Investigation of structural and optoelectronic integrity of Sm3+ doped CaWO4 for LED applications

Abstract

In this study we illustrate the structural, electronic and optical integrity of Ca1-xSm(2/3)xWO4 (x = 0.00, 0.02, 0.04, 0.06 and 0.08) crystals for optoelectronic applications via experimental and first principles approach. According to our experimental outcomes, CaWO4 crystallizes in scheelite type tetragonal structure devoid of impurity which depends on the A-site cationic radius and dopant-host compatibility. As a result, the dopant induced lattice distortion occur due to symmetric and asymmetric stretching of (Ca, Sm)—O and W–O bonds within [CaO8] and [WO4] cluster. According to our FT-IR and Raman spectral analysis, the non-centrosymmetric vibration within the [WO4]2- complex gives rise to internal modes while the Ca2+/Sm3+ cationic displacement and rigid molecular ionic group constitutes the external modes which equally impacts the electronic and optical characteristics of the host material. While the forbidden gap extends due to Sm3+ substitution, the delocalization of W-5d orbitals on the other hand occur due to rising distortions within the WO4 cluster. As a result, the polarization between [WO4] and [CaO8] cluster and difference in the electronic transitions controls the optical characteristics of the host material. According to our experimental and theoretical predictions, a noticeable decrease in the optical band gap (5.96–5.83 eV) occurs due to heterovalent cationic substitution (Sm3+), difference in structural order-disorder and charge carrier density. As a result, a broad photoluminescence (PL) spectrum among acceptor doped samples verifies the impact of multi-phonon or multi-level processes on the luminosity of the host material.