Synthesis, optical properties, energy transfer mechanisms, and mechanical characteristics of NaLa(MoO₄)₂: Er³⁺, Nd³⁺...

NaLa(MoO₄)₂ (NLM): Er³⁺, Nd³⁺ phosphors were successfully synthesized by a high-temperature solid-state reaction method, and their phase structure, electronic structure, and near-infrared luminescence properties were systematically investigated. XRD, SEM, and EDS analyses indicate that Er³⁺ and Nd³⁺ ions were effectively incorporated into the NLM host lattice while maintaining a well-defined single-phase structure. Combined with Rietveld refinement and first-principles calculations, the lattice variation, band structure, and density of states of the co-doped system were analyzed. The results reveal that the introduction of rare-earth ions generates localized 4f electronic states near the Fermi level and reduces the band gap, which is favorable for electronic transitions and energy-transfer processes.Based on absorption spectra and Judd-Ofelt theory, the intensity parameters, oscillator strengths, radiative transition probabilities, as well as the absorption and emission cross-sections of Nd³⁺ ions were evaluated. Under 808 nm excitation, the co-doped samples exhibit enhanced 1064 nm near-infrared emission, indicating that Er³⁺ ions can effectively act as sensitizers to promote the luminescence of Nd³⁺ ions. Furthermore, the variations in fluorescence lifetimes at 1550 nm and 1064 nm, together with the calculated energy-transfer efficiency, further confirm the occurrence of the Er³⁺ → Nd³⁺ energy-transfer process. In addition, the upconversion emission of Er³⁺ under 980 nm excitation is significantly suppressed after Nd³⁺ incorporation. Combined with the excitation power-dependent luminescence behavior in the range of 157-507 mW, the upconversion process is identified as a two-photon mechanism.The calculated elastic constants and related mechanical parameters demonstrate that the co-doped NLM system possesses good structural stability and moderate lattice flexibility. Such a stable local crystal-field environment is beneficial for suppressing non-radiative relaxation losses and maintaining efficient near-infrared luminescence and energy transfer. Overall, the obtained results suggest that NLM: Er³⁺, Nd³⁺ phosphors have promising potential for near-infrared luminescence applications.