Dalton Trans., 2023,52, 9368-9376, https://doi.org/10.1039/D3DT01209C

Mixing cations with different chemical properties to induce the generation of asymmetric structures is a new approach for tuning the optical properties of hybrid organic–inorganic metal halides (HOIMHs). In this study, zero-dimensional (C₉N₃H₁₅)(C₉H₁₃SO)MBr₆ (M = Bi/Sb, [C₉N₃H₁₅]²⁺ = [(C₄N₂H₁₀)(C₅NH₅)]²⁺ and [C₉H₁₄SO]⁺ = [CH₃(C₆H₄)OS(CH₃)₂]⁺) are synthesized. Two different cations cause both compounds to crystallize in the polar space group P2₁2₁2₁, thus resulting in significant phase matchable second harmonic generation under a 1064 nm laser excitation. Thus, (C₉N₃H₁₅)(C₉H₁₃SO)BiBr₆ and (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibit intensities that are approximately 1.8 and 1.7 times that of KH₂PO₄, respectively. The results of density functional theory calculations show that both (C₉N₃H₁₅)(C₉H₁₃SO)BiBr₆ and (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibit direct bandgaps of 2.95 and 2.81 eV, respectively. Additionally, because of the distortion of the inorganic octahedra, (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibited bright yellow emission at room temperature, which is attributed to ns² fluorescence emission. We believe that the symmetry of the HOIMH crystal structure can be broken by introducing spatially differentiated bifunctional organic cations, which consequently enables even-order nonlinear activities.

J. Mater. Chem. C, 2023,11, 48-96, https://doi.org/10.1039/D2TC02639B

Ce³⁺/Eu²⁺ activated luminescent materials offer a versatile platform for precise emission light manipulation through structure control on the basis of the composition–structure–property correlations. To date, Ce³⁺/Eu²⁺ activated phosphors have been well developed as an indispensable component in the lighting industry and display systems due to their superior performance. Meanwhile, many persistent phosphors contain Ce³⁺/Eu²⁺ together with other lanthanide or transition-metal co-dopants. It is therefore of great importance to focus on their similarities and gain insight into the interplay effect of the local structure and electronic structure on emission peak modulation and persistent duration elongation. Here, we review the theoretical and experimental progress in the discovery and optimization of Ce³⁺/Eu²⁺ activated LEDs and persistent phosphors. The Dorenbos model on f–d transitions and the latest developments in the correlation of the local structure and luminescence characteristics are elaborated to give an overall vision on the composition–structure–property correlations in Ce³⁺/Eu²⁺-activated phosphors. Particular attention is devoted to highlighting the critical role of the electronic structure in tuning the properties of phosphors. The development and optimization routines of some typical phosphors are expounded, with an emphasis on phosphor design principles, aiming at providing inspirations for tailoring and optimizing the properties of Ce³⁺/Eu²⁺-activated phosphors toward specific applications. Finally, we propose an outlook toward potential theory developments and future material discovery.

J. Mater. Chem. C, 2023,11, 8196-8203, https://doi.org/10.1039/D2TC05554F

Hybridized local and charge-transfer (HLCT) emitters are promising for the realization of high-performance blue organic light-emitting diodes (OLEDs). However, the rational design of efficient HLCT emitters remains challenging. Here, we present two blue emitters (TAP1 and TAP2) with the HLCT state through the construction of D–π–A molecules. Theoretical calculations reveal the large overlap and partial separation of “hole” and “particle” orbitals for S₁ excited states, demonstrating the HLCT nature of the emitters. Together with the clear solvatochromic phenomenon, we propose that introducing the π-conjugated anthracene unit into an appropriate donor–acceptor segment is an effective strategy to finely regulate the locally excited and charge transfer components and construct versatile HLCT emitters. Employing TAP2 and TAP1 as emitters, the blue OLEDs exhibit good color purity, high efficiency, and extremely low efficiency roll-offs with Commission internationale de l’éclairage coordinates of, respectively, (0.14, 0.10) and (0.15, 0.11), narrow full width at half maximum values of 45 nm and 52 nm, maximum external quantum efficiency values of 5.53% and 5.16%, and efficiency roll-off values of 0.5% and 1% at the practical brightness of 1000 cd m⁻². By virtue of the transient photoluminescence decay curves, excited state energy levels and natural transition orbital analysis, we classify that the reverse intersystem crossing at high-lying excited states from T₂ to S₁ serves as an efficient approach to harvest triplet excitons and thus boost the exciton utilization efficiency. The superior properties of HLCT emitters in this work provide inspiration for the rational design of promising materials for high-performance blue OLEDs.

Dalton Trans., 2023,52, 5119-5126, https://doi.org/10.1039/D2DT04067K

Organic–inorganic hybrid metal halides have been extensively studied because of their great potential in optoelectronics. Herein, we report three hybrid metal halides (Bmpip)₂ZnBr₄, (Bmpip)₂CdBr₄, and (Bmpip)₈Pb₁₁Br₃₀ (where Bmpip⁺ is 1-butyl-1-methyl-piperidinium, C₁₀H₂₂N⁺). (Bmpip)₂ZnBr₄ and (Bmpip)₂CdBr₄ crystallize in the P2₁/c space group with zero-dimensional crystal structures with [MBr₄]²⁻ (M = Zn, Cd) tetrahedra isolated by Bmpip⁺. (Bmpip)₈Pb₁₁Br₃₀ crystallizes in the triclinic space group P

 with one-dimensional corrugated chains constructed from face-sharing [PbBr₆]⁴⁻ octahedra. All of the compounds exhibit excellent ambient and thermal stability. Under UV excitation, all three compounds exhibit very broad emissions. Temperature-dependent photoluminescence measurements indicate that the broad emissions of (Bmpip)₂ZnBr₄ and (Bmpip)₂CdBr₄ can be attributed to both the organic cations and self-trapped excitons (STEs) and that the emission of (Bmpip)₈Pb₁₁Br₃₀ is assigned to STEs. Density functional theory calculations reveal that the three compounds adopt a direct band gap. This work enriches our understanding of the structure types of hybrid metal halides while revealing their diverse emission mechanisms.

J. Mater. Chem. C, 2023,11, 8462-8469, https://doi.org/10.1039/D3TC00528C

An efficient Cr³⁺-activated broadband near-infrared (NIR) phosphor is the key enabler to integrate compact NIR light-emitting diodes (pc-LEDs) for food testing and medical detection applications. High luminescence efficiency is key for the practical applications of phosphors. Herein, we design a series of efficient Cr³⁺-doped Ca₃Al_2−ySc_yGe₃O₁₂ garnet phosphors to induce octahedral distortion for enhancing NIR luminescence efficiency. We adopt the best fitted ideal polyhedron to characterize the octahedral distortion and found that the degree of distortion reaches its maximum at y = 0.2 and decreases with y deviating from 0.2. As a result, the composition with y = 0.2 shows the highest luminescence intensity. The composition dependence of the octahedral distortion coincides with that of the luminescence intensity, indicating that the luminescence properties of Ca₃Al_2−ySc_yGe₃O₁₂:Cr³⁺ are closely related to the octahedral distortion. The luminescence internal/external quantum efficiency (IQE/EQE) is significantly enhanced from 65.4%/25.7% in Ca₃Al₂Ge₃O₁₂:0.04Cr³⁺ to 85.4%/33.5% in Ca₃Al_1.8Sc_0.2Ge₃O₁₂:0.04Cr³⁺. The optimal Ca₃Al_1.8Sc_0.2Ge₃O₁₂:0.04Cr³⁺ phosphor exhibits excellent luminescence thermal stability (∼91% at 423 K) and high NIR output power (38.2 mW at 100 mA) with an electro-optical conversion efficiency of 13.7%. This work provides a strategy for enhancing the NIR luminescence of Cr³⁺.

Inorg. Chem. Front., 2023,10, 2430-2437, https://doi.org/10.1039/D2QI02489F

With the pursuit of healthy lighting, full-spectrum white light-emitting diodes (WLEDs) fabricated with violet chips and tri-color phosphors have been put forward. However, the excitation bands of most reported blue phosphors are located in the ultraviolet (UV) region, which hinders the development of full-spectrum lighting. In this work, by partially introducing N³⁻ into a matrix, a series of Ba_0.697Al_10.914O_17.232-3y/2N_y:0.16Eu²⁺ (BAON_y:Eu) blue phosphors with red-shifted photoluminescence excitation (PLE) spectra were synthesized. Under the excitation of 400 nm violet light, the internal/external quantum efficiency (IQE/EQE) values of the optimal sample BAON_1.0:Eu were calculated to be 80%/52%, while the retained integrated emission intensity at 150 °C can be 95% of that at room temperature. The WLED device fabricated by coating BAON_1.0:Eu and other commercial phosphors on a violet chip achieved an ultra-high color rendering index (R_a = 95.4). These results indicate that our synthesized BAON_1.0:Eu can be an excellent candidate blue phosphor for full-spectrum WLED lighting.

Inorg. Chem. 2023, 62, 31, 12501–12509.https://doi.org/10.1021/acs.inorgchem.3c01726

Organic–inorganic metal halides (OIMHs) have various crystal structures and offer excellent semiconducting properties. Here, we report three novel OIMHs, (PPA)₆InBr₉ (PPA = [C₆H₅(CH₂)₃NH₃]⁺), (PBA)₂SbBr₅, and (PBA)₂SbI₆ (PBA = [C₆H₅(CH₂)₄NH₃]⁺), showing typical zero-dimensional (0D) structure, octahedra dimers, and corner-sharing one-dimensional chains and crystallized in the monoclinic system with P2₁, P2₁/c, and C2/c space groups, respectively. (PPA)₆InBr₉, (PBA)₂SbBr₅, and (PBA)₂SbI₆ have experimental optical band gaps of ∼3.16, ∼2.24, and 1.48 eV, respectively. (PPA)₆InBr₉ exhibits bright-orange light emission centered at 642 nm with a full-width at half-maximum of 179 nm (0.51 eV) and a Stokes shift of 277 nm (1.46 eV). After Sb³⁺ doping, the peak position did not change, and the photoluminescence quantum yield increased significantly from 9.2 to 53.0%. The efficient emission of Sb:(PPA)₆InBr₉ stems from the isolated ns² luminescent center and strong electron–phonon coupling, making the spin-forbidden ³P₁–¹S₀ observable. By combining commercial blue and green phosphors with orange-red-light-emitting (PPA)₆In_0.99Sb_0.01Br₉, a white-light-emitting diode was constructed, with the color-rendering index reaching up to 92.3. Our work highlights three novel 0D OIMHs, with chemical doping of Sb³⁺ shown to significantly enhance the luminescence properties, demonstrating their potential applications in solid-state lighting.

Journal of Alloys and Compounds Volume 960, 15 October 2023, 170895, https://doi.org/10.1016/j.jallcom.2023.170895

Pavonite homologues are semiconductors that show potential for thermoelectric applications. Herein, we report the synthesis of a quaternary selenide, In_0.5Mn₂Bi_3.5Se₈, that exhibits good thermal stability below 1032 K. Whereas most pavonite compounds exhibit the metallic properties of degenerate semiconductors, In_0.45Mn_2.17Bi_3.38Se₈ possesses a band gap of 0.85 eV. In addition, its electrical conductivity and Seebeck coefficient exceed 3 S/cm and 300 μV/K at 810 K, respectively, with the compound mainly displaying semiconductor properties. In_0.45Mn_2.17Bi_3.38Se₈ exhibits paramagnetism at room temperature followed by a paramagnetic-to-antiferromagnetic transition at ∼10.2 K. Our findings enrich the current understanding of the pavonite homologous series, providing useful insight for future exploration in related fields.

ADVANCED OPTICAL MATERIALS, 2023-02-04, https://doi.org/10.1002/adom.202202304

Efficient broadband emitting organic–inorganic metal hybrids (OIMHs) have attracted great attention recently as promising single-component white light emitters. Here a new zero-dimensional (0D) OIMH (C₁₃H₁₄N)₂InCl₅ (C₁₃H₁₄N⁺ = N-methyldiphenylammonium) is reported, which features unique five-coordinated [InCl₅]²⁻ trigonal bipyramid motif. For the first time, it is demonstrated that the trigonal bipyramid units in 0D OIMH can act as luminescence centers, showing blue emission under UV light. Remarkably, incorporating Sb³⁺ in [InCl₅]²⁻ trigonal bipyramids induces a new dual-band emission at 540 and 735 nm resulting from the singlet and triplet self-trapped excitons in [SbCl₅]²⁻, leading to complete coverage of the entire visible spectrum. The resulting emissions in (C₁₃H₁₄N)₂InCl₅:Sb³⁺ are tunable from cold to warm white with the correlated color temperatures changing from 5574 to 3473 K and more importantly, an ultra-high color rendering index (CRI) up to 96 being observed, which is comparable to the highest value in hybrid metal halides. A high photoluminescence quantum yield of 46.26% is simultaneously obtained in this system. This work demonstrates that the 0D OIMH with trigonal bipyramid motif is an excellent system for realizing the single-component white light emission with both high efficiency and ultra-high CRI.