Energy transfer and photoluminescent analysis of a novel color-tunable Ba2Y1-xV3O11:xSm3+ nanophosphor for single-phased phosphor-converted white LEDs

Abstract

Metal nitrates are used to synthesize a series of novel Ba2Y1-xV3O11:xSm3+ nanophosphors via urea-assisted solution combustion route. X-ray diffraction (XRD), diffuse reflectance (DR), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were employed to analyse the structure, morphology, photoluminescent behaviour and energy transfer mechanism. Rietveld analysis over Ba2Y0.98Sm0.02V3O11 showed that Y3+ ions can be well-replaced by trivalent samarium ions without resulting any major alteration in the crystal structure of host lattice. Furthermore, the lattice parameters were determined for both the host as well as the doped composition. The Scherrer equation yielded an average particle size of 44 nm, which in turn was further confirmed by TEM micrographs. The optical band-gap of the host (3.92 eV) was calculated from the diffuse reflectance spectra. Moreover, the photoluminescence spectral studies showed that under near ultra-violet (NUV) excitation of 340 nm, our nanophosphor powder exhibits the characteristic emission peaks of trivalent samarium along with the emission of VO43− (501 nm) group. The excitation energy transfer from vanadate group to Sm3+ produced a systematic color tunablity in white region itself. The optimum Sm3+ concentration for better luminescence was found to be 2 mol%. The critical distance for energy transfer was calculated to be 29.02 Å, which in turn assisted to shortlist the mechanism responsible for luminescence-quenching (dipole-dipole) arising from the over-doping of the activator. The photoluminescence decay curves revealed the decay kinetics of 4G5/2 electronic state. Finally, the calculation of CIE color coordinates from emission spectra in MATLAB program unveiled a somewhat white-light emitter which may find potential applications in phosphor-converted white light emitting diodes (PC-WLED) under near-ultraviolet (NUV) excitation.