Lanthanide-dependent photoluminescence and thin film fabrication of host CaWO ₄ micro-materials for potential indoor plant growth applications

A set of scheelite (CaWO₄, <b>CWO</b>) doped samples with formula Ca_1-2<i>x</i>Ln_<i>x</i>Na_<i>x</i>WO₄ (<i>x</i> = 0 and 0.1; Ln = Eu, Tb and Gd) (<b>Eu@CWO</b>, <b>Tb@CWO</b> and <b>Gd@CWO</b>) and doped phases with combinations Ln_<i>x</i>Ln'_<i>y</i> = Eu_0.05Tb_0.05, Eu_0.05Gd_0.05, Tb_0.05Gd_0.05 (<b>Eu,Tb@CWO</b>, <b>Eu,Gd@CWO</b> and <b>Tb,Gd@CWO</b>) and Eu_0.033Tb_0.033Gd_0.033 (<b>Eu,Tb,Gd@CWO</b>) were prepared by a modified four-step sol-gel method followed by calcination at mild temperatures. The solids were characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). An in-depth analysis of the structure and the impact of the synthesis approach on crystallite shape and size was carried out using Rietveld refinements. Besides, the solid-state photoluminescence was studied in terms of excitation, emission 4f-4f* transitions, lifetimes (<i>τ</i>_obs), radiative and non-radiative constants (<i>k</i>_r and <i>k</i>_nrad), energy transfer migration analysis and europium quantum yields. Finally, the Eu-containing CWO samples were selected as a potential emitter device constructed using a spin-coating technique giving rise to homogeneous coatings onto square glass substrates. These results are promising for the design and construction of devices based on wolframate micro-sized materials with emission properties and potential applications in plant cultivation LEDs, sensing, photocatalysis and solar cells.