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Transition Metal Ion-Based Nanocrystalline Luminescent Thermometry in SrTiO3:Ni2+,Er3+ Nanocrystals Operating in the Second Optical Window of Biological Tissues

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journal contribution
posted on 17.07.2019, 17:41 by C. Matuszewska, K. Elzbieciak-Piecka, L. Marciniak
Luminescence thermometry in the second and third optical windows of biological tissues has gained importance in recent years due to the reduction of both absorption and scattering effects in human tissues, which substantially increase its applicative potential. In this work, we present a luminescent thermometer based on SrTiO3:Ni2+,Er3+ nanocrystals, which is the first reported study of nanothermometry based on Ni2+ ion luminescence. The SrTiO3:Ni2+,Er3+ nanocrystals were successfully synthesized using the Pechini method. The spectroscopic properties of obtained nanocrystals were investigated in a wide temperature range, namely, between −150 and 210 °C. It was found that Ni2+ ions in the SrTiO3 matrix are characterized by broadband emission localized in the II optical window at about 1200 nm, which additionally changes its spectral position toward longer wavelengths with the rise of temperature. Three temperature-dependent parameters were studied for luminescence thermometry: changes in the emission intensity of the Ni2+ band, the spectral shift of its maximum, and the luminescence intensity ratio of Ni2+ to Er3+ ions. The temperature-sensing properties of SrTiO3:Ni2+,Er3+ were investigated as a function of Er3+ concentration. It was revealed that the increase of thermal sensitivity was associated with the decrease of Er3+ concentration. The highest value of the relative sensitivity, in the physiological temperature range, was obtained for SrTiO3:0.05% Ni2+,0.1% Er3+ nanocrystals, namely, 0.80%/°C at 40 °C.