White Light Emission from Thin-Film Samples of ZnO Nanocrystals, Eu(3+) and Tb(3+) Ions Embedded in an SiO(2) Matrix

In this work, a method was developed to determine the concentration of Eu(3+) and Tb(3+) ions in a thin-film sample of SiO(2), co-doped with ZnO-nanocrystals (ZnO-nc), to produce a sample of any desired colour in the International Commission on Illumination (CIE) colour space. Using this method, a white light emitting sample was fabricated. The thin-film sample combines red, green and blue emissions from the Eu(3+) ions, Tb(3+) ions and ZnO-nc, respectively, to create white light or light of any desired colour. The emissions at 614 nm and 545 nm from Eu(3+) and Tb(3+) ions, respectively, is due to the energy transfer from the excited ZnO-nc to the rare-earth (RE) ions. In this way, only a single excitation wavelength is needed to excite the ZnO-nc, Eu(3+) and Tb(3+) ions in the sample to produce emission of a desired colour from the sample. We developed an empirical 4th-degree polynomial equation to determine the concentrations of Eu(3+) and Tb(3+) ions to produce light of any desired colour in the CIE colour space. Based on the above empirical equation, the concentration of Eu(3+) and Tb(3+) ions for a white light emitting sample was found to be 0.012 and 0.024 molar fractions, respectively. The white light emission from the sample was confirmed by fabricating the sample using the low-cost sol–gel process. The stimulated emission spectra and the experimental emission spectra of the white light sample fit very well. The results presented in this work are important to develop energy efficient solid state lighting devices.