanadium ions provide three forms of non-contact temperature sensor, namely LaGaO3:V5+,Nd3+, LaGaO3:V4+,Nd3+ and LaGaO3:V3+,Nd3+. The highest sensitivities were found to be 1% °C-1 (at -5 °C and 90 °C), 0.49% °C-1 (at -20 °C) and 1.44% °C-1 (at 75 °C) for LaGaO3:V5+,Nd3+, LaGaO3:V4+,Nd3+ and LaGaO3:V3+,Nd3+, respectively.

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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 Smax 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 Smax = 0.56%/°C at −80 °C, upon separate excitation of Fe3+ and Nd3+ ions using 266 nm and 808 nm light, respectively.

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.

The relative sensitivity and usable temperature range of Fe3+,Cr3+-based luminescent thermometers can be tuned by modification of the crystal field strength.

In this work the influence of the Ga3+ concentration on the luminescent properties and the abilities of the Y3Al5−xGaxO12: V nanocrystals to noncontact temperature sensing were investigated. It was shown that the increase of the Ga3+ amount enables enhancement of V4+ emission intensity in respect to the V3+ and V5+ and thus modify the color of emission. The introduction of Ga3+ ions provides the appearance of the crystallographic sites, suitable for V4+ occupation. Consequently, the increase of V4+ amount facilitates V5+ → V4+ interionic energy transfer throughout the shortening of the distance between interacting ions. The opposite thermal dependence of V4+ and V5+ emission intensities enables to create the bandshape luminescent thermometr of the highest relative sensitivity of V-based luminescent thermometers reported up to date (Smax, 2.64%/°C, for Y3Al2Ga3O12 at 0 °C). An approach of tuning the performance of Y3Al5−xGaxO12: V nanocrystals to luminescent temperature sensing, including the spectral response, maximal relative sensitivity and usable temperature range, by the Ga3+ doping was presented and discussed.