Lanthanide-dependent photoluminescence and thin film fabrication of host CaWO4 micro-materials for potential indoor plant growth applications

Abstract

A set of scheelite (CaWO₄, CWO) doped samples with formula Ca_1−2xLn_xNa_xWO₄ (x = 0 and 0.1; Ln = Eu, Tb and Gd) (Eu@CWO, Tb@CWO and Gd@CWO) and doped phases with combinations Ln_xLn′_y = Eu_0.05Tb_0.05, Eu_0.05Gd_0.05, Tb_0.05Gd_0.05 (Eu,Tb@CWO, Eu,Gd@CWO and Tb,Gd@CWO) and Eu_0.033Tb_0.033Gd_0.033 (Eu,Tb,Gd@CWO) 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 (τ_obs), radiative and non-radiative constants (k_r and k_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.