Light Science & Applications: Methods for measuring the photothermal conversion efficiency of solid materials

The Beijing Key Laboratory of Nano-photonics and Ultra-Precision Optoelectronic Systems, Beijing Institute of Technology, studied the method of measuring the photothermal conversion efficiency of solid materials. the findings are published in Light: A general methodology to measure the light-to-Heat conversion efficiency of solid materials. Science & Applications.

Photothermal conversion has been extensively studied due to potential applications such as photothermal therapy and solar energy harvesting. As a basic property of materials, the accurate measurement of photothermal conversion efficiency (LHCE) is very important for the development of advanced photothermal materials. A photothermal and electrothermal equivalent (PEE) method is reported to measure the LHCE of solid materials by simulating laser heating processes and electric heating processes. The temperature variation of the sample during electric heating was first measured, allowing us to derive the heat dissipation coefficient by linear fitting at the heat equilibrium. The LHCE of the sample under laser heating can be calculated if the heat dissipation factor is taken into account. Combined with theoretical analysis and experimental measurement, the validity of the hypothesis is further discussed. The error obtained is less than 5%, and the reproducibility is good. The method has universality for the measurement of LHCE of inorganic nanocrystals, carbon-based materials and organic materials, indicating the applicability of the method to a variety of materials.

Figure 1 briefly describes the experimental measurements and data analysis of the PEE method. Electrothermic measurement is done by determining the temperature rise of the sample on the resistor using a thermal imager (TGC). Similarly, photothermal measurements are done by measuring the temperature rise of a sample under laser heating. Maximum temperature change can be obtained by TGC monitoring average temperature (FIG. 1c) by plotting temperature change curves over time (FIG. 1a, b). By linear fitting of maximum temperature change and electric heating input power curve, the heat dissipation coefficient of the sample can be obtained (Figure 1d). The LHCE of the sample is calculated by the heat balance equation of laser heating considering the light absorption coefficient and heat dissipation coefficient.

Figure 1: Schematic diagram of PEE method
The LHCE of Au nanorods, PbSe and Cu2Se nanocrystals was measured by PEE method. Transmission electron microscopy (TEM) of gold nanorods is shown in Figure 2a.

Figure 2: LHCE calculation of Au nanorods, PbSe nanocrystals and Cu2Se nanocrystals.
To demonstrate the suitability of the PEE method, we also measured the LHCE of carbon-based materials and polymers, including multi-walled carbon nanotube dispersions (MWCN)(Figure 3a-d), graphene sols (GO), graphene dispersions, and polyaniline (PANI)(Figure 3e-h). The results show that no phase transition occurs during the heating process.

Figure 3: LHCE calculation of MWCN and PANI.
To analyze the error and statistical distribution of the PEE method, temperature changes of MWCN(FIG. 4a), PbSe, and Au nanorods were recorded during 10 tests under continuous laser heating.

Figure 4: LHCE of all samples.
The model hypothesis analysis, in order to elucidate the effect of thermal radiation from the side of the resistor in the hypothesis, changed the size of the test area to alternate heat radiation to the sample.

Figure 5: Analysis of model assumptions

Links to relevant papers:
https://www.nature.com/articles/s41377-023-01167-6

Source: Sohu-Yangtze River Delta laser Alliance