LASER & PHOTONICS REVIEWS.08 February 2023.https://doi.org/10.1002/lpor.202200999

For the conventional persistent luminescence (PersL) charging processes, carriers are photo-pumped to the conduction band (CB) or high-energy excited states (HES) under short-wavelength UV or coherent near-infrared (NIR) laser excitation. Herein, electron tunneling charging behavior is reported in Cr³⁺, Sm³⁺ co-doped NIR PersL magnetoplumbite SrGa₁₂O₁₉, which allows for efficient charging by incoherent visible light. First, the electrons are efficiently captured by the neighboring Ga^II-O²⁻ electron–hole trap centers via a tunneling process, and then these excited electrons are transferred to shallow traps via a persistently energetic optical pump. This work further optimizes the PersL performance via engineering the energy band through partial substitution of In³⁺ for Ga³⁺. Consequently, tunneling charging occurring near the neighboring Cr³⁺-traps dimers enables Sr(Ga,In)₁₂O₁₉:Cr³⁺,Sm³⁺ to display brighter NIR PersL (≈760 nm, peak; ≈100 nm, FWHM) than gallate spinel under sunlight irradiation. This work provides insights into electron tunneling charging under low-energy excitation for NIR PersL, which may inspire more PersL explorations for practical applications.

ADVANCED OPTICAL MATERIALS.27 April 2023.https://doi.org/10.1002/adom.202300218

Organic–inorganic metal halides (OIMHs) with high-efficiency solar spectrum-like emission are attracting broad and current interest. Here, five 0D Zn-based hybrid halides are synthesized based on aromatic organic cations with different carbon-chain lengths: C₆H₅CH₂NH₃⁺ (PMA⁺) and C₆H₅(CH₂)₄NH₃⁺ (PBA⁺). (PMA)₂ZnCl₄ exhibits the highest photoluminescence quantum yield of 37.2% of reported Zn-based white-emission OIMHs. The emission spectrum of (PBA)₂ZnI₄ indicates a color rendering index of 98, which is the highest among single-component white-light-emitting phosphors. Spectral characterizations and density functional theory calculations demonstrate that the extremely broad emission of (PBA)₂ZnI₄ originates from the synergistic emission of organic cations and self-trapped excitons. The optical properties of the obtained (PMA)₂ZnBr₄, (PMA)₂ZnI₄·H₂O, and (PBA)₂ZnCl₄ are also characterized for comparison, and with the same organic cations, the PLQY decreases from chloride to bromide to iodide. This work demonstrates that the selection of appropriate organics and halogens can enable fine tuning of single-component white-light emission, satisfying varying needs for solid-state lighting.

Inorg. Chem. 2022, 61, 19, 7560–7567.https://doi.org/10.1021/acs.inorgchem.2c00711

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.

Inorg. Chem. Front., 2022,9, 3865-3873.https://doi.org/10.1039/D2QI00884J

Lead-based organic–inorganic metal halides (OIMHs) have recently attracted special attention due to their efficient broadband photoluminescence. However, the toxicity of lead poses a challenge for their further development. Here, we selected Sn(IV) as the metal center to synthesize the environmentally friendly and stable luminescent OIMHs (C₉H₁₅N₃)₂SnCl₈ and (C₉H₁₅N₃)₂SnBr₈ (C₉H₁₃N₃ is 1-(2-pyridyl)piperazine). Both compounds possess zero-dimensional structures, crystallizing in the monoclinic space group P2₁/c, and their optical band gaps were experimentally determined to be 3.19 and 2.60 eV, respectively. Under UV excitation at room temperature, (C₉H₁₅N₃)₂SnCl₈ exhibited double-peak emissions centered at 405 and 688 nm, which were attributed to the organic cation and inorganic octahedra, respectively. Upon introducing 5s²-lone-pair-containing Sb³⁺ in (C₉H₁₅N₃)₂SnCl₈, self-trapped emission was promoted, and the photoluminescence quantum yield increased from ∼1% to ∼17.84%. This work suggests effective strategies for finding environmentally friendly stable OIMHs and for further enhancing the luminescence properties through lone-pair-containing cation doping.

Inorg. Chem. 2022, 61, 38, 15016–15022,https://doi.org/10.1021/acs.inorgchem.2c01900

Recently, excellent optical properties of low-dimensional organic–inorganic metal halides, stemming from their tunable structure and optoelectronic properties, have been demonstrated. The synthetic method is critical because it is highly related to the structure and properties of the halide. Herein, we obtain two different antimony bromides, (Bmpip)₂SbBr₅ and (Bmpip)₃Sb₂Br₉, which both possess the P2₁/c space group having different crystal structures, and this confirms the important influence of synthesis on the single-crystal structure. (Bmpip)₂SbBr₅ contains Bmpip⁺ and [SbBr₅]^2– pyramids, and (Bmpip)₃Sb₂Br₉ consists of Bmpip⁺ and Sb-based dimers [Sb₂Br₉]^3–. Under 400 nm excitation, (Bmpip)₂SbBr₅ exhibits a 640 nm orange emission with a quantum yield of ∼11.5% owing to Sb 5s² electron luminescence. A diode was fabricated by (Bmpip)₂SbBr₅ and commercial phosphors and showed a high color render index of 92. Our work reveals the effect of the preparation method on the crystal structure. A luminescent material was finally identified.

Inorg. Chem. 2022, 61, 30, 11973–11980.https://doi.org/10.1021/acs.inorgchem.2c01730

The participation of organic cations plays an important role in tuning broad-spectra emissions. Herein, we synthesized a series of Mn(II)-based two-dimensional (2D) halide perovskites with arylamine cations of different lengths having the general formula (C₆H₅(CH₂)_xNH₃)₂MnCl₄ (x = 1–4), with the x = 4 compound reported here for the first time. With the increase in the −(CH₂)– in organic cations, the distance between adjacent inorganic layers increases, causing the title compounds to exhibit different structural distortions. As the Mn–Cl–Mn angular distortion increases, the experimental optical band gaps of the title compounds increase correspondingly. When the angle distortion between the octahedrons of the compounds is similar, the band gaps may also be affected by the distortion of the octahedron itself (the bond-length distortion of 2 is greater than that of 4). Under UV-light irradiation at 298 K, all of the compounds exhibit two emission peaks centered at 480–505 and 610 nm, corresponding to the organic-cation emission and the ⁴T₁(G) to ⁶A₁(S) radiative transition of Mn²⁺ ions, respectively. Among these title compounds, (PPA)₂MnCl₄ [(PPA)⁺ = C₆H₅(CH₂)₃NH₃⁺] exhibits the strongest photoluminescence (PL). The study of the title compounds contributes to an in-depth understanding of the relationship between the structural distortion and optical properties of 2D Mn(II)-based perovskite materials.

Advanced Functional Materials, 2023, 01, https://doi.org/10.1002/adfm.202209275

Mechanoluminescence (ML), as an optical response to deformation stimuli, shows great potential in high-end stress sensing, ultrasonic field visualization, and multidimensional anti-counterfeiting. However, processive practical applications in bio-medicine are constrained by the discovery of near-infrared (NIR) ML materials. Unlike lanthanides (Ln³⁺) with sharp multiplets, two kinds of Cr³⁺-doped NIR ML materials, gallate spinel (ZnGa₂O₄:Cr³⁺, Zn₃Ga₂GeO₈:Cr³⁺) and gallate magnetoplumbite (SrGa₁₂O₁₉:Cr³⁺) are here reported. Owing to the intrinsic cation antisite defects and cation vacancies in the matrix, these materials exhibit bright NIR ML under a relatively low load (20 N). In particular for SrGa₁₂O₁₉:Cr³⁺ (750 nm, peak; 100 nm, FWHM) with low persistent luminescence (PersL) interference, the ML behavior can be further rejuvenated under UV and sunlight irradiation. SrGa₁₂O₁₉:Cr³⁺ also shows bright NIR emission under photo- and thermo-stimulation. Owing to their excellent tissue penetration and concealment capability, NIR ML materials show great potential in the fields of bio-medicine and anti-counterfeiting.

Inorg. Chem. 2023, 02, 07, 3018–3025, https://doi.org/10.1021/acs.inorgchem.2c03653

Zero-dimensional (0D) In-based organic–inorganic metal halides (OIMHs) have received growing interest in recent years as promising luminescent materials. However, the high efficiencies of 0D In-based OIMHs are all dependent on Sb doping in the existing literature. Here, we report a novel 0D In-based OIMH (C₁₀H₂₂N₂)₂In₂Br₁₀, which exhibits intrinsic broadband emission (610 nm), and the photoluminescence quantum yield (PLQY) can reach 70% without Sb doping. (C₁₀H₂₂N₂)₂In₂Br₁₀ shows a typical 0D structure with three different In–Br polyhedra (two octahedra and one tetrahedron) separated by large organic cations. Based on the optical property measurements and theoretical calculations, we demonstrate that (C₁₀H₂₂N₂)₂In₂Br₁₀ is an indirect semiconductor with a band gap of 3.74 eV, and the In–Br inorganic moiety is primarily responsible for the intense emission of (C₁₀H₂₂N₂)₂In₂Br₁₀. Interestingly, the unique double octahedral configuration in (C₁₀H₂₂N₂)₂In₂Br₁₀ may enhance the structural distortion and stimulate the self-trapped excitons (STEs), leading to the related high PLQY. Our work provides a novel 0D In-based OIMH with high-efficiency intrinsic emission, which is helpful for understanding the structure–PL relationships of hybrid halides.

Laser & Photonics Reviews 2023, 02, 08, https://doi.org/10.1002/lpor.202200999

For the conventional persistent luminescence (PersL) charging processes, carriers are photo-pumped to the conduction band (CB) or high-energy excited states (HES) under short-wavelength UV or coherent near-infrared (NIR) laser excitation. Herein, electron tunneling charging behavior is reported in Cr³⁺, Sm³⁺ co-doped NIR PersL magnetoplumbite SrGa₁₂O₁₉, which allows for efficient charging by incoherent visible light. First, the electrons are efficiently captured by the neighboring Ga^II-O²⁻ electron–hole trap centers via a tunneling process, and then these excited electrons are transferred to shallow traps via a persistently energetic optical pump. This work further optimizes the PersL performance via engineering the energy band through partial substitution of In³⁺ for Ga³⁺. Consequently, tunneling charging occurring near the neighboring Cr³⁺-traps dimers enables Sr(Ga,In)₁₂O₁₉:Cr³⁺,Sm³⁺ to display brighter NIR PersL (≈760 nm, peak; ≈100 nm, FWHM) than gallate spinel under sunlight irradiation. This work provides insights into electron tunneling charging under low-energy excitation for NIR PersL, which may inspire more PersL explorations for practical applications.

J. Appl. Cryst. (2023). 56, 884-888, https://doi.org/10.1107/S160057672300328X

Polyhedron ligands have been frequently used to characterize the ligand environment in inorganic materials. With a cation or anion as the central atom, its bonded counterparts are set as the vertices of the polyhedron. Generally, a series of geometrical parameters of the polyhedron, such as the average bond length and volumetric size, are extracted to illustrate the subtle change of local structure on compositional substitution. Polyhedral distortion analysis is widely adopted in research fields relying on a strong structure–property relationship. For example, in rare-earth or transition-metal element doped luminescent materials, the energy levels of the excited d electrons are highly dependent on the polyhedral distortion of the ligand. As a result, the spectral excitation/emission peaks of the luminescence center can be modulated by composition substitution, which usually induces polyhedral distortion due to the mismatch between ionic radii (Wang et al., 2016; Chen et al., 2017; Zhao et al., 2022). Therefore, characterization of polyhedral distortion constitutes an important part in the crystal structure analysis of inorganic materials.