Luminescent analysis of [Eu2DPA3] MOF as high purity red-emitting phosphor with thermal stability

Abstract

In this work, the synthesis of a red-emitting phosphor with thermally stable photoluminescence, [Eu2DPA3]n MOF is reported. Thermogravimetric analysis (TGA) confirmed the formation of the coordination polymer with 2:3 metal to ligand stoichiometry, without water contents. Fourier transform infrared spectroscopy (FTIR) evidenced bands corresponding to different coordination modes between DPA carboxylates and pyridine nitrogen atoms with the Eu3+ ion, among them were COOEu, COOEu2, COOEu3, as well as picolinic mono- and bis-chelates, clearly indicating the formation of a coordination polymer. The luminescent properties were determined using 300 and 395 nm as exciting wavelengths, getting the typical emission bands of Eu3+ (5D0 →7F0,1,2,3,4). Luminescence lifetimes (τ) were determined using a monoexponential fit obtaining values of 2.2 (λexc = 300 nm) and 1.9 ms (λexc = 395 nm). The [Eu2DPA3]n MOF shows quantum efficiency of 48% (λexc = 300 nm) and 42% (λexc = 395 nm), and an absolute quantum yield of 55 and 31% with the same excitation conditions. The photometric study indicates that the luminescent response to excitation with 300 and 395 nm is practically identical, with a high purity red color >98%, and a chromatic coordinate of 0.65, 0.35. The temperature-dependent luminescence properties revealed a stable luminescent signal in the range of 30–150 °C, with a signal loss of 3.5% and an extinction energy (ΔE) of 0.21 eV.