First-principles investigation of structural, electronic, optical, and thermoelectric properties of Mn2+-Substituted NaAl11O17 phosphor compounds for advanced optoelectronic applications

The development of high-performance materials for optoelectronic and thermoelectric applications is a key area of contemporary research. This study presents a comprehensive first-principles investigation into the structural, mechanical, electronic, optical, and thermoelectric properties of pristine NaAl₁₁O₁₇ and its Mn²⁺-Substituted counterpart, [NaAl₁₁O₁₇]:Mn²⁺, utilizing density functional theory (DFT) within the GGA + U framework. Our findings reveal that Mn²⁺ doping significantly modifies the electronic structure of NaAl₁₁O₁₇, reducing its bandgap from 4.49 eV to 1.1 eV (spin-up) and 3.9 eV (spin-down). This substantial bandgap reduction enhances the material's optoelectronic properties, positioning [NaAl₁₁O₁₇]:Mn²⁺ as a promising candidate for light-emitting diodes (LEDs), photovoltaic devices, and display technologies.

The mechanical properties of the Substituted material demonstrate improved ductility and elastic stability, which are crucial for flexible device applications. Optical analyses, including dielectric function, absorption coefficient, refractive index, and reflectivity, indicate enhanced absorption in the visible range and stronger interaction with electromagnetic radiation upon doping. These changes are attributed to the introduction of localized Mn-derived states near the Fermi level, facilitating efficient electron excitation and radiative recombination processes.

Thermoelectric evaluations reveal notable improvements in the Seebeck coefficient, electrical conductivity, and a marked decrease in thermal conductivity for the Substituted compound. The synergistic effect of these parameters yields an enhanced figure of merit (ZT), increasing from 0.01 in pristine NaAl₁₁O₁₇ to 0.12 at elevated temperatures for [NaAl₁₁O₁₇]:Mn²⁺. This enhancement stems from increased phonon scattering due to Mn incorporation and the favorable electronic structure modifications. Furthermore, effective mass calculations highlight that Mn²⁺ doping slightly increases the electron and hole effective masses, promoting carrier localization and improving luminescence efficiency.

Overall, this work underscores the transformative potential of Mn²⁺ doping in tailoring the physical properties of NaAl₁₁O₁₇, making [NaAl₁₁O₁₇]:Mn²⁺ a compelling material for next-generation optoelectronic and thermoelectric applications. The insights derived from this study not only deepen the understanding of doping effects in complex oxides but also pave the way for designing eco-friendly and efficient energy conversion devices.