LiAl(5)O(8):Fe(3+) and LiAl(5)O(8):Fe(3+), Nd(3+) as a New Luminescent Nanothermometer Operating in 1st Biological Optical Window

New types of contactless luminescence nanothermometers, namely, LiAl(5)O(8):Fe(3+) and LiAl(5)O(8):Fe(3+), Nd(3+) 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 Fe(3+) ions is affected by the change in temperature, which induces quenching of the (4)T(1) ((4)G) → (6)A(1) ((6)S) Fe(3+) 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 LiAl(5)O(8): 0.05% Fe(3+) 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 LiAl(5)O(8):0.5% Fe(3+) to be 0.92% °C at −100 °C and for LiAl(5)O(8):0.01% Fe(3+) to be 0.79% °C at 150 °C. The cytotoxicity assessment carried out on the LiAl(5)O(8):Fe(3+) nanocrystals, demonstrated that they are biocompatible and may be utilized for in vivo temperature sensing. The ratiometric luminescent nanothermometer, LiAl(5)O(8):Fe(3+), Nd(3+), which was used as a reference, possesses an S(max) = 0.56%/°C at −80 °C, upon separate excitation of Fe(3+) and Nd(3+) ions using 266 nm and 808 nm light, respectively.