Abstract
The combustion synthesis (CS) method was used to synthesize all samples. Y2O3 was our host material. This material was first single doped with Eu3+ and Er3+ ions then co-doped with Yb3+ ions. The concentration of the activator ions Eu3+ and Er3+ were maintained at 1 mol% while that of the sensitizer ion (Yb3+) was varied from 1 mol% to 5 mol%. Anionic group systems (BO33-, PO43-, and SO42-) were incorporated on single doped and co-doped materials. All samples were annealed in an air environment in a tube furnace at 1100 oC for 4 hours.
Samples were characterized via several techniques. X-ray diffraction (XRD) was used to determine phase information, crystal texture, average grain size, lattice strain, and the degree of crystallinity of the prepared phosphor materials. Scanning Electron Microscopy with Energy Dispersion Spectroscopy (SEM-EDS) measurements were used to investigate the surface topography and chemical composition of the phosphor materials. SEM and Energy Dispersion Spectroscopy were used to determine the elemental composition (EDS) and chemical characterization of the phosphor materials. Fourier Transform Infrared (FT-IR) spectroscopy was used to identify the stretching/bending mode frequencies for different structural groups present in the materials. Additionally, X-ray Photoelectron Spectroscopy was used to investigate the surface elemental composition, chemical or electronic state of each element on the sample surface. Ultraviolet-visible-near infrared (UV-Vis) optical spectroscopy was used to analyse the absorption properties of the phosphors. The energy band gap values were estimated from the UV-Vis spectra using Tauc plots.
The XRD results confirmed that our materials crystallized into cubic, tetragonal, and hexagonal structures of Y2O3. This was consistent with the standard JCPDS crystallographic database. The introduction of BO33- and PO43- anionic groups altered the cubic structure of the Y2O3 phosphor material. Using the Scherrerβs equation, the crystallite sizes of the materials were calculated. SEM results showed that our powders were made up of irregular particles with different shapes and sizes with agglomerated formations. The EDS analysis confirmed the presence of all the constituent elements from which our materials were made. FTIR data identified the
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presence of O-H, H-O-H, C-O and Y-O residuals in our samples. XPS confirmed various oxidation states and binding energies in our samples.
Down-conversion and up-conversion emission schemes were successfully investigated through PL measurements. The effect of adding anions on luminescent efficiency was observed in some phosphors. The effect of dopant concentrations proved that it may enhance PL emissions in some cases. It was found that Y2O3-BO3:Eu3+ produces the best red colour emission. Our results, as confirmed by CIE colour coordinates and CCT values suggest that the Y2O3:Er3+, Y2O3-PO4:Er3+, and Y2O3-SO4:Er3+ phosphor materials are potential candidates for green-emitting phosphors. The PL properties of the Y2O3:Eu3+/Yb3+ series at different Yb3+ ion concentrations (1 mol% - 5 mol%) were compared with the anionic-group-incorporated Y2O3:Eu3+/Yb3+ materials, also at different Yb3+ ion concentrations (1 mol% - 5 mol%). In all samples the concentration of Eu3+ ion was kept fixed at 1 mol%. All samples exhibited a prominent UC red emission corresponding to the 5D0 β 7F3 transition. Furthermore, our results, as confirmed by CIE colour coordinates and CCT values suggest that Y2O3:1%Er3+/2%Yb3+, Y2O3-SO4: 1%Er3+/2%Yb3+, and Y2O3-SO4: 1%Er3+/3%Yb3+ nanophosphors produce purest green colours.
KEYWORDS: Combustion, Characterization, Down-conversion, Up-conversion.