Magnetic- and electric-dipole radiative rates in multifunctional Ba5Zn4Y8O21:Tb3+ nanorods
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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 Å, 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.
One of the authors, Ms. Jyoti Dalal gratefully acknowledges the financial support in the form of senior research fellowship (SRF) from Council of Scientific and Industrial Research (CSIR), New Delhi, India (Award No: 09/382(0180)/2016-EMR-I).
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