Abstract
Judd-Ofelt (J-O) theory has been applied to a series of LiLa1-xEux(PO3)(4) (x = 5%; 10%; 15%; 20% and 30%) polycrystalline powders based on their emission spectra. J-O intensity parameters Omega(lambda) (lambda = 2, 4) and various radiative properties such as the radiative transition probability (A), radiative life time (tau(R)), branching ratio (beta(R)) and stimulated emission cross-section (sigma(e)) have been determined. The observed trend for J-O parameters (Omega(2) < Omega(4)) reveals the ionic character of La(Eu)-O bond as well as the symmetry environment around the Eu3+ ion in LiLa(PO3)(4). The experimental decay curves of the D-5(0) level in LiLa1-xEux(PO3)(4) have a single exponential profile. The registered long life time, low multiphonon relaxation rates (W-NR), high quantum efficiency (eta) and the best optical gain parameter (sigma(e) x tau(exp)) have been discussed as function of Eu3+ concentration, chemical composition and crystal structure of the host matrix and particle-size distribution. A comparative study reveals that LiLa1-xEux(PO3)(4) is promising for use in optical devices as well as for developing visible red lasers to emit at 613 nm. The optical band gap energies of LiLa1-xEux(PO3)(4) have been calculated from the diffuse reflection spectral measurements. The results were discussed as a function of Eu3+ concentration and compared to reported theoretical results. (C) 2014 Elsevier B.V. All rights reserved.