Surface-enhanced Raman scattering and density functional theory study of selected-lanthanide-citrate complexes (lanthanide: Tb, Dy, Ho, Er, Tm, Yb and Lu)

TL;DR

This study combines surface-enhanced Raman scattering and density functional theory to analyze lanthanide-citrate complexes, revealing spectral trends related to lanthanide type and electronic interactions.

Contribution

It introduces an integrated SERS and DFT approach for detailed spectral assignment and trend analysis of multiple lanthanide-citrate complexes.

Findings

Peak intensities vary systematically across lanthanides.

Spectral trends correlate with lanthanide electronic interactions.

DFT simulations support experimental peak assignments.

Abstract

In this study, surface-enhanced Raman scattering (SERS) and density functional theory (DFT) calculations were combined to investigate the SERS spectra of Ln-citrate complexes (Ln: Tb, Dy, Ho, Er, Tm, Yb, and Lu) under 488 and 532 nm excitation. Peak assignment was supported by simulated SERS spectra calculated with an optimized DFT method using large-core effective core potentials. The main bands near 935, 1060, 1315, and 1485 cm-1 were assigned to (C-COO-) + (CH2), (CH2) + (C-O -- Ln), sym(COO-) + (CH2), and asym(COO-) + (CH2), respectively. Relative peak intensities were evaluated by normalizing the bands near 935, 1060, and 1485 cm-1 to that near 1315 cm-1. The ratios I_935/I_1315 and I_1485/I_1315 generally increased from Dy-citrate to Lu-citrate, whereas the I_1060/I_1315 ratio decreased. These trends were observed under both excitation wavelengths. The decrease in relative SERS peak intensity of the 1060 cm-1 band is attributed to stronger Ln-O interaction and reduced polarizability change, whereas the increases of the 935 and 1485 cm-1 bands are likely related to changes in local electronic distribution and effective symmetry sensitivity.