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

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 \({\epsilon }_{2}\left(\omega \right)\) plots that the investigated hexafluorides absorb maximum photons in the UV region. Based on the \(R\left(\omega \right)\) 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.