Development of Nd (III)-Based Terahertz Absorbers Revealing Temperature Dependent Near-Infrared Luminescence

• Published in: International journal of molecular sciences Vol. 23; no. 11; p. 6051
• Main Authors: Kumar, Kunal, Stefanczyk, Olaf, Nakabayashi, Koji, Mineo, Yuuki, Ohkoshi, Shin-ichi
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 27.05.2022; MDPI
• Subjects: Crystal structure; Ethanol; Ligands; Luminescence; Medical research; Nitrogen; Single crystals; Spectrum analysis; Spectrum Analysis, Raman; Temperature; Terahertz Spectroscopy; Vibration; ab initio calculation; optical properties; luminescence; ratiometric thermometer; sub-terahertz Raman; terahertz time-domain spectroscopy
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms23116051

Molecular vibrations in the solid-state, detectable in the terahertz (THz) region, are the subject of research to further develop THz technologies. To observe such vibrations in terahertz time-domain spectroscopy (THz-TDS) and low-frequency (LF) Raman spectroscopy, two supramolecular assemblies with the formula [NdIII (phen)3 (NCX)3] 0.3EtOH (X = S, 1-S; Se, 1-Se) were designed and prepared. Both compounds show several THz-TDS and LF-Raman peaks in the sub-THz range, with the lowest frequencies of 0.65 and 0.59 THz for 1-S and 1-Se, and 0.75 and 0.61 THz for 1-S and 1-Se, respectively. The peak redshift was observed due to the substitution of SCN− by SeCN−. Additionally, temperature-dependent TDS-THz studies showed a thermal blueshift phenomenon, as the peak position shifted to 0.68 THz for 1-S and 0.62 THz for 1-Se at 10 K. Based on ab initio calculations, sub-THz vibrations were ascribed to the swaying of the three thiocyanate/selenocyanate. Moreover, both samples exhibited near-infrared (NIR) emission from Nd (III), and very good thermometric properties in the 300–150 K range, comparable to neodymium (III) oxide-based thermometers and higher than previously reported complexes. Moreover, the temperature dependence of fluorescence and THz spectroscopy analysis showed that the reduction in anharmonic thermal vibrations leads to a significant increase in the intensity and a reduction in the width of the emission and LF absorption peaks. These studies provide the basis for developing new routes to adjust the LF vibrational absorption.