Magnetic- and electric-dipole radiative rates in multifunctional Ba5Zn4Y8O21:Tb3+ nanorods

Abstract

Novel multifunctional Ba5Zn4Y8O21:Tb3+ nanorods, fabricated via solution combustion route, have been found to go in the tetragonal system with the I4/m (87) crystallographic space group. The diffuse reflectance (DR) studies unveiled a band-gap of 3.77 eV for Ba5Zn4Y7.84Tb0.16O21 (most emitting composition). The ultra-violet (UV) excitation at a wavelength of 290 nm for all Ba5Zn4Y8O21:Tb3+ samples produced the characteristics emission peaks corresponding to 5D4 → 7F6,5,4,3 transitions in Tb3+ (used to obtain Judd–Ofelt parameters). The critical distance of energy transfer between neighboring Tb3+ ions was found to be 18.62 A, and helped to shortlist the right mechanism responsible concentration quenching phenomena (dipole–quadrupole). The in-depth analysis of photoluminescence (PL) decay curves and emission spectra of Ba5Zn4Y8O21:Tb3+ nanorods delivered the value of radiative lifetime (1.1934 ms) and total radiative rates from 5D4 state in Tb3+. The radiative probabilities of electric-dipole transitions (extracted from total radiative rates i.e. magnetic-dipole + electric-dipole) were used to calculate the Judd–Ofelt intensity parameters (Ω2 = 3.98 × 10−20, Ω4 = 1.76 × 10−20 and Ω6 = 0.28 × 10−20 cm2). The quantum efficiency of 5D4 state in Ba5Zn4Y7.84Tb0.16O21 phosphor was calculated to be 79% with pure green emission, signifying their potential use in display and lighting devices. As a final point, the high magnitude of emission cross-section of 5D4 → 7F5 (14.84 × 10−20 cm2) transition also claims their promising candidature as a good laser crystal.