Lanthanide-Induced Local Structural and Optical Modulation in Low-Temperature Ag2Se

초록

Low-temperature Ag2Se is a narrow-band semiconductor, with its transport and optical properties significantly influenced by the local coordination environment. This study investigates the effects of La and Gd incorporation using DFT+U calculations and Ag-K edge EXAFS analysis. Analysis of electron localization function (ELF) and charge density differences reveals increased electron localization at dopant sites. Additionally, k(3)chi(k) and wavelet transforms demonstrate that the first M-Se shell shifts from approximately 1.346 & Aring; in Ag-Se to around 1.386 & Aring; and 1.291 & Aring; for La-Se and Gd-Se, respectively (phase-uncorrected), thereby confirming dopant-specific lattice distortions while maintaining the orthorhombic framework. The observed changes are associated with an increase in dielectric strength, with epsilon(2) increasing from approximately 30-40 in pristine Ag2Se to around 50-60 for La and 70-80 for Gd at low photon energies, alongside enhanced absorption nearing 1.32-1.34 x 10(5) cm(-1). The characteristic plasmon resonance in the range of 15-20 eV is maintained. Rare-earth substitution effectively adjusts local bonding and low-energy optical response in Ag2Se, with Gd demonstrating the most significant impact among the examined dopants.

키워드