Preparation and characterization of isostructural lanthanide Eu/Gd/Tb metal-organic framework thin films for luminescent applications

Abstract

The preparation of the lanthanide metal-organic frameworks LnMOFs (Ln = Eu, Gd, Tb, Eu0.5Gd0.25Tb0.25, Eu0.25Gd0.5Tb0.25 and Eu0.25Gd0.25Tb0.5) by solvothermal synthesis is reported. Three synthesis routes (A, B, C) using different solution (N,N-dimethylforamide (DMF)/H2O/EtOH (A) and with addition of modulator (sodium acetate) to DMF/H2O (B) or EtOH/H2O (C) are presented. Structural characterizations reveal that the coordination effect between Eu3+, Gd3+, Tb3+ ions and 1,3,5-benzenetricarboxylic acid (BTC) ligand in LnMOFs is confirmed. The advantage of green modulation (C) method is creation of rod-like nanocrystals (~50–150 nm). Transparent LnMOF thin films are prepared by dropping of colloidal solution of LnBTC nanocrystals on SiO2/Si substrates with Pt interlayer. Three new ratios of lanthanides (Eu0.5Gd0.25Tb0.25, Eu0.25Gd0.5Tb0.25 and Eu0.25Gd0.25Tb0.5) in mixed films with bidoped concentration of Eu3+/Tb3+ ions in Gd3+ matrix are select. Comparing luminescence properties of Eu0.25Gd0.5Tb0.25BTC powder and film (C method), film provide the quantum efficiency value 8.6 times lower than powder. Eu0.5Gd0.25Tb0.25BTC film present increase of europium mean lifetime by more than 5 times and improvement for quantum efficiency of about 300%, regarding to Eu0.25Gd0.5Tb0.25BTC film and bicolor emission profile depending only of excitation wavelengths. The resulting transparent luminescent LnMOF films can be used in the fabrication of different optical devices.