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 nano-heaters and nanothermometers in biomedicine. Nd3+ -doped nano-gamets uses the 808 nm laser radiation, resonant with the largest absorption peak of the I-4(9/2)-> F-4(5/2) transition, for both heating the nanoparticle and populating the F-4(3/2) emitting level. Changes in the relative intensities of different emission peaks between Stark levels of the F-4(3)/2(R-1(,2)) -> I-4(9/2)(Z(1)(.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 H-2(11/2),S-4(3)/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 degrees C within the first biological windows is proved.