CaZnOS:Nd³⁺ Emits Tissue-Penetrating near-Infrared Light upon Force Loading

Mechanoluminescent (ML) materials are mechano-optical converters that can emit light under an external mechanical stimulus. All the existing ML materials can only emit light from near ultraviolet to red, which is outside the near-infrared (NIR) windows desired for biomechanical imaging. No studies have been done on doping rare earth (RE) ions with photoluminescence (PL) in the NIR region into a compound to form a ML material that emits NIR light in response to an external force. Here, we show that doping RE ions with a NIR PL into an inorganic compound does not usually result in the formation of a NIR ML material, which can only be achieved in the combination of Nd³⁺ ions and a CaZnOS compound among the combinations we studied. The newly discovered NIR ML material (CaZnOS:Nd³⁺) is biocompatible and can efficiently convert mechanical stress into NIR light over the first and second tissue-penetrating bioimaging window. Its NIR ML emission appeared at a very low force threshold (even when the material was shaken slightly), increased sensitively and linearly with the increase in the force (up to >5 kN), and could penetrate the tissue as deep as >22 mm to enable biomechanical detection. Such a force-responsive behavior is highly reproducible. Hence, CaZnOS:Nd³⁺ is a new potential ultrasensitive biomechanical probe and expands the ML application horizons into in vivo bioimaging

Tunable Luminescent Properties and Concentration-Dependent, Site-Preferable Distribution of Eu²⁺ Ions in Silicate Glass for White LEDs Applications

The design of luminescent materials with widely and continuously tunable excitation and emission is still a challenge in the field of advanced optical applications. In this paper, we reported a Eu²⁺-doped SiO₂-Li₂O-SrO-Al₂O₃-K₂O-P₂O₅ (abbreviated as SLSAKP:Eu²⁺) silicate luminescent glass. Interestingly, it can give an intense tunable emission from cyan (474 nm) to yellowish-green (538 nm) simply by changing excitation wavelength and adjusting the concentration of Eu²⁺ ions. The absorption spectra, photoluminescence excitation (PLE) and emission (PL) spectra, and decay curves reveal that there are rich and distinguishable local cation sites in SLSAKP glasses and that Eu²⁺ ions show preferable site distribution at different concentrations, which offer the possibility to engineer the local site environment available for Eu²⁺ ions. Luminescent glasses based color and white LED devices were successfully fabricated by combining the as-synthesized glass and a 385 nm n-UV LED or 450 nm blue LED chip, which demonstrates the potential application of the site engineering of luminescent glasses in advanced solid-state lighting in the future

Highly Efficient and Thermally Stable K₃AlF₆:Mn⁴⁺ as a Red Phosphor for Ultra-High-Performance Warm White Light-Emitting Diodes

Following pioneering work, solution-processable Mn⁴⁺-activated fluoride pigments, such as A₂BF₆ (A = Na, K, Rb, Cs; A₂ = Ba, Zn; B = Si, Ge, Ti, Zr, Sn), have attracted considerable attention as highly promising red phosphors for warm white light-emitting diodes (W-LEDs). To date, these fluoride pigments have been synthesized via traditional chemical routes with HF solution. However, in addition to the possible dangers of hypertoxic HF, the uncontrolled precipitation of fluorides and the extensive processing steps produce large morphological variations, resulting in a wide variation in the LED performance of the resulting devices, which hampers their prospects for practical applications. Here, we demonstrate a prototype W-LED with K₃AlF₆:Mn⁴⁺ as the red light component via an efficient and water-processable cation-exchange green route. The prototype already shows an efficient luminous efficacy (LE) beyond 190 lm/W, along with an excellent color rendering index (Ra = 84) and a lower correlated color temperature (CCT = 3665 K). We find that the Mn⁴⁺ ions at the distorted octahedral sites in K₃AlF₆:Mn⁴⁺ can produce a high photoluminescence thermal and color stability, and higher quantum efficiency (QE) (internal QE (IQE) of 88% and external QE (EQE) of 50.6%.) that are in turn responsible for the realization of a high LE by the warm W-LEDs. Our findings indicate that the water-processed K₃AlF₆ may be a highly suitable candidate for fabricating high-performance warm W-LEDs

Luffa-Sponge-Like Glass–TiO₂ Composite Fibers as Efficient Photocatalysts for Environmental Remediation

Structural design of photocatalysts is of great technological importance for practical applications. A rational design of architecture can not only promote the synthetic performance of photocatalysts but also bring convenience in their application procedure. Nanofibers have been established as one of the most ideal architectures of photocatalysts. However, simultaneous optimization of the photocatalytic efficiency, mechanical strength, and thermal/chemical tolerance of nanofibrous photocatalysts remains a big challenge. Here, we demonstrate a novel design of TiO₂–SiO₂ composite fiber as an efficient photocatalyst with excellent synthetic performance. Core–shell mesoporous SiO₂ fiber with high flexibility was employed as the backbone for supporting ultrasmall TiO₂ nanowhiskers of the anatase phase, constructing core@double-shell fiber with luffa-sponge-like appearance. Benefitting from their continuously long fibrous morphology, highly porous structure, and completely inorganic nature, the TiO₂–SiO₂ composite fibers simultaneously possess high photocatalytic reactivity, good flexibility, and excellent thermal and chemical stability. This novel architecture of TiO₂–SiO₂ glass composite fiber may find extensive use in the environment remediation applications

Site Occupation of Eu²⁺ in Ba_2–<i>x</i>Sr_<i>x</i>SiO₄ (<i>x</i> = 0–1.9) and Origin of Improved Luminescence Thermal Stability in the Intermediate Composition

Knowledge of site occupation of activators in phosphors is of essential importance for understanding and tailoring their luminescence properties by modifying the host composition. Relative site preference of Eu²⁺ for the two distinct types of alkaline earth (AE) sites in Ba_{1.9995–<i>x</i>}Sr_<i>x</i>Eu_0.0005SiO₄ (<i>x</i> = 0–1.9) is investigated based on photoluminescence measurements at low temperature. We found that Eu²⁺ prefers to be at the 9-coordinated AE2 site at <i>x</i> = 0, 0.5, and 1.0, while at <i>x</i> = 1.5 and 1.9, it also occupies the 10-coordinated AE1 site with comparable preference, which is verified by density functional theory (DFT) calculations. Moreover, by combining low-temperature measurements of the heat capacity, the host band gap, and the Eu²⁺ 4f⁷ ground level position, the improved thermal stability of Eu²⁺ luminescence in the intermediate composition (<i>x</i> = 1.0) is interpreted as due to an enlarged energy gap between the emitting 5d level and the bottom of the host conduction band (CB), which results in a decreased nonradiative probability of thermal ionization of the 5d electron into the host CB. Radioluminescence properties of the samples under X-ray excitation are finally evaluated, suggesting a great potential scintillator application of the compound in the intermediate composition