Stimulus-responsive photoluminescent materials have attracted extensive research attention in recent years owing to their potential application in information storage and switch devices. It is important to further explore such bistable materials as well as the underlying transformation mechanisms. Herein, the syntheses and mechanically tunable “on–off” photoluminescence (PL) of two organic–inorganic hybrid metal halides, (Bmpip)9Pb3Zn2Br19 and (Bmpip)9Pb3Cd2Br19 (Bmpip+ = 1-butyl-1-methyl-piperidinium, C10H22N+), are reported. Both as-obtained compounds are nonemissive under UV light at ambient conditions but exhibit bright PL upon grinding or under hydrostatic pressure. Interestingly, the PL is quenchable by short-time annealing or storage in air for 1 week, and the process is repeatable. Through a combination of extensive structural and spectral analyses, the crucial role of the organic cations interacting with inorganic chromophores in the “on–off” PL behavior of the title compounds is revealed. Moreover, pressure-induced PL and PL-enhancement phenomena are observed in both compounds, which are similar to but slightly different than the above-mentioned mechano-PL. Finally, proof-of-concept devices are fabricated to demonstrate the potential applications of the title compounds in message recording and force sensing.
Organic–inorganic metal halides (OIMHs) exhibit excellent photoelectric properties; however, their high-temperature light-emission stability requires further improvement. Here, we report three isostructural OIMHs (C2H8N)4InCl7, (C2H8N)4SbCl7, and (C2H8N)4SbBr7 (C2H8N+ = dimethylammonium). They are all crystallized in the P21212 space group with a zero-dimensional (0D) structure, with orange-red photoluminescence (PL) under 365 nm UV excitation. Among them, (C2H8N)4InCl7 exhibits the strongest PL with a photoluminescence quantum yield (PLQY) of 13.9% at room temperature. Optical property measurements and density functional theory unveil that the luminescence of (C2H8N)4InCl7 at 405 and 620 nm is due to free exciton and self-trapped exciton emission, respectively. It is worth noting that (C2H8N)4InCl7 shows a high PL quenching temperature, maintaining 50% of its room-temperature PL intensity at 425 K, which is rare in OIHMs. This is much higher than the application temperature of phosphors in practical solid-state lighting applications (363–383 K). In this temperature range, the luminous intensity of (C2H8N)4InCl7 exceeds 60% of that at room temperature. The high PL quenching temperature observed in (C2H8N)4InCl7 indicates the potential of OIMHs for applications in phosphor-converted light-emitting diodes.
Broadband near-infrared (NIR) emitting phosphors have attracted great interest due to their potential applications in non-destructive examination and bioimaging. However, most of the reported broadband NIR phosphors emit in the NIR-I region with a wavelength shorter than 950 nm, while rare-earth activated NIR-II phosphors can hardly meet the requirements because of their sharp emission. Herein, we successfully synthesized the broadband NIR-II phosphor Li2ZnGeO4:Cr4+. By employing the all-tetrahedron-built matrix, all the Cr ions are stabilized in the tetravalent state due to crystallographic control. This phosphor shows wide absorption from the red to near-infrared region. Under 646 nm excitation, it exhibits broadband NIR-II emission peaking at 1218 nm with an FWHM of 220 nm at room temperature. We also demonstrated the potential applications of Li2ZnGeO4:Cr4+ as an NIR-II light source in non-destructive examination and bioimaging. This work provides a new strategy for exploring broad-band NIR-II luminescent materials.
Near-infrared (NIR)-persistent luminescence (PersL) materials are of promising applications in labeling, tracing, bio-imaging, and so forth, featuring distinctive self-sustained NIR light emitting. The PersL radiation spectrum, PersL duration, and charging efficiency are recognized as the key enablers for high-performance NIR PersL materials. Here, we have designed and developed a series of broad-band NIR superlong PersL phosphors (Sr,Ba) (Ga,In)12O19:Cr3+ with efficient UV-red light charging capacity. Typical SrGa10.49In1.5O19:0.01Cr3+ presents intensive NIR PersL from 650 to 1000 nm peaking at ∼770 nm, with a PersL duration of 360 h. This material can be efficiently and repeatedly charged by solar radiation in various outdoor environments. Our work further identifies that this NIR PersL material is advantageous for labeling and tracing as a secret NIR additive and in situ bio-imaging as an optical probe under high tissue penetration red light excitation.
Materials with the ability to persistently emit intense near-infrared (NIR) light after ceasing excitation are very useful in many fields. The persistent time is a vital parameter for successful applications. In this study, we developed an emerging NIR super-long persistent luminescent (PersL) material, Cr3+-activated magnetoplumbite oxide La(Zn/Mg)(Ga,Al)11O19:Cr3+, by doping Yb3+ as a new efficient electron trap and incorporating Al3+ to engineer the energy band. We show that fine control of the trap depth and density is the key underpinning for PersL enhancement. The title material emits intense PersL in the spectral range of 600–950 nm with a PersL time of more than 1,000 h. Furthermore, after undergoing such long-term decay, the NIR emission can be revived by photo-/thermo-stimulation. We demonstrate its potential uses in bioimaging, multilevel anti-counterfeiting, tracing, and positioning. This study provides insight into how energy band engineering manipulates electronic structures to achieve high-performance PersL. The new NIR persistent phosphor may be soon utilized in related applications.
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