A comparative study on the impact of cation replacements on the structural, optoelectronic and thermodynamic characteristics of hexafluorides red phosphors Cs2MF6 (M = C, Ge, Pb, Si) using first-principles calculations: a prospect for warm-white LEDs (w-LEDs) applications

Abstract

In order to address the energy challenges of the near future, researchers are currently focused on developing environmentally friendly and energy-efficient phosphors for luminescence devices such as light-emitting diodes (LEDs). When it comes to this topic, older lighting devices such as halogen lamps, LCD backlights, incandescent lamps, and fluorescent lamps can be substituted with advanced next-generation lighting technology created with phosphor-transformed white LEDs. We've conducted a detailed analysis of the structural and optoelectronic characteristics of Cs-based phosphors Cs2MF6 (M = C, Ge, Pb, Si) for potential use in photoluminescence as well as photovoltaic applications such as LEDs. Utilizing the GGA scheme allows for an in-depth analysis of exchange and correlation energy potentials within density functional theory (DFT) first-principles calculations. The calculated structural properties reveals that Cs2PbF6 is the most stable compound among Cs2MF6 (M = C, Ge, Pb, Si) as they possess lowest ground state energy. Direct bandgaps of 1.57, 1.459, 1.481, and 1.59 eV are observed with the presence of intermediate bands for Cs2CF6, Cs2GeF6, Cs2PbF6, and Cs2SiF6, respectively. It is established by analyzing epsilon(2)(w) plots that the investigated hexafluorides absorb maximum photons in the UV region. Based on the R(w) spectra, it is evident that Cs2MF6 (M = C, Ge, Pb, Si) act as weak reflectors of incident photons in the visible and IR regions. However, around 40% of the incoming photons get reflected at various energies by individual compounds. Thermodynamic characteristics of these hexafluorides reveals that they are thermodynamically stable compounds.