Abstract
M.Sc. (Nanoscience)
In this study, solid state method were used to synthesize calcium molybdate doped with Eu3+ ion and anionic groups (BO33-, PO43- and SO42-) for application in white light emitting diodes (LEDs) (solid state lighting) and display. Several sets of phosphor powder materials were prepared, namely CaMoO4:xEu3+, CaMoO4-BO3:xEu3+, CaMoO4-PO4:xEu3+ and CaMoO4-SO4:xEu3+ with various molar concentrations (0.5, 1.0, 1.5, 2.0 and 2.5 mol %). X-Ray diffraction (XRD) was used to identify the phase of the crystals, and subsequently to determine the average size of the phosphors and the degree of crystallinity. Scanning Electron Microscopy (SEM) was used to study the surface morphology (sizes and shapes) of the phosphors and elemental mapping. Elemental composition was determined using SEM and Energy Dispersion Spectroscopy (EDS). Fourier Transformation Infrared (FT-IR) was used for structural elucidation by identifying the stretching/bending mode frequencies. Lastly, surface states of the synthesised materials were studied using X-ray Photoelectron Spectroscopy. The diffuse reflectance and absorption edges were analysed using UV-Vis absorption spectroscopy. Photoluminescence (PL) was used to study the luminescence properties of the phosphor materials. The CaMoO4:xEu3+, CaMoO4-BO3:xEu3+, CaMoO4-PO4:xEu3+ and CaMoO4-SO4:xEu3+ XRD results indicated that the substitution of anions (BO33-,PO43-and SO42-) and Eu3+ dopant ions did not affect the crystal structure of the CaMoO4 phosphors, but greatly influenced the PL intensities of the CaMoO4:Eu3+ phosphors. According to Williamson-Hall equation, the crystallite sizes were ranging from 62 to 72 nm for CaMoO4-SO4:Eu3+phosphors, while for CaMoO4:Eu3+, CaMoO4-BO3:Eu3+ and CaMoO4-PO4:Eu3+ phosphors were ranging from 47 to 48 nm. The SEM images showed that the phosphors were made up of an agglomeration of irregular shaped particles. The luminescence spectra, excited at 395 nm using a monochromatized xenon lamp, for the four different anionic groups (BO33-, PO43- and SO42-) based CaMoO4:Eu3+ phosphors were recorded. The photoluminescent (PL) spectra showed an intense red emission at 615 nm belonging to the 5D0→7F2 electric dipole transition while the 5D0→7F1 was accountable to magnetic dipole. The highest PL intensity was observed for the CaMoO4-SO4:Eu3+ phosphor material. The calculated CIE (Commission Internationale de l’Eclairage) confirmed that the emission colour was lying in the red or orange region and the CIE coordinates changed from yellow to red, orange-red by varying the molar concentration of Eu3+ ion in CaMoO4-SO4:Eu3+ phosphors, while CaMoO4:Eu3+, CaMoO4-BO3:Eu3+ and CaMoO4-PO4:Eu3+ phosphors are stable at red region. The PL data suggested that our materials have potential applications as source of red light in red light emitting diodes.