The effect of crosslinker contents on the up-conversion luminescence properties of CdNb₂O₆: Er³⁺ powders embedded in the polyethylmethacrylate (PEMA) networks

In this work, CdNb₂O₆:Er₂O₃(1.5 mol% Er³⁺) powders doped with Er³⁺ were embedded in bulk linear polyethylmethacrylate (PEMA) and also as a novelty embedded in bulk PEMA crosslinked networks (gels) with four different crosslinker contents by free-radical crosslinking polymerization with 0.1 EMA (weight %) at 60 °C. The Er³⁺ ions structures embedded in bulk linear PEMA and PEMA gels were investigated by the X-ray diffraction (XRD) technique. The crystalline particle size was found using Pielazsek particle distribution and the Scherrer equation. The average of the crystalline particle sizes was found to be decreasing from 75 nm to 12.50 nm by increasing the crosslinker contents therefore, it was shown that the distribution became more uniform. The morphology of CdNb₂O₆: Er³⁺ embedded in PEMA gel samples was monitored by scanning electron microscopy (SEM). The functional groups on linear PEMA and PEMA gels samples were monitored by Fourier transform infrared (FT-IR) spectra, and the results were consistent with XRD results. The optical properties of polymer samples were investigated by measuring luminescence spectra at room temperature. The doped Er³⁺ ion excited with a 975 nm diode laser achieved the up-conversion (UC) emissions by involving two or three-photon absorptions in the visible region. The effects of crosslinker contents on the UC emission, color tuning, and color quality parameters were observed. As the crosslinker contents increased, the UC emission intensities increased due to increasing the distance between Er³⁺- Er³⁺ ions. The change in color coordinates was also observed by increasing crosslinker content. The chromaticity diagram over the increasing power of the excitation source visualized the tunability of the emitted color. The improvement of the color purity was observed as a function of crosslinker concentration.