Adv. Funct. Mater., 2022, 32, 13, 2110771. https://doi.org/10.1002/adfm.202110771

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.

Inorg. Chem. Front., 2022,9, 1912-1919 https://doi.org/10.1039/D2QI00217E

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.

ACS Appl. Mater. Interfaces 2022, 14, 1, 1496–1504 https://pubs.acs.org/doi/10.1021/acsami.1c21321

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 SrGa_10.49In_1.5O₁₉:0.01Cr³⁺ 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.

Mater. Today Chem. 2022,24 https://doi.org/10.1016/j.mtchem.2022.100806

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.

Int. J. Miner. Metall. Mater., 29(2022), No. 6, pp. 1286-1294. http://ijmmm.ustb.edu.cn/article/doi/10.1007/s12613-021-2363-6

Cr3+-activated far-red and near-infrared phosphors have drawn considerable attention owing to their adjustable emission wavelengths and wide applications. Herein, we reported a series of Cr3+-doped phosphors with β-Ca3(PO4)2-type structure, of which Ca9Ga(PO4)7:Cr3+ possessed the highest far-red emission intensity. At an excitation of 440 nm, the Ca9Ga(PO4)7:Cr3+ phosphors exhibited a broad emission band ranging from 650 to 850 nm and peaking at 735 nm, and the broadband superimposed two sharp lines centering at 690 and 698 nm. The optimal sample Ca9Ga0.97(PO4)7:0.03Cr3+ had an internal quantum efficiency of 55.7%. The luminescence intensity of the Ca9Ga0.97(PO4)7:0.03Cr3+ phosphor obtained at 423 K could maintain 68.5% of that at room temperature, demonstrating its outstanding luminescence thermal stability. A phosphor-conversion light-emitting diode was fabricated, indicating that the Ca9Ga(PO4)7:Cr3+ phosphor has potential applications in indoor plant cultivation.

Sci. China Mater. 65, 748–756 (2022).https://doi.org/10.1007/s40843-021-1785-6

For healthy lighting, daily lighting that considers both visible light and near-infrared (NIR) light is necessary. However, at ∼900 nm, the extensively used solar-like phosphor-converted light-emitting diodes (pc-LEDs) are limited by a lack of high-performance NIR luminescent materials. We report a broadband NIR phosphor Sr₂ScSbO₆:Cr³⁺ with a double perovskite-type structure, thus simultaneously demonstrating high luminescence efficiency and good thermal stability. Under 550-nm excitation, Sr₂ScSbO₆:Cr³⁺ demonstrates broadband NIR emission centered at ∼890nm with luminescence internal/external efficiencies of 82.0%/35.7%, respectively. Furthermore, the luminescence integrated intensity at 430 K remains at ∼66.4% of the initial intensity. We successfully fabricated pc-LED devices using a 465-nm-sized blue chip and other commercial phosphors, presenting a relatively complete solar-like spectrum from blue to NIR light and is expected to be used in solar-like lighting.

Chem. Mater. 2021, 33, 21, 8360–8366 https://pubs.acs.org/doi/10.1021/acs.chemmater.1c02734

Energy transfer (ET) between optically active ions usually leads to luminescent concentration quenching and thermal quenching. Toward luminescence enhancement, it is very challenging to control the ET path. Herein, we demonstrated a strategy for selectively controlling ET pathway through the structural confinement effect for activated ions. In the Yb3+-doped Sr9Cr(PO4)7 (SCP) compound, Cr3+ ions are well separated from each other (≥8.97 Å), but they are close to Yb3+ ions (3.70–5.29 Å) due to structural confinement. Therefore, ET is depressed between Cr3+ ions but induced from Cr3+ to Yb3+ ions. On increasing Yb3+ concentration, the thermal stability of near-infrared emission is significantly improved. The emission intensity of the SCP:0.15Yb3+ phosphor at 375 K can keep 100% of that at 80 K. Finally, we show the potential applications of SCP:Yb3+ phosphor in food analysis and nondestructive examination fields. This study provides a new strategy for enhancing luminescence.

https://doi.org/10.1016/j.mtchem.2021.100704

Searching for broadband near-infrared (NIR) materials with high efficiency and excellent thermal luminescence stability is of great significance because of their widespread spectroscopic applications. Different element substitution can modulate the structure and crystal field of host lattice so as to regulate the luminescent properties. Herein, we report the octahedron-dependent NIR luminescence in Cr3+-doped KMP2O7 (M = Ga, Sc, In, and Lu) phosphors and investigate the effect of octahedral environment on luminescent properties, aiming to provide guidance for host material selection. The decreased crystal field strength leads to the apparent spectral red shift from 815 to 900 nm for the samples of M = Ga to Lu. The small Stokes shift as well as weak electron–phonon coupling effect decreases the non-radiative transition probability and thus gives rise to the highest emission intensity and excellent thermal stability of Cr3+-doped KGaP2O7. The optimal sample, KGa0.89P2O7:0.11Cr3+, possesses an internal/external quantum efficiency of 55.8%/36.6%, and its integrated emission intensity at 423 K can maintain 68% of that at room temperature. Finally, we investigate the potential applications in non-destructive examination field by manufacturing a NIR phosphor-conversion light-emitting diode device.