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.

J. Mater. Chem. C, 2022,10, 9841-9848.https://doi.org/10.1039/D2TC01672A

As an emerging material, organic–inorganic metal halides (OIMHs) have been widely studied in the field of optoelectronics in recent years. In this work, a series of compounds (TMEDA)₃(Sb_xBi_1−x)₂Cl₁₂·H₂O (0.1 ≤ x ≤ 0.6) (TMEDA = N,N,N′-trimethylethylenediamine) were synthesized. The incorporation of Sb³⁺ greatly enhanced the photoluminescence quantum yield of (TMEDA)₃Bi₂Cl₁₂·H₂O from 1% to 38%. The variation in the degree of distortion of the inorganic octahedra and the relatively suitable distances between metal ions are considered to be the reasons for the intense emission. (TMEDA)₃(Sb_xBi_1−x)₂Cl₁₂·H₂O (0.1 ≤ x ≤ 0.6) exhibited a yellow phosphorescence emission at 605 nm and 595 nm under excitation at 305 nm and 375 nm, respectively. With the incorporation of Sb³⁺, changes in the emission intensity under different excitation wavelengths showed different trends. Thus, we attribute the yellow broadband emissions to the triplet emission of Bi³⁺ and Sb³⁺. Finally, we combined (TMEDA)₃(Sb_0.5Bi_0.5)₂Cl₁₂·H₂O with commercial phosphors and a near-ultraviolet light-emitting diode chip to prepare a white-light-emitting diode device, which exhibited a high color-rendering index of 94.4. The aim of our work was to investigate the structural effects of the photoluminescence of Sb³⁺-doped OIMHs and to further explore ways to improve the Sb³⁺ emission efficiency in the field of photoluminescence of OIMHs.

J. Mater. Chem. C, 2022,10, 13137-13142.https://doi.org/10.1039/D2TC02838G

Low-dimensional organic–inorganic metal halides with broad light emission have drawn widespread attention, however, the low thermal stability has been a major obstacle to their commercialization. Herein, zero-dimensional (C₉H₁₅N₃)ZnCl₄ with space group P2₁ was synthesized for the first time. (C₉H₁₅N₃)ZnCl₄ emits blue fluorescence at room temperature with external quantum efficiency as high as 42.5%, which are among the highest reported for Zn-based OIMHs, and it is comparable with the commercialized phosphors. Notably, the luminous integral intensity of (C₉H₁₅N₃)ZnCl₄ at 470 K remains more than 50% of that at room temperature. Mn²⁺ doping of (C₉H₁₅N₃)ZnCl₄ was conducted to improve the photoluminescence. With increasing Mn²⁺ concentration, the title compounds underwent fluorescence conversion from blue to green. The external quantum efficiencies of (C₉H₁₅N₃)ZnCl₄ : 5%Mn²⁺ and (C₉H₁₅N₃)ZnCl₄ : 50%Mn²⁺ were 43.7% and 42.9%, respectively. More importantly, (C₉H₁₅N₃)ZnCl₄ : 5%Mn²⁺ exhibited different luminous colors at different temperatures. As the temperature decreased from 290 to 110 K, the luminous color changed from green to light blue. Finally, a composite film was prepared to demonstrate the temperature response of this material, and the absolute sensitivity reaches 0.57%/K. These findings fill in the gaps for low-temperature indication and expand the application scenarios of OIMHs.

ACS Appl. Electron. Mater. 2022, 4, 4068−4076.https://doi.org/10.1021/acsaelm.2c00705

Phosphors with narrow-band emission are in great demand for liquid crystal display backlighting applications. In this work, four zero-dimensional Mn²⁺-based organic–inorganic metal halides (OIMHs), (C₁₃H₂₆N)₃MnBr₄·Br, (C₁₃H₂₆N)₂MnCl₄, and (C₇H₁₈N)₂MnX₄ (X = Cl, Br), were synthesized, and their crystal structures were solved. Under blue-light excitation, all of the materials exhibited bright narrow-band green luminescence centered at 515–525 nm with high photoluminescence quantum yields (PLQYs). Significantly, (C₁₃H₂₆N)₃MnBr₄·Br and (C₁₃H₂₆N)₂MnCl₄ exhibited small full width at half-maximum (FWHM) values of 43 and 48 nm with PLQYs of 77.8 and 79.3% at room temperature, respectively. Compared with the reported luminescent OIMHs, ultrahigh thermal quenching temperatures were observed, and at 420 K, emission intensities of (C₁₃H₂₆N)₃MnBr₄·Br and (C₁₃H₂₆N)₂MnCl₄, remained 82.7 and 64.2% of those at room temperature, respectively. The rigid environment provided by the C₁₃H₂₆N⁺ cation has a strong confinement effect on the [MnX₄]^2– tetrahedra, leading to a narrower FWHM and higher thermal quenching temperature. Finally, (C₁₃H₂₆N)₃MnBr₄·Br was combined with commercial phosphors to fabricate light-emitting diodes (LEDs) with a wide color gamut of up to 113% NTSC (National Television System Committee). This work provides a reference for designing the OIMHs for liquid crystal display LEDs by tuning the organic cations.