Highly efficient and thermally stable Eu3+ activated phosphate based phosphors for wLEDs: An experimental and DFT study
Journal
Journal of Alloys and Compounds
Journal Volume
895
Date Issued
2022
Author(s)
Abstract
Europium ions-activated alkali- alkaline phosphate phosphors with sharp red-light emission were designed via compositional ternary phase diagram for the first time. A number of polyphosphate phosphors including Eu3+ activated NaCa(PO3)3 were prepared via solid state reaction route. The synthesized phosphors exhibited narrow red light emissions around 612 nm initiating from Eu3+ f-f transitions. Corresponding excitation spectra of Eu3+ ions in the present host displayed characteristics f-f transition along with a charge transfer (CT) band. Origin of CT band was clarified utilizing band structure and density of states (DOS) analysis via Density functional theory (DFT). Experimentally calculated band gap was obtained as 5.59 eV and verified through band structure analysis. The concentration quenching mechanism was explored by varying the Eu3+ concentration, revealing 4 mol% as the optimum concentration and the quenching was controlled via dipole–dipole interaction. High thermal stability (~90.17%) was correlated with structural rigidity related to bond length distortion index evaluated using DFT. The Internal quantum yield (IQY) of prepared phosphors was obtained as ~86%. Additionally, Judd-Ofelt (JO) theory was utilized to assess local surrounding environment nearby europium ion in NaCa(PO3)3 host. In addition, near ultraviolet (NUV) chip was coated with the NaCa0.96Eu0.04(PO3)3 and commercial blue and green-light-emitting phosphors to fabricate the white light emitting diode (wLED). The fabricated LED showed high color-rendering-index (CRI) of 85.1 and suitable correlated-color-temperature (CCT) of 5661 K. The results suggested that the Eu3+ activated NaCa(PO3)3 phosphors were suitable for white LEDs. ? 2021
Subjects
Density functional theory
Judd-Ofelt theory
Phosphor
Photoluminescence
White light emitting diode
Bond length
Calcium compounds
Charge transfer
Energy gap
Ions
Light emitting diodes
Phosphors
Quenching
Sodium compounds
Solid state reactions
Thermodynamic stability
Activated phosphates
Charge transfer bands
Density functional theory studies
Density-functional-theory
Europium ions
F-f transitions
Red-light emission
Thermally stable
White light emitting diodes
Europium compounds
Type
journal article