The influence of host material on NIR II and NIR III emitting Ni2+-based luminescent thermometers in ATiO3: Ni2+ (A = Sr, Ca, Mg, Ba) nanocrystals

In this work we present for the first time the effective modulation of spectroscopic parameters of Ni2+ emission based luminescence nanothermometer (LNT). Emission of Ni2+ ions, highly susceptible to the local symmetry variations, can be easily modulated by the change of the crystal field strength of matrix. In this approach we proposed four ATiO3 perovskite nanocrystalline matrixes, namely SrTiO3, CaTiO3, MgTiO3, BaTiO3, in which the change of the crystal field strength is induced by the Ti4+ - O2− distance elongation. With the increase of this distance we achieved 500 nm spectral shift of Ni2+ emission maximum from 1200 nm for SrTiO3: Ni2+ up to 1700 nm for MgTiO3: Ni2+. Furthermore, it was found that the host material strongly influenced thermal quenching of Ni2+ emission intensity, which had high impact on the value of relative sensitivity (SR). The highest rate of thermal quenching was observed for MgTiO3: Ni2+ nanocrystals with SR>1.4%/K, while in physiological temperature range highest SR was obtained for CaTiO3: Ni2+ (1.4%/K < SR<3.1%/K). Additionally, for two host materials after co-doping with Er3+ ions ratiometric LNTs were accomplished, namely SrTiO3: Ni2+, Er3+ and CaTiO3: Ni2+, Er3+ with the highest obtained SR in physiological temperatures reaching 0.44%/K and 0.37%/K, respectively.