To Dope Mo 3+ in Colloidal Nanocrystals

ABSTRACT Mo 3+ shows intra‐configurational spin‐flip (ICSF) d → d electronic transitions, emitting near‐infrared‐II (NIR‐II) radiation. Till date, the emission has been reported from Mo 3+ ‐doped into bulk host materials, in the powder or single crystalline forms. Here we report the synthesis of Mo 3+ doping in a colloidal nanocrystal (NC). Colloidal Mo 3+ ‐doped Cs 2 AgInCl 6 double perovskite NCs are prepared using a typical hot‐injection method in a non‐polar medium. The challenges of poor solubility of molybdenum precursor and instability of low oxidation state of Mo 3+ in the reaction medium are overcome by a rational design of the synthesis. The resulting NCs have cubic shape with edge length ∼9 nm, and oleylammonium ions as the predominant surface capping ligands. The colloidal synthesis enabled us to fabricate thin films of Mo 3+ ‐doped NCs by spin‐coating technique. Both colloidal NCs and their films show the sharp Mo 3+ ICSF NIR‐II emission around 1105 nm. Temperature dependent (7‐300 K) PL spectra and lifetime studies provide mechanistic insights about the spin‐ and Laporte‐selection rules of the ICSF emission from [MoCl 6 ] 3− octahedral unit. This report of a colloidal NC with Mo 3+ dopants, and their thin films, is expected to open up research avenues for micro‐LEDs and quantum light emitters in NIR‐II region.