Divalent Europium-containing colloidal metal halide nanocrystals for light-emitting applications.

Lanthanide-based inorganic nanomaterials have been widely utilized as luminescent materials for broad-ranging applications in lighting, display, and optoelectronic devices. Among lanthanide elements, divalent europium (Eu) has recently gained significant attention owing to its excellent photoluminescence (PL) properties, such as a short radiative decay lifetime, narrow PL bandwidth, and wide emission range from ultraviolet to near-infrared. Particularly, colloidal metal halide nanocrystals (MHNCs) offer unique advantages as inorganic hosts for Eu owing to their excellent phase purity, chemical and optical stability, and colloidal stability for facile integration via solution processes. In addition, the PL properties of Eu, originating from the parity-allowed 4f-5d transitions, can be precisely controlled by tuning the phase and compositions of MHNCs. Therefore, an in-depth understanding of the Eu PL mechanism and synthesis of phase-pure MHNCs is essential for the advancement of Eu-based MHNCs as novel emitters. This review summarizes recent developments in Eu-based colloidal MHNCs and their PL properties. First, the local factors affecting the luminescence properties of Eu in inorganic hosts are discussed. Subsequently, recent advances in the synthesis of Eu-based MHNCs using different host-dopant frameworks, their optical proprieties, and applications are outlined. This comprehensive review provides valuable insights for designing high-performance emitters, particularly for achieving deep-blue emission in light-emitting diodes and high-energy scintillators.