ABSTRACT:
Dually excitable nanocrystalline Ba5Zn4Y8O21:Eu3+ phosphor with excellent color domain was developed via urea assisted solution combustion synthesis using metal nitrates as the precursor components. Rietveld refinement technique was implemented to confirm the phase purity and structural framework. It was found to crystallize in a tetragonal lattice with the I4/m(87) space group. The low phonon nature of the host was found responsible for the blue to red color tunability as a function of dopant concentration yielding Ba5Zn4Y6Eu2O21 as the optimum composition for red luminescence. The refractive index of the host and the critical distance for non-radiative energy transfer were calculated to be 2.15 and 8.0474 Å respectively. The refractive index and photoluminescent emission spectra were exploited to calculate Judd-Ofelt intensity parameters. Dipole/Quadruple–Quadruple (Q–Q) interactions were ascribed as the major factor responsible for concentration quenching arising from the over-doping of the activator ions. Ab-initio analysis by density functional theory (DFT) revealed the electronic band structure and the density of states with a band gap of 2.872 eV. The greater band offset for f-f transition and tunable multiphonon relaxation initialized a phenomenal luminescent characteristic for 5D3,2,1,0 → 7Fj transitions. The concentration dependence of the chromatic behavior indicates that these nanophosphors are promising candidate for the single-phased or red-blue-green (RGB) phosphor based white LEDs with near ultra-violet excitation.
Keywords: Optical Materials, Chemical Synthesis, X-ray diffraction, Optical Properties, Crystal structure, Luminescence.