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

Abstract

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 SrTiO 3 :Ni 2+ ,Er 3+ nanocrystals, which is the first reported study of nanothermometry based on Ni 2+ ion luminescence. The SrTiO 3 :Ni 2+ ,Er 3+ 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 Ni 2+ ions in the SrTiO 3 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 Ni 2+ band, the spectral shift of its maximum, and the luminescence intensity ratio of Ni 2+ to Er 3+ ions. The temperature-sensing properties of SrTiO 3 :Ni 2+ ,Er 3+ were investigated as a function of Er 3+ concentration. It was revealed that the increase of thermal sensitivity was associated with the decrease of Er 3+ concentration. The highest value of the relative sensitivity, in the physiological temperature range, was obtained for SrTiO 3 :0.05% Ni 2+ ,0.1% Er 3+ nanocrystals, namely, 0.80%/ °C at 40 °C.

LiAl5O8:Fe3+ and LiAl5O8:Fe3+, Nd3+ as a New Luminescent Nanothermometer Operating in 1st Biological Optical Window

“…Several approaches have focused on the enhancement of the relative sensitivity of luminescent thermometers, which includes the optimization of the stoichiometry of the host material as well as the appropriate selection of the optically active ions. A current approach that is being investigated intensively relies on the utilization of the strong temperature dependent luminescence intensity of transition metal ions (TM) in comparison to the luminescence of the lanthanide ions (Ln 3+ ) [9][10][11][12]. This is attributed to the considerable difference in their electronic configuration and interactions with the surrounding ligands; thus the spectroscopic features of the TM and Ln 3+ ions differ.…”

Synergy between NIR luminescence and thermal emission toward highly sensitive NIR operating emissive thermometry

“…Due to low scattering and absorption of the light by the tissue, near infrared (NIR) spectral range, where optical transparency windows of tissues occur, is especially desirable to report temperature dependent spectral signatures. Up to date many different phosphors have been proposed as NIR emitting noncontact temperature sensors including: quantum dots [17][18][19] , silicon nanoparticles 20 , nanogels 21 , inorganic nanoparticles doped with lanthanide ions [22][23][24][25][26][27][28] or transition metal ions [29][30][31][32][33][34] , nanodiamonds 35 , metal-organic frameworks 36 , coordination polymers 37 , semiconductor nanoparticles 38 etc. The progress in luminescence based thermometry, is strongly related to the advancement in available materials, especially because low intensity NIR emission of the phosphors inevitably increases the uncertainty of the temperature determination.…”

Synthesis, Cytotoxicity Assessment and Optical Properties Characterization of Colloidal GdPO4:Mn2+, Eu3+ for High Sensitivity Luminescent Nanothermometers Operating in the Physiological Temperature Range

“…In the case of biological applications, LT needs to reveal high sensitivity to temperature changes in the physiological temperature range (20-50 • C). Moreover, in order to enhance the accuracy and reliability of temperature sensing by the minimization of the light scattering and absorption by the tissue, emission of such phosphors should spectrally fall into biological optical windows (BWs) (BW-I: 650-950 nm, BW-II: 1000-1350 nm, and BW-III: 1500-1800 nm) [15][16][17][18][19][20][21]. Therefore, many potential non-invasive nanothermometers such as YAG garnets [22], NaYF 4 fluorides [23], Au NPs [24], etc., doped with optical active ions operating in the range of BWs have been studied in the last few years.…”

“…Moreover, activation energy, in the case of TM, can be easily modified by the stoichiometry of the phosphor. So far, the use of thermometers based on the emission of transition metals such as Cr 3+ , V 3+,4+,5+ , Ti 3+,4+ , Co 2+ , Ni 2+ , and Mn 3+,4+ has been reported in the literature [17,19,[30][31][32][33]. Another interesting dopant is Mn and specifically Mn 2+ ions.…”