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Time-Resolved Temperature-Jump Measurements and Theoretical Simulations of Nanoscale Heat Transfer Using NaYF₄:Yb³⁺:Er³⁺ Upconverting Nanoparticles

Rafiei Miandashti, Ali, Khosravi Khorashad, Larousse, Govorov, Alexander O., Kordesch, Martin E., Richardson, Hugh H.
Journal of physical chemistry 2019 v.123 no.6 pp. 3770-3780
energy balance, finite element analysis, heat transfer, luminescence, nanocrystals, nanoparticles, optical properties, physical chemistry, prediction, simulation models, temperature, thermal conductivity, thermal diffusivity, thermometers
We introduce for the first time a time-resolved temperature measurement technique which relies on temperature-jump luminescence thermometry using NaYF₄:Yb³⁺:Er³⁺ upconverting nanocrystals. This new time-resolved technique is based on optical thermometry using upconverting nanoparticles (UCNPs) and does not have to infer temperature from changes in the optical properties of the heater or surrounding local environment. We have prepared gold-decorated UCNPs that function as a dual single-heater thermometer system. We measure the time-resolved temperature jump from nanocrystal clusters and compare our results to simulated thermal transfer data generated using finite element methods. The simulated data show that temperature dissipation follows a power law where the temperature change is inversely related to time. This result agrees with a thermal diffusion model where a semi-infinite medium is exposed to a sudden temperature change at its surface, but the simulated results do not agree that the heat transfer process can be described by a single thermal diffusivity parameter. In contrast to the thermal diffusion model, our experimental and simulation data show that the heat generation and dissipation process is described by an energy balance model where the thermal conductivity for heat dissipation and heat capacity of the heated object are separated. The experimental data agree with the prediction of the energy balance model where the temperature is expected to increase and decay with time as a single exponential.