An investigation of the synthesis and properties of nano crystalline Y2O3:Eu3+ (prepared using micelle- based precursors)

Abstract

The work described in this thesis was aimed at understanding the reactions taking place on heating Y2O3:Eu3+ phosphor precursors in the nano particle size regime. Herein combustion syntheses to prepare nanometer sized crystallites of cubic Y2O3:Eu3+ using precursors containing sacrificial long chain alkylammonium cations (the fuel) are reported. Using this method it proved possible to produce cubic Y2O3:Eu3+ crystallites in the 20-70nm size range. The presence of CO2 bands in the infra red spectra of the surface of the cubic Y2O3:Eu3+ crystallites are also reported. These bands are identical in position to those found in [(Y, Eu)OHCO3.H2O], and are explained as arising from the spontaneous reaction of the surface of the nanometer sized particles of cubic Y2O3:Eu3+ with atmospheric CO2 and water vapour. This indicates that nanometer sized particles of cubic Y2O3:Eu3+ are thermodynamically unstable in the atmosphere and must be protected against such back reactions. This could be done with surface coatings. Precursors of the products were prepared from methanolic and ethanolic solutions and then these were fired at temperatures of 650 and 900°C. Products (samples) prepared at a temperature of 900°C were observed to be all white powders in colour. Under 254nm uv excitation the samples prepared at 650°C displayed a weak red luminescence which was in contrast to the strong red luminescence from the samples prepared at 900°C that is characteristic of the Eu3+ ion in cubic Y2O3. The strongest red luminescence comes from 1:3 material sample ratios prepared at 900°C. The understanding of the chemistry behind the reactions and the characterisation and properties of the products formed are the major aims of the work reported here.