Optical Excitations And Ferromagnetic Ordering In Sm Doped Wo3 At Dilute Concentrations

Sm doped WO3 (hereafter referred as WO3:Sm) compounds were synthesized via conventional solid-state reaction method and characterized for their structural, optical, and magnetic properties. X-ray diffraction (XRD) and the Rietveld refinement studies along with the Raman spectroscopy confirm that these compounds are of monoclinic phase [space group- P2(1)/n] with absence of impurities. Scanning Electron Microscopy (SEM) reveals that particles are densely packed with irregular morphologies. The UV-vis spectra show the band gap broadening with Sm doping due to the Burstein-Moss shift. The Photoluminescence studies (PL) under 320 nm excitation exhibit a broad-band of violet-blue emissions originating from oxygen vacancy defects of WO3. At 450 nm excitation, WO3:Sm samples show diffused Sm3+ emissions that could be due to the strong electron-phonon coupling between Sm ions and host lattice. The values of Commission Internationale de l'Elcairage (CIE) chromaticity coordinates and correlated color temperature (CCT) endorse cool white-light emission under 400 nm excitation making them a promising candidate for white LEDs. Magnetic measurements in these samples show the presence of room-temperature ferromagnetism (RTFM). The origin of the FM behavior is understood based on the bound magnetic polaron (BMP) mechanism and the magnetic data fit well with the BMP model.