Raman scattering and luminescence in single crystals of the amino acid glycine C₂H₅NO₂ with an admixture of croconic acid C₅H₂O₅

Abstract

Single crystals of the amino acid glycine (Gly) C2H5NO2 doped with croconic acid (CA) C5H2O5 were synthesized by evaporation from an aqueous solution. The crystals grow in the form of hexagonal pyramids or thin plates. Analysis of polarized Raman scattering spectra (excitation wavelength of 532 nm) measured at room temperatures showed that crystals in the form of pyramids corresponded to γ-polymorph (γ-Gly), and crystals in the form of plates to α-polymorph of glycine (α - Gly). The presence of croconic acid molecules in the crystals is confirmed by the change in their color from white in pure Gly crystals to light or dark yellow, characteristic of CA crystals, as well as the presence of weak lines corresponding to CA in the Raman spectra. In single crystals of both Gly:CA polymorphs, strong green luminescence significantly exceeding the intensity of Raman scattering is observed in the range 400 - 700 nm with a maximum at 510 nm (2.44 eV) upon excitation at λ= 325 nm.

Croconic Acid Doped Glycine Single Crystals: Growth, Crystal Structure, UV-Vis, FTIR, Raman and Photoluminescence Spectroscopy

“…It has been established that γ-Gly forms pyramidal crystals, while α-Gly forms plate-like crystals. The incorporation of CA molecules in a glycine crystal does not noticeably change the spectral positions of Raman lines in the high-energy region of the spectrum (2900-3100 cm −1 ), but leads to modest shift of several low-energy lines, which characterizes the effect of CA doping on the lattice vibration spectrum [32].…”

“…Generally, the aim of this research was the synthesis of CA-doped αand γ-Gly single crystals and the study of their structural and optical properties. Preliminary results on Raman and photoluminescence spectroscopy were presented in our conference paper [32].…”