Structural and optical characterization of Er-doped CaMoO₄ down-converting phosphors

xEr₂O₃–(1−x)CaMoO₄ (x = 1, 3, 5, 7 and 10 mol%) nanoparticles were synthesized by solid-state sintering at 800°C. X-ray diffraction studies confirmed the tetragonal crystal structure of CaMoO₄, while the doped samples show the co-existence of cubic Er₂O₃ and tetragonal CaMoO₄ and rule out the replacement of Ca²⁺ by Er³⁺ in the structure. The crystal unit-cell dimensions, phase concentration and atomic position coordinates were determined by Rietveld refinement. The short-range structure of CaMoO₄ consists of tetrahedral MoO₄ and snub disphenoid deltahedral CaO₈ units, while the unit cell of Er₂O₃ consists of two types of ErO₆ octahedral units. All MoO₄ units contain Mo—O bonds of equal lengths, whereas two types of slightly different Ca—O bond lengths exist in CaO₈. Raman spectra of the doped samples show only Mo—O vibrational modes and the Raman peaks of Er₂O₃ are masked by Mo—O bond vibrations. CaMoO₄ shows bluish-green emission at 500 nm, while Er-doped samples show strong green emission under UV excitation. UV irradiation (380 nm) induces down-conversion green emission at 531 nm and 552 nm and good color purity in 1 mol% Er₂O₃–CaMoO₄ sample which makes it a potential candidate for applications in optical devices.