Structural and Luminescence Properties of Eu-Doped PMO Films with Ethylene Bridge and Methyl Terminal Groups

Abstract

Eu-doped periodic mesoporous organosilicate (PMO) films with terminal methyl and ethylene bridging groups have been synthesized using sol-gel technology and spin-coating, employing evaporation-induced self-assembly (EISA), on silicon wafers. Eu doping is achieved by the dissolution of Eu(NO3)3·6H2O in the precursor solution. The deposited films are characterized using Fourier transform infrared (FTIR) spectroscopy, ellipsometric porosimetry (EP), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy. It is observed that Eu doping reduces the concentration of terminal methyl groups, makes the films more hydrophilic and reduces the pore size and open porosity. The reduction reaction Eu3+ → Eu2+ occurs in the pores of organosilicate glass (OSG) films, which was confirmed by the depth profiling XPS. Eu3+ was still present on the top surface of the films. The presence of Eu3+ and Eu2+ gives luminescence emission in the range of 600–630 nm (Eu3+) and 290–400 nm (Eu2+). The Eu2+/Eu3+ concentrations ratio depends on CH3 groups concentration in the films. The concentration of Eu2+ ions in the pores can be reduced by exposure to inductively coupled (ICP) oxygen plasma. The observed shift in the luminescence spectra towards the UV region, in comparison to previously reported Eu-doped organosilicate films, can be attributed to the energy transfer occurring between the host material and Eu2+ ions.