Evaporation of levitating microdroplets containing nanoparticles: luminescent Gd2O3:Er3+, TiO2, polystyrene; illumination with 806 nm laser from below

Description

Microdroplets of suspension were levitated in a linear quadrupole trap and studied similarly as described e.g. in Y. Shopa et al., JQSRT 296 (2023), but illumination with an 806 nm diode laser (CW, ~1.5 W), which excited luminescence by up-conversion, was provided (vertically) from below. In 2023, its polarization was s+p (~45deg) and from the beginning of 2024, it was p. In some experiments, the droplet was additionally illuminated with a 512 nm diode laser with p polarisation. The suspended phase consisted of nanoparticles of Gd2O3:Er3+ of several concentrations, and for comparison, polystyrene of 1 micrometer diameter and TiO2 of 100 nm diameter. The continuous phase consisted of diethylene (2EG), triethylene (3EG), and tetraethylene (4EG) glycols. The data is divided into the folders correspondingly. Two groups of spectral lines were (usually) visible (green (stronger) and red). We followed the temporal evolution of several selected lines, both in luminescence and in scattering at right angle (usually 538, 548, 553, 562, 633, 654, 661, 675, 682, 783, 806 nm): files *-Spectra.csv, where * (in hh_mm_ss format) always denotes the time of measurement file creation. Simultaneously the shadow image of the droplet was recorded (non-coherent light, 633 nm LED) - in some cases, a movie: *_Shadow-*.avi is provided. The droplet radius was measured by fitting an ellipse to the shadow edge. The ellipse parameters temporal evolution are stored in *-Shadow.pdf files: time, mean diameter (mean of the ellipse axes), long axis rotation, X and Y of the centre, long and short axis, border length, X and Y of “the centre of mass” of the border, fitting error. The microdroplet's vertical position was stabilised with a DC field. The corresponding voltage variation and other stabilisation system parameters are stored in *.csv files: KeyStab: 0 – stabilisation off, 2 – on, k_PID – proportionality parameter of the software voltage regulator, freq – trapping AC field frequency. In some cases, partially concurrently light was collected at a right angle with a PMT for the green 512 or 806 nm laser. The photon count rate is stored in *-CRM.csv files. Time stored in corresponding files was synchronised. In-focus movies (see readme.txt for details) of the evaporating microdroplet were recorded for certain experiments to illustrate its evolution – no synchronisation is available. It must be kept in mind that the observed image is for the most part laser speckle. The "Laser on/off" pertains to the 806 nm laser. Further details can be found in the readme.txt files in the corresponding folder. (No)_th_spectrum.csv represents the ith recorded spectrum from the corresponding experiment. The parameters of the Gd2O3:Er3+ samples can be found in the .pptx files.

Institutions

Categories

Funding

Licence