Engineering Tunable Broadband Near‐Infrared Emission in Transparent Rare‐Earth Doped Nanocrystals‐in‐Glass Composites via a Bottom‐Up Strategy

Abstract Applications of trivalent rare earth (RE³⁺)‐doped light sources in solid‐state laser technology, optical communications, biolabeling, and solar energy management have stimulated a growing demand for broadband emission with flexible tunability and high efficiency. Codoping is a conventional strategy for manipulating the photoluminescence of active RE³⁺ ions. However, energy transfer between sensitizers and activators usually induces nonradiative migration depletion that brings detrimental luminescent quenching. Here, a transparent framework is employed to assemble ordered RE³⁺‐doped emitters to extend the emission spectral range by extracting photons from a variety of RE³⁺ ions with sequential energy gradient. To block migration‐mediated depletion between different RE³⁺ ions, a nanoscopic heterogeneous architecture is constructed to spatially confine the RE³⁺ clusters via a “nanocrystals‐in‐glass composite” (NGC) structure. This bottom‐up strategy endows the obtained RE³⁺‐doped NGC with high emission intensity (nearly one order of magnitude enhancement) and broadband near‐infrared emission from 1300 to 1600 nm, which covers nearly the whole low‐loss optical communication window. Most crucially, NGC is a versatile approach to design tunable broadband emission for the potential applications in high‐performance photonic devices, which also provides new opportunities for engineering multifunctional materials by integration and manipulation of diverse functional building units in a nanoscopic region.