Electron Tunneling Charging upon Sunlight for Near-Infrared Persistent Luminescence

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 GaII-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.

Efficient Solar Spectrum-Like White-Light Emission in Zinc-Based Zero-Dimensional Hybrid Metal Halides

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.

Small Organic Molecular-Based Hybrid Halides with High Photoluminescence Quenching Temperature

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.

Antimony doping to enhance luminescence of tin(iv)-based hybrid metal halides

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.

Synthetic-Method-Dependent Antimony Bromides and Their Photoluminescent Properties

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.

Photoluminescent Properties of Two-Dimensional Manganese(II)- Based Perovskites with Different-Length Arylamine Cations

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.

Zero-Dimensional Halides with ns2 Electron (Sb3+) Activation to Generate Broad Photoluminescence

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 P21P21/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 3P11S0 observable. By combining commercial blue and green phosphors with orange-red-light-emitting (PPA)6In0.99Sb0.01Br9, 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.

Antimony and bismuth cooperation to enhance the broad yellow photoluminescence of zero-dimensional hybrid halide


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(SbxBi1−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(SbxBi1−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(Sb0.5Bi0.5)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.

Thermal stable zinc-based hybrid halides with high external quantum efficiency as temperature detectors

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.

Efficient Narrow-Band Green Light-Emitting Hybrid Halides for Wide Color Gamut Display

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.