Tunable Yellow-white-blue Self-trapped Exciton Emissions of Double Perovskites Cs₂Na_0.9Ag_0.1In_1-xZr_xCl₆

Double perovskite materials exhibit broad application prospects in light-emitting diodes (LEDs), optical anti-counterfeiting, and display technologies, due to their exceptional optoelectronic properties. However, conventional double perovskite phosphors still face several challenges in practical applications, such as energy loss caused by the reabsorption effect in multi-component phosphors, stability issues arising from differential aging rates among components, and limitations in large-scale production due to complex synthesis processes. Additionally, single-component double perovskite materials (LHDPs) often struggle to achieve broad-spectrum tunable emission, restricting their utility in multicolor luminescence and white-light LEDs. To address these challenges, an innovative Zr⁴⁺ doping strategy was proposed, aiming at modulating the crystal structure and electronic band structure of Cs₂Na_0.9Ag_0.1InCl₆ double perovskites to achieve efficient single-component broadband emission. Specific objectives include: (1) optimizing the bandgap structure via Zr⁴⁺ doping to enhance exciton localization, (2) revealing the regulatory mechanism of Zr⁴⁺ on dual emission channels of self-trapped excitons (STEs) and (3) developing phosphors with high photoluminescence quantum yield (PLQY) and tunable correlated color temperature (CCT) for applications in white-light LEDs and optical anti-counterfeiting.

A series of Cs₂Na_0.9Ag_0.1InCl₆ double perovskite phosphors with varying Zr⁴⁺ concentrations (0%-100%) were synthesized by using chemical coprecipitation method. Morphology and elemental distribution were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), confirming uniform micron-sized octahedral structures. X-ray diffraction (XRD) analysis revealed a highly crystalline face-centered cubic structure, with diffraction peaks shifting toward higher angles as, Zr⁴⁺ concentration was increased, indicating lattice contraction. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to study the influence of Zr⁴⁺ on the electronic structure. Optical properties were systematically evaluated using UV-Vis absorption and photoluminescence (PL)spectroscopy, complemented by temperature-dependent PL 80-320 K) and fluorescence lifetime analysis to elucidate the luminescence dynamics. Notably, tunability of the emission color was explored by varying excitation wavelengths (254-360 nm) and Zr⁴⁺ doping levels, with chromaticity coordinates (CIE) and CCT calculated for each condition.

Zr⁴⁺ successfully substituted In³⁺/(Ag⁺/Na⁺) sites, forming stable [ZrCl₆]²-octahedra, which induced lattice distortion and electron cloud rearrangement. A significant enhancement in the [ZrCl₆]²-absorption band at 254 nm was observed with increasing content of Zr⁴⁺, while PL spectra exhibited dual-peak emission (blue and yellow), confirming the establishment of dual-channel STE1 (yellow) and STE2 (blue) emission mechanisms. Under optimized conditions (Zr⁴⁺=40%), the material achieved a PLQY of 86.9% under 334 nm excitation. Under 254 nm excitation, competitive blue-yellow emission yielded standard white light (CIE: 0.28, 0.36) with a PLQY of 70.6% and tunable CCT (4000-10000 K). Temperaturedependent PL analysis demonstrated excellent thermal stability (E_b=100.992 meV), while lifetime measurements indicated prolonged exciton recombination due to Zr⁴⁺ doping, effectively suppressing non-radiative decay.

Precise control over dual STE emission channels in Cs₂Na_0.9Ag_0.1InCl₆ double perovskites via Zr⁴⁺ doping was demonstrated, overcoming the limitation of non-tunable emission in single-component materials. Zr⁴⁺ incorporation not only activated blue emission through lattice distortion but also enhanced the radiative efficiency via exciton localization. The optimized phosphors exhibited outstanding performance, including high PLQY (≈86%) and tunable white-light emission(CCT=4000-10000 K), thus offering a novel material platform for next-generation optical anti-counterfeiting and white-light LEDs. Future research may focus on multi-metal co-doping to further manipulate STE dynamics and expand optoelectronic applications.