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Near-infrared (NIR) emitting materials find a variety of applications in photodynamic therapy, national security, food inspection, and bioimaging, but achieving efficient NIR luminescence in lead-free perovskite materials is still challenging. Herein, we synthesized a series of lead-free Mo4+alloyed Cs2ZrCl6vacancy-ordered double perovskites with different Mo concentrations. These materials display tunable dual luminescence bands due to intrinsic host emission in the blue region and dopant induced d–d transitions emitting in the NIR region. Host- and dopant-induced emission can be excited at different energies, as revealed by spectroscopic studies. Minimum interaction between the host and dopant octahedra accounts for the dual emission in these 0D materials, further confirmed by density functional theory (DFT) calculations. Alloying Mo4+reduces the band gap of these materials and DFT calculations confirm that the decrease in band gap is due to the increased contribution of Mo 4d states at the conduction band minima. Moreover, the structural stability of the host material also increases after Mo4+alloying. Our study explored the tunable dual band emission in visible and NIR regions and enhanced structural stability in Mo4+alloyed Cs2ZrCl6, thereby opening new avenues in the development of Pb-free NIR-emitting phosphors.

Lead-free halide double perovskites (DPs) have emerged as a stable and greener alternative to very toxic lead-based perovskites owing to their outstanding photophysical properties. Here, a series of Cs2(NaxAg1–x)BiBr6(x= 0, 0.25, 0.5, 0.75, and 1) double-perovskite nanocrystals (NCs) are synthesized, which have not been much explored yet. The formation of highly miscible Cs2(NaxAg1–x)BiBr6solid solutions is favored because of very low lattice mismatch between Cs2NaBiBr6and Cs2AgBiBr6. These DP NCs have tunable band gaps, which successively increase with increasing Na/Ag ratio, enabling us to tune their band gap by more than 0.5 eV. The band gap tuning is further confirmed by electronic structure calculations using density functional theory (DFT), which is in line with the band gap estimated from the absorption data. The Cs2(NaxAg1–x)BiBr6(x= 0, 0.25, 0.5) DP NCs are found to be more stable in the ambient conditions than the Cs2(NaxAg1–x)BiBr6(x= 0.75, 1.00) DP NCs.

The layered hybrid double perovskites (LDPs) possess excellent stability and environmental friendliness, which makes them remarkable semiconducting materials. Contrary to significant advancements, the nonfluorescent nature at ambient temperature and pressure is still a major hurdle in this intriguing family. Here, we demonstrate doping of the transition metal cation Mn2+in two-dimensional (2D) (PEA)4NaInCl8(PEA = phenylethylamine) LDP, by a solution-processed crystallization method. This results in broadband emission at ambient conditions and initial contraction followed by expansion of host lattice on increasing dopant concentration. A higher dopant feed ratio in this wide band gap material leads to the absorption at 2.95 eV due to the 6A1(6S) → 4A1(4G) transitions on Mn2+centers. First-principles calculations based on density functional theory (DFT) confirm that Mn2+in substitutional sites results in lattice contraction while interstitial site Mn2+doping leads to lattice expansion. The potential of Mn2+to improve optical and magnetic properties of host lattice and a deeper understanding of distribution of Mn2+dopant make these LDPs a promising material for emitters for solid-state lighting and magneto-optical applications.

Lanthanide ions (Ln3+) are well-known dopants for controlling the optoelectronic properties of double perovskites (DPs). However, the excitation energy of Ln3+-doped Cs2AgInCl6being too high (∼250–290 nm) limits its direct excitation by commercial UV light-emitting diodes (≥365 nm). To overcome this challenge, we employed Bi3+as a sensitizer to induce the emission of Sm3+at much lower excitation energy in Sm3+–Bi3+codoped Cs2AgInCl6DP nanocrystals (NCs). Spectral analysis shows that a trace amount of Bi3+(∼1%) doping provides dual emission of self-trapped excitons (STEs) and characteristic emissions of Sm3+assigned to 4G5/2to 6HJ(J= 5/2, 7/2, 9/2, and 11/2) transitions with 368 nm excitation energy. Transient absorption spectroscopic results revealed the existence of nonradiative energy transfer from STE states. Subsequently, we propose a mechanism to explain the formation of energy-transfer channels from STEs to excited states of Sm3+. Our study demonstrates that Bi3+can efficiently sensitize Sm3+to modify the optical properties of lead-free DP NCs to expand their luminescence application.