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<p>The development of environmentally benign materials with tunable optical and plasmonic responses is essential for next-generation photonic, optoelectronic, and sustainable energy technologies. In this work, we investigate the structural, electronic, optical, plasmonic, and thermoelectric properties of lead-free Rb₂AgSbX₆ (X = Br, I) double perovskites using first-principles calculations based on density functional theory. Structural optimization confirms the formation of stable cubic phases with favorable tolerance factors and negative formation energies, indicating good thermodynamic stability<b>.</b> Mechanical stability was further confirmed from the calculated elastic constants, which satisfy the Born stability criteria for cubic crystals, while the tolerance and octahedral factors support the structural stability of the perovskite phase. The electronic structure calculated using the mBJ-GGA approach reveals direct band gaps of 1.82&#xa0;eV and 1.06&#xa0;eV for Rb₂AgSbBr₆ and Rb₂AgSbI₆, respectively, indicating that Br → I substitution reduces the band gap and shifts the optical response toward lower photon energies; this trend, together with the increase in static dielectric constant from 4.097 to 5.675 and refractive index from 2.024 to 2.382, demonstrates the effective role of halide substitution in tuning the electronic and optical properties for optoelectronic and photovoltaic applications. The optical analysis shows strong absorption in the visible–ultraviolet region, high optical conductivity, and significant dielectric response, confirming efficient light–matter interaction. In particular, the energy loss function reveals distinct peaks associated with collective electronic oscillations, indicating moderate plasmon-like features associated with collective electronic excitations, although their plasmonic strength is expected to be lower than that of conventional metallic plasmonic materials. These moderate plasmon-like features, together with the high absorption coefficient, optical conductivity, and dielectric response, suggest the potential relevance of these lead-free double perovskites for UV optoelectronic, optical-filtering, photodetection, and sensing-related applications, although further experimental validation is required. Furthermore, thermoelectric calculations performed using BoltzTraP under the constant relaxation-time approximation, combined with lattice thermal conductivity estimated from the Slack model, show favorable Seebeck coefficients and figure-of-merit values approaching 0.8 at high temperatures up to 800&#xa0;K, highlighting their additional potential for waste-heat recovery. Overall, Br → I substitution effectively tunes the electronic, optical, plasmon-like, and transport properties of Rb₂AgSbX₆ double perovskites, highlighting their potential as lead-free multifunctional materials for sustainable optoelectronic and energy-conversion applications.</p>

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First-Principles Investigation of Optical and Plasmonic Response of Lead-Free Rb₂AgSbX₆ (X = Br, I) Double Perovskites

  • 期刊论文

  • 发表日期：

    2026年7月10日

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  • K. Bouferrache,
  • M. A. Ghebouli,
  • M. Fatmi,
  • Faisal K. Alanazi,
  • Samah Saidi,
  • Talal M. Althagafi,
  • Aseel Smerat,
  • Murat Yaylacı

摘要

The development of environmentally benign materials with tunable optical and plasmonic responses is essential for next-generation photonic, optoelectronic, and sustainable energy technologies. In this work, we investigate the structural, electronic, optical, plasmonic, and thermoelectric properties of lead-free Rb₂AgSbX₆ (X = Br, I) double perovskites using first-principles calculations based on density functional theory. Structural optimization confirms the formation of stable cubic phases with favorable tolerance factors and negative formation energies, indicating good thermodynamic stability. Mechanical stability was further confirmed from the calculated elastic constants, which satisfy the Born stability criteria for cubic crystals, while the tolerance and octahedral factors support the structural stability of the perovskite phase. The electronic structure calculated using the mBJ-GGA approach reveals direct band gaps of 1.82 eV and 1.06 eV for Rb₂AgSbBr₆ and Rb₂AgSbI₆, respectively, indicating that Br → I substitution reduces the band gap and shifts the optical response toward lower photon energies; this trend, together with the increase in static dielectric constant from 4.097 to 5.675 and refractive index from 2.024 to 2.382, demonstrates the effective role of halide substitution in tuning the electronic and optical properties for optoelectronic and photovoltaic applications. The optical analysis shows strong absorption in the visible–ultraviolet region, high optical conductivity, and significant dielectric response, confirming efficient light–matter interaction. In particular, the energy loss function reveals distinct peaks associated with collective electronic oscillations, indicating moderate plasmon-like features associated with collective electronic excitations, although their plasmonic strength is expected to be lower than that of conventional metallic plasmonic materials. These moderate plasmon-like features, together with the high absorption coefficient, optical conductivity, and dielectric response, suggest the potential relevance of these lead-free double perovskites for UV optoelectronic, optical-filtering, photodetection, and sensing-related applications, although further experimental validation is required. Furthermore, thermoelectric calculations performed using BoltzTraP under the constant relaxation-time approximation, combined with lattice thermal conductivity estimated from the Slack model, show favorable Seebeck coefficients and figure-of-merit values approaching 0.8 at high temperatures up to 800 K, highlighting their additional potential for waste-heat recovery. Overall, Br → I substitution effectively tunes the electronic, optical, plasmon-like, and transport properties of Rb₂AgSbX₆ double perovskites, highlighting their potential as lead-free multifunctional materials for sustainable optoelectronic and energy-conversion applications.