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Efficient optical modulation enables a significant improvement of optical conversion efficiency and regulation of optical response rate, showing great potential for optoelectronics applications. However, the weak interaction between photons poses a strong obstacle for manipulating photon–photon interactivity. Here, upon simultaneous excitation of 850 and 1550 nm, a fast–slow optical modulation of green up‐conversion (UC) luminescence in oxyfluoride glass ceramics containing NaYF4:Er3+ nanocrystals can be achieved. Compared with the sum of luminescence intensity excited by the two single‐wavelengths, green UC luminescence excited by simultaneous two‐wavelength presents an obvious increase by approximate six times. Interestingly, the response rate of green UC luminescence relies on the pump strategy of two‐wavelength excitation, showing as high as two times of the fast–slow response difference. The fast–slow optical modulation of green UC luminescence under two‐wavelength excitation is promising for emerging applications in all‐optical switching. [ABSTRACT FROM AUTHOR]

Rare earth (RE) ions‐doped luminescent nanocrystals (NCs) with numerous unique advantages have attracted tremendous interest for the wide applications from science to engineering, yet suffering from the shortcoming of thermal quenching coming from surface organic ligands. We propose utilizing a facile acid‐base reaction to remove surface organic ligands introduced choosing carboxylic acids as stabilizing agent and weaken thermal quenching. The results showed that the acid‐base reaction displayed an outstanding cleaning effect. After acid‐treatment, most surface organic ligands were removed, and there was no influence on crystal structure and morphology of as‐prepared β‐NaYF4:Er3+ NCs. Meanwhile, with no surface organic ligands capping, β‐NaYF4:Er3+ NCs preferred brighter emission after thermal treatment, including up‐conversion (UC), near‐infrared (NIR), and mid‐infrared (MIR) emission. When calcined the acid‐treated β‐NaYF4:Er3+ NCs in different atmosphere, such as oxygen and reducing atmosphere (15%H2 + 85%N2), an unexpected enhancement of all emission bands in Er3+ was determined under phase transformation temperature, especially in oxygen atmosphere. Furthermore, all the fluorescence lifetimes of Er3+ also exhibited obvious extension. Our results supposed that the β‐NaYF4:Er3+ NCs have promising applications in safety ink, and the acid‐treatment by diluted hydrochloric acid is a general approach to remove deleterious organic ligands on NC surface further to weaken thermal quenching. [ABSTRACT FROM AUTHOR]

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. A tunable broadband emission is demonstrated by assembly of ordered rare‐earth‐doped emitters with sequential energy gradient. Migration‐mediated energy quenching has been successfully suppressed by nanoscopic heterogeneous structures constructed in transparent nanocrystals‐in‐glass composites. This assembly strategy highlights the possibility to fabricate multifunctional materials by linking different building units with photonic, magnetic, and electronic properties in a transparent framework. [ABSTRACT FROM AUTHOR]

Mid-infrared (MIR) laser operating at 2–5 μm has gained increasing interest because of the extensive applications in fields from biomedicine, sensing to nanomaterial science. Chalcogenide glass (ChG) is a kind of matrix that is promising for MIR laser due to its low phonon energy and wide infrared transmittance region. However, significant challenges in the enhancement of MIR optical properties of rare-earth ion-doped ChGs still exist. Here, enhanced MIR emission was realized in Pr3+-doped chalcogenide glass ceramics (ChGCs). By controlling the heat treatment temperature and duration, biphasic-phase nanocrystals of Ga 2 Se 3 and GeSe 2 were successively precipitated in the glass host. Compared to the as-prepared glass, the GCs exhibit an obvious increase in emission intensity by more than 5 times. The improvement of the MIR emission may be induced by the enhanced cross-relaxation between Pr3+ ions and the increased multiple scattering effects. Furthermore, the obtained ChGC enables large stimulated emission cross section 0.42 × 10−20 cm2 at 2.44 μm and 0.62 × 10−20 cm2 at 4.75 μm. The superior optical properties of the ChGC indicate that it is an attractive candidate for MIR laser. • Biphasic-phase nanocrystals of Ga 2 Se 3 and GeSe 2 embedded glass-ceramic was prepared by controlled heat treatment. • Enhanced MIR emission of Pr3+ was observed in the glass ceramics. • Effect of biphasic-phase nanocrystals on the enhancement of MIR emission was investigated. • The glass-ceramic with large stimulated emission cross section endows its potential application in MIR laser. [ABSTRACT FROM AUTHOR]