Effect of structure and composition on optical properties of Er-Sc silicates prepared from multi-nanolayer films

Polycrystalline Er-Sc silicates (Er_xSc_2-xSiO₅ and Er_xSc_2-xSi₂O₇) were fabricated using multilayer nanostructured films of Er₂O₃/SiO₂/Sc₂O₃ deposited on SiO₂/Si substrates by RF-sputtering and thermal annealing at high temperature. RBS, TEM, GIXD, and PL results show the presence of Er_xSc_2-xSiO₅ with an emission peak at 1528 nm for annealing from 900 to 1100 °C, and Er_xSc_2-xSi₂O₇ with an emission peak at 1537 nm for higher annealing temperature. The PL intensity of the Er_xSc_2-xSi₂O₇ phase is five times stronger than that of the Er_xSc_2-xSiO₅ phase at 1250 °C. From PLE and PL spectra of Er_xSc_2-xSi₂O₇ thin film, we schematically illustrate the Er³⁺ Stark energy levels of 4I_13/2 to 4I_15/2 manifolds due to the crystal field strength effect of Sc³⁺. Temperature-dependent PL of the Er_xSc_2-xSi₂O₇ phase exhibits a variation of the full-width at half-maximum (FWHM) from 1.1 to 2.3 nm. The narrow FWHM is due to the small ionic radii of Sc³⁺, which enhance the crystal field strength affecting the optical properties of Er³⁺ ions located at the well-defined lattice sites of Sc silicate. A large excitation cross-section (δ_ex) is equal to 3.0x10^-20 cm² at λ_ex = 1527.6 nm.