Divalent Europium-containing colloidal metal halide nanocrystals for light-emitting applications
Ho Young Woo1, Mi Yeon Yu2, Seung Hyeon Kim2
1School of Integrative Engineering, Chung-Ang University, Seoul, 06974, Republic of Korea.
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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 (Eu2+) 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 Eu2+ 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 Eu2+, 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 Eu2+ PL mechanism and synthesis of phase-pure MHNCs is essential for the advancement of Eu2+-based MHNCs as novel emitters. This review summarizes recent developments in Eu2+-based colloidal MHNCs and their PL properties. First, the local factors affecting the luminescence properties of Eu2+ in inorganic hosts are discussed. Subsequently, recent advances in the synthesis of Eu2+-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.
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