Lanthanide-doped Y3Ga5O12 garnets for nanoheating and nanothermometry in the first biological window

Absorption and luminescence spectra in the first biological window of Nd3+ single-doped and Er3+-Yb3+ co-doped Y3Ga5O12 nano-garnets have been studied to evaluate their potential use as simultaneous optical nanoheaters and nanothermometers in biomedicine. Nd3+-doped nano-garnets uses the 808 nm laser radiation, resonant with the largest absorption peak of the 4I9/2 → 4F5/2 transition, for both heating the nanoparticle and populating the 4F3/2 emitting level. Changes in the relative intensities of different emission peaks between Stark levels of the 4F3/2 (R1,2)→4I9/2 (Z1-5) transition can be directly related to the temperature of the nano-garnet. On the other hand, the Yb3+/Er3+combination takes advantage of the large absorption cross-section of the Yb3+ ions at around 920 nm to heat the sample, while triggering the Yb3+-to-Er3+ upconversion energy transfer processes that populate the thermally coupled 2H11/2,4S3/2 emitting levels of Er3+ ions, whose relative intensity changes with temperature can be calibrated. Accurate spatially- and temperature-controlled optically stimulated heating of these nano-garnets from room temperature up to 75 °C within the first biological windows is proved.