Thermal, Spectroscopic and Luminescence Properties of Lanthanide/PMMA Hybrid Materials

A new class of Ln(III) Schiff base (SB) complexes has been synthesized with the general formula [LnL(hfac)3], where Ln = Tb (TbL), Eu (EuL), Sm (SmL) or Gd (GdL). The molecular structure of the complex was determined using the X-ray diffraction method. The IR spectra show that the C=O stretching is shifted from 1695 cm−1 in pure PMMA to 1719–1724 cm−1 in LnL-PMMA hybrid materials. This means that LnL materials are successfully embedded into the PMMA backbone in the polymeric films. However, the Ln(III) SB complexes exhibit emission spectra that cover the visible region. The TbL complex displays an intense green emission combined with a large emission lifetime of 0.505 ms. However, the incorporation of Ln-SB complexes into PMMA (polymethylmethacrylate) polymeric films was investigated. The thermal stabilities of the LnL-PMMA hybrid materials increased from 140 to 250 °C when compared with the LnL-SB complexes. Furthermore, their luminescence intensity and lifetimes were also enhanced due to their induced structural rigidity. The molecular interactions of the LnL complexes with the PMMA matrix were monitored by investigating the luminescence properties of EuL-PMMA. Detailed photoluminescence studies showed insights into the non-radiative rates and improved quantum yields (QEu = 23%) from Eu(III). Furthermore, the higher values of Judd–Ofelt parameters Ω2 and Ω4 indicate strong hydrogen bonding interactions between L and PMMA. Nevertheless, these significant optical properties enable LnL-PMMA polymeric materials as colored phosphors for the design of opto-electronic devices.