Lanthanide Ion-Driven Phase Stabilization in β‑Ca2SiO4 Luminescent Nanomaterials for Light-Emitting Diode Applications.

Lanthanide-doped β-Ca₂SiO₄ has been regarded as a promising material for use in light-emitting diode (LED) phosphors. Nevertheless, the performance of these luminescent materials activated by lanthanide ions depends strongly on the host matrix. The challenge lies in controlling the phase under ambient conditions in a material that exists in five polymorphic forms. Herein, we report the synthesis of β-Ca₂SiO₄ containing Ce and Eu ions via the Sol–Gel method. The pure and doped samples were characterized using thermogravimetric (TG) and differential thermal (DT) analysis, X-ray diffraction (XRD) and Rietveld–XRD analysis, scanning electron microscopy (SEM), X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and defect calculations. XRD analyses show the predominant formation of the β-phase. Morphological analyses by SEM show smaller particle sizes in Ce- and Eu-doped β-Ca₂SiO₄ than pure samples. This result suggests that Ce³⁺ is more efficient at stabilizing the β-Ca₂SiO₄ polymorph. The PL emission of the β-Ca₂SiO₄:Eu, excited at 393 nm, provides evidence about the existence of two nonequivalent sites, with one of them evolving to a high symmetry site and the other one remaining in a low symmetry. PL results are corroborated by defect calculations in which it is evident that both Eu³⁺ and Ce³⁺ ions prefer to be incorporated into the two Ca2 sites compensated by a Ca1 vacancy, including a probable change in the coordination number of the Eu³⁺ ion. The abrupt distortion of one of the Eu³⁺ sites is accompanied by the high ⁵D₀ → ⁷F₄ transition. Also, we present XANES and XPS analyses combined with defect calculations for Eu²⁺ and Ce⁴⁺ ions to discuss the likely coexistence of valency states in the host matrix. Lastly, the results offer insights into improving the performance of phosphor-converted white LEDs. [ABSTRACT FROM AUTHOR]