Thermally Induced Morphological and Structural Transformations on Eu ²⁺/Eu ³⁺-Coactivated Calcium Silicate Nanophosphors

Abstract

This study presents an approach for synthesizing Eu ²⁺/Eu ³⁺-coactivated Ca ₂SiO ₄ nanophosphors, by adjusting the ratio of both activators within a singular host material. Utilizing a hydrothermal method complemented by a postreduction sintering process, we fabricated a series of phosphors characterized by uniform 30–50 nm spherical nanoparticles. These engineered phosphors manifest multichannel luminescence properties and exhibit simultaneous blue and red emission from Eu ²⁺ and Eu ³⁺, respectively. Meticulous control of the 5% H ₂–95% N ₂ reduction temperature allowed for precise tuning of the Eu ²⁺ and Eu ³⁺ ions within the host lattice, which enabled the strategic adjustment of their luminescent outputs. Utilizing X-ray photoelectron spectroscopy (XPS), we could discern subtle alterations in the europium oxidation state. By using a transmission electron microscope (TEM) and an X-ray diffractometer (XRD), we found that the subsequent changes by reductive sintering to particle size, morphology, and mixed crystal structures influenced the materials’ luminescent characteristics. Our findings herald a significant advancement in solid-state lighting, with the potential for the use of Eu ²⁺/Eu ³⁺-coactivated calcium silicate nanophosphors to develop white light emission technologies endowed with enhanced color rendering and luminous efficacy.