Evaporation of levitating microdroplets containing luminescent Gd2O3:Er3+ nanoparticles (also with TiO2 nanoparticles)

Description

Microdroplets of suspension were levitated in a linear quadrupole trap and studied as described e.g. in Y. Shopa et al., JQSRT 296 (2023). The suspended phase consisted of nanoparticles of Gd2O3:Er3+ of several sizes and concentrations. In a few experiments, TiO2 nanoparticles of 100 nm diameter were also added. The continuous phase consisted of diethylene (2EG), triethylene (3EG) and tetraethylene (4EG) glycols. Experiments with droplets of suspension of TiO2 nanoparticles only in 4EG were performed for comparison. The data is divided into the folders correspondingly. Up-converted luminescence was excited with an 806 nm diode laser (CW, ~1.5 W). 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). 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 together with 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 (~200 fps) 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 speckle (from the green laser). 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 samples can be found in the .pptx files.

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