The luminescence properties of stable chloride double perovskites Cs2BIInCl6, where BI is 4 at.% Ag, 6 at.% Na, doped with Sb3+ and Er3+ were investigated for the first time in the 250-1600 nm region and revealed significant potential for advanced application. We employed XPS and ToF-SIMS for chemical analyses, while SEM, XRD, and Raman spectroscopy provided insights into the morphology, crystal structure, and vibrational characteristics of the samples. The crystal structures of Cs2Ag0.292Na0.708InCl6, Cs2Ag0.285Na0.715In0.971Er0.029Cl6, Cs2Ag0.16Na0.84In0.893Er0.017Sb0.09Cl6 were examined using single-crystal methods. The excited Sb3⁺ ions emitted blue light at 450 nm due to electronic absorption at sub-band gap levels, facilitating energy transfer to Er3⁺ ions. Notably, the Er3⁺ emitted radiation at 1540 nm, a wavelength particularly useful for optical communication applications. Additionally, emissions at 525 nm, 552 nm, 665 nm, and 805 nm were observed, corresponding to f-f transitions of Er3⁺ ions. These compelling results were supported with calculations based on the Modified Crystal Field Theory, explaining the effects of varying concentrations of Sb3⁺ and Er3⁺ on the crystal structure and luminescent properties. By using the synthesized materials, we successfully developed an LED prototype that utilized a UV chip (320 nm) combined with the Cs2Ag0.4Na0.6In0.9Er0.01Sb0.09Cl6 powder as a stable and effective luminophore for possible application in optoelectronics.
