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Understanding the luminescence mechanics of metal halide perovskites is the key to uncovering the detailed pathways responsible for remarkable photophysical properties and engineering materials with enhanced optoelectronic properties. In this work, high pressure is employed to reveal the self‐trapped exciton (STE) emission features of a 1D lead bromide perovskitoid (HM)Pb2Br6. Upon compression, a remarkable 42‐fold enhancement in the intensity compared to the initial emission, along with exciton transfer from STE emission to narrow free exciton emission, is achieved in (HM)Pb2Br6. These phenomena are related to the anisotropic compression of (HM)Pb2Br6, which results in enhanced structural stiffness and a significant reduction in the distances of Pb─Pb bond lengths between inter‐[Pb2Br6]2− chains, as well as Pb─Br bond lengths within the three basic intra‐[Pb2Br6]2− octahedra. These results provide essential insights into the intriguing photophysics of STEs and shed new light on the dramatic exciton transfer to control and enhance the optical properties of the metal halide perovskites. [ABSTRACT FROM AUTHOR]

The inherent structural flexibility and chiroptical activity of 2D chiral perovskites make them promising for the nonlinear optical (NLO) application. A comprehensive understanding of the second‐harmonic generation (SHG) mechanism in 2D chiral perovskites is essential for developing NLO devices. However, the rational design of 2D chiral perovskite structures to regulate SHG properties remains challenging. Herein, to regulate SHG response, an achiral organic spacer cation alloying strategy is employed to construct a series of 2D chiral perovskites. Through the measurement of temperature‐dependent photoluminescence (PL) spectra, it is revealed that the material design strategy can effectively modulating self‐trapped exciton (STE) emission. More importantly, it is confirmed that there is a competitive relationship between STE emission and SHG in 2D chiral perovskites. Meanwhile, the microscopic imaging of circularly polarized‐SHG is demonstrated in chiral perovskites. This work will not only advance the understanding of the SHG mechanism in 2D chiral perovskites but also provide inspiration for the rational design and synthesis of perovskites for NLO devices. [ABSTRACT FROM AUTHOR]

Zero-dimensional heterometallic halide hybrids have emerged as multifunctional emitters, due to their multiple emission features. Herein, high pressure is employed to regulate the multiple emissions of (C9NH20)9[Pb3Br11](MnBr4)2. Pressure-triggered rigidness of [Pb3Br11]5- alters the emission equilibrium of STEs, generating a new blue-shifted STE emission. Meanwhile, [MnBr4]2- contraction promotes the confinement effect to increase the 4D-6A1 transition efficiency. Notably, [Pb3Br11]5- could act as ‘antenna' to enhance the Mn2+ emission with blocked back-energy transfer. It indicates that enough incident energy could excite the STE emission and 4D-6A1 transitions simultaneously, which clarifies the conventional understanding of the emission origin at ambient conditions.

Piezochromic materials refer to a class of matters that alter their photoluminescence (PL) colors in response to the external stimuli, which exhibit promising smart applications in anti‐counterfeiting, optoelectronic memory and pressure‐sensing. However, so far, most reported piezochromic materials have been confined to organic materials or hybrid materials containing organic moieties with limited piezochromic range of less than 100 nm in visible region. Here, we achieved an intriguing piezochromism in all‐inorganic zero‐dimensional (0D) Cs3Cu2Cl5 nanocrystals (NCs) with a considerable piezochromic range of 232 nm because of their unique inorganic rigid structure. The PL energy shifted from the lowest‐energy red fluorescence (1.85 eV) to the highest‐energy blue fluorescence (2.83 eV), covering almost the entire visible wavelength range. Pressure‐modulated self‐trapped exciton emission between different energy levels of self‐trapped states within Cs3Cu2Cl5 NCs was the main reason for this piezochromism property. Note that the quenched emission, which is over five times more intense than that in the initial state, is retained under ambient conditions upon decompression. This work provides a promising pressure indicating material, particularly used in pressure stability monitoring for equipment working at extreme environments. [ABSTRACT FROM AUTHOR]

Zero-dimensional heterometallic halide hybrids have emerged as multifunctional emitters, due to their multiple emission features. Herein, high pressure is employed to regulate the multiple emissions of (C9NH20)9[Pb3Br11](MnBr4)2. Pressure-triggered rigidness of [Pb3Br11]5- alters the emission equilibrium of STEs, generating a new blue-shifted STE emission. Meanwhile, [MnBr4]2- contraction promotes the confinement effect to increase the 4D-6A1 transition efficiency. Notably, [Pb3Br11]5- could act as 'antenna' to enhance the Mn2+ emission with blocked back-energy transfer. It indicates that enough incident energy could excite the STE emission and 4D-6A1 transitions simultaneously, which clarifies the conventional understanding of the emission origin at ambient conditions. In zero-dimensional metal halide of (C9NH20)9[Pb3Br11](MnBr4)2, the [Pb3Br11]5- trimer acts as 'antenna' to enhance the [MnBr4]2- emission at high pressure, resolving distinct photoluminescent contributions of individual metal-halogen fragments. [ABSTRACT FROM AUTHOR]

Sb3+ doping strategy has proved to be an effective way to regulate the band gap and improve the photophysical properties of metal halides. Herein, Sb3+‐doped lead‐free indium halide hybrid InCl6(C4H12N2)2Cl·H2O:xSb3+ (0 ≤ x ≤ 1) is reported. Upon Sb3+‐doping, the weak emission of InCl6(C4H12N2)2Cl experiences a significant enhancement in emission intensity with near‐unity photoluminescence quantum yield (PLQY). The photophysical data fitted by the power‐law equation verifies self‐trapped exciton emission for the broadband emission. Interestingly, the emission experiences a gradual red‐shift with emission color changing from green to yellow and finally to orange as the Sb3+‐doped concentration increases. The single crystal X‐ray diffraction, excitation wavelengths‐dependent emission spectra, and the distortion degree calculation of InCl6(C4H12N2)2Cl·H2O:xSb3+ (0 ≤ x ≤ 1) indicate that the Sb3+ concentration dependent luminescence results from the synergistic effect of crystal phase transition, change of luminescence center, and the distortion of crystal structure. This achievement represents a successful strategy to achieve the photophysical properties modulation of metal halides for versatile optical applications. [ABSTRACT FROM AUTHOR]

Pressure-modulated self-trapped exciton (STE) emission mechanism in all-inorganic lead-free metal halide double perovskites characterized by large Stokes-shifted broadband emission, has attracted much attention across various fields such as optics, optoelectronics, and biomedical sciences. Here, by employing the all-inorganic lead-free metal halide double perovskite Cs 2 TeCl 6 as a paradigm, the authors elucidate that the performance of STE emission can be modulated by pressure, attributable to the pressure-induced evolution of the electronic state (ES). Two ES transitions happen at pressures of 1.6 and 5.8 GPa, sequentially. The electronic behaviors of Cs 2 TeCl 6 can be jointly modulated by both pressure and ES transitions. When the pressure reaches 1.6 GPa, the Huang-Rhys factor S, indicative of the strength of electron-phonon coupling, attains an optimum value of ≈12.0, correlating with the pressure-induced photoluminescence (PL) intensity of Cs 2 TeCl 6 is 4.8-fold that of its PL intensity under ambient pressure. Through analyzing the pressure-dependent STE dynamic behavioral changes, the authors have revealed the microphysical mechanism underlying the pressure-modulated enhancement and quenching of STE emission in Cs 2 TeCl 6 ., (© 2024 Wiley‐VCH GmbH.)

Chiral materials with circularly polarized luminescence (CPL) are currently attracting great attention for their wide applications in bioresponsive imaging, 3D displays, and storage of information. Herein, CPL‐active enantiomorphic hybrids (R)‐ and (S)‐C6H15Cl2NO⋅SbCl5 are obtained by self‐assembling chiral R/S‐(3‐chloro‐2‐hydroxypropyl)trimethylammonium chloride with antimony(III) chloride, giving a 0D structure with SbCl5 pyramids isolated by (3‐chloro‐2‐hydroxypropyl)trimethylammonium chloride cations. The formed enantiomers exhibit brilliant orange emission peaked at 604 nm with photoluminescence quantum yield as high as 71.2%, originating from the self‐trapped exciton emission demonstrated by photophysical characterization. Due to the existence of chiral organic cations, the enantiomers exhibit strong chiral‐optical properties with mirror‐image circular dichroism signals in ground state and obvious CPL activity with the dissymmetry factor glum of 2.5 × 10−4 and −1.6 × 10−4 for R‐type and S‐type, respectively. It should be mentioned that these are the first reported 0D hybrids with CPL‐activity. This work paves an avenue for developing eco‐friendly CPL materials with highly ‐efficient luminescence. [ABSTRACT FROM AUTHOR]

• Delicate distortions of [Sb 2 Cl 10 ]4− dimers dramatically promote self-trapped exciton emission. • Varied emission equilibrium of triplet excitons induces intense natural white emission. • Underlying Mechanisms determining dimeric self-trapped emission are analyzed. • High pressure is proposed to optimize photoluminescence properties of metal-halogen dimers. Zero-dimensional (0D) hybrid metal halides (HMHs), featured with unique self-trapped exciton (STE) emissions, are emerging photoluminescence (PL) materials for photoelectronic applications. Compared with metal-halogen monomers, dimeric units in 0D HMHs possess more structural flexibility and less spatial confinement of excitons, creating new opportunities for PL engineering. Herein, high pressure is employed on 0D (C 3 H 12 N 2) 2 Sb 2 Cl 10 to controllably distort inter- and intra-octahedral structures within [Sb 2 Cl 10 ]4− dimers. Intense natural white emission is achieved with dramatically increased photoluminescence quantum yield from less than ≈1% to 74.2 %. The high-pressure emission of (C 3 H 12 N 2) 2 Sb 2 Cl 10 is proven to originate from the STE recombination from triplet states with varied emission equilibrium, as well as the promoted excitonic trapping with restrained nonradiative recombination. This work offers valuable insights into the structure effects on STE emission and the transition mechanisms of metal-halogen dimers, which are crucial for developing novel metal halides for illumination. [ABSTRACT FROM AUTHOR]

We report on the luminescence properties of hydrothermally synthesized BaLuF 5 :Pr3+(1%) nanoparticles having a cubic crystal structure. The properties were investigated at low temperatures using time-integrated and time-resolved luminescence spectroscopy under VUV photon excitation in the energy range of 5–45 eV. This spectral region covers both the Pr3+ 4f2→4f15d1 transitions and the intrinsic absorption of the host material. Due to the weak crystal field, only the intra-configurational Pr3+ 4f2→4f2 transitions were observed, resulting in photon cascade emissions. According to structural and morphological studies, the nanoparticles, with an average size of 21 ± 4 nm, were found to possess large amounts of defects, which are further confirmed through luminescence spectroscopy. The influence of non-radiative decay at the surface and energy transfer to the defects are responsible for the shortening of luminescence decay detected for the 1S 0 transitions of Pr3+ ions and intrinsic UV cross-luminescence of host materials. We have discussed the specific energy transfer processes that populate various luminescence centers and evaluated BaLuF 5 :Pr3+(1%) nanoparticles for potential optical applications. • "Investigated luminescence properties of hydrothermally synthesized BaLuF5+:Pr3+(1 %) nanoparticles under VUV excitation". • "Photon cascade emission observed due to the 4f21S 0 level being below the 4f15d1 states". • "Structural and morphological studies reveal a significant amount of defects in nanoparticles". • "Non-radiative decay at surfaces and energy transfer to defects shorten luminescence decay times". • "Potential optical applications in fast timing due to ultrafast cross-luminescence and 1S 0 transitions of Pr3+ ions". [ABSTRACT FROM AUTHOR]

Perovskite metal halides have attracted extensive attention because of their excellent photoelectric properties and structural adjustability. Herein, the authors report a facile method for the controlled synthesis of cesium‐bismuth halides by controlling the stoichiometry of Cs/Bi precursors at room temperature. The 0D Cs3BiCl6 and 1D Cs3Bi2Cl9 can be obtained at the Cs/Bi feed ratio of 3:1 and 3:2, respectively. Though both metal halides exhibit a very low photoluminescence quantum yield (PLQY) due to their intrinsic nature of indirect band gaps, they exhibited bright orange broadband emission after Mn2+ doping. Combining density functional theory (DFT) calculations, it is found that an appropriate amount of Mn2+ doping does not change the crystal structures of cesium‐bismuth halides, but Mn 3d orbitals produce impurity states in the forbidden energy gaps of the host structures, resulting in efficient energy transfer from the conduction band of the host to d‐state of Mn ions. Importantly, the reversible structural switch of Mn‐doped Cs3BiCl6 and Cs3Bi2Cl9 metal halides can be flexibly adjusted through the post addition of the CsCl/BiCl3 precursors. These results tremendously enrich the synthetic chemistry of low‐dimensional metal halides and provide a beneficial reference for the regulation of crystal structure and optical properties of metal halides. [ABSTRACT FROM AUTHOR]

Self‐trapped exciton (STE) emission of low‐dimensional metal halides has witnessed explosive developments in both display and illumination, due to its intriguing photoluminescence properties. As one typical feature, STE emission energy is commonly independent of excitation wavelength. Herein, a rare phenomenon of inverse excitation‐dependent dual‐band emission is achieved on 0D Cs2InBr5·H2O. Under initial compression, the contraction of inhomogeneously coordinated InBr5O octahedra gives rise to blue‐shifted STE emission with the decreased Stokes shift. As the phase transition occurs under higher pressure, considerable octahedral distortions generate a new defect‐related localized exciton emission. Notably, the high‐energy emission from the intrinsic STE state is only observed under the low‐energy excitation, which is believed to originate from the excitation‐dependent multiple excited states in high‐pressure Cs2InBr5·H2O. [ABSTRACT FROM AUTHOR]

The pursuit of environmentally friendly and highly luminescent phosphors for down-conversion white light-emitting diodes (WLEDs) remains a significant focus of research. Here, we present a novel zero-dimensional Sn(II) hybrid exhibiting vibrant orange emission peaking at 598 nm and an outstanding photoluminescence quantum yield of 69%. This hybrid, designated as (C 7 H 8 N 3) 4 SnBr 6 , was synthesized via the reaction of 2-aminobenzimidazole with SnBr 2 , revealing distinctive self-trapped exciton emission characteristics, contributing to its broad-band emission and prolonged lifetime. Subsequently, a down-conversion WLED was constructed by integrating the Sn(II) hybrid with a green phosphor ((Sr, Ba) 2 SiO 4 :Eu2+) and a blue phosphor (BaMgAl 10 O 17 :Eu2+), resulting in CIE coordinates of (0.313, 0.331), a correlated color temperature of 6466 K, and an impressive color rendering index of 90.6. This work enriches the family of lead-free hybrid phosphors, showcasing their potential for highly efficient white LED applications. • A full-spectra WLED with a high CRI was fabricated by mixing the orange-yellow emissive 0D Sn(Ⅱ) hybrids with commercial blue and green phosphors. • The fabricated WLED shows good operating stability under constant current density. [ABSTRACT FROM AUTHOR]

Lead-free perovskite is a non-toxic and environmentally friendly material, which plays an increasingly significant role in photodetection, luminescence, photovoltaics and so on. In this paper, a single-component white light emission is successfully achieved through the co-doping of Sb3+, Mn2+ and Tb3+ in Cs 2 NaInCl 6. The photoluminescent mechanism is proved through the spectra measurements and decay dynamics. The addition of Sb3+ could activate the self-trapped exciton (STE) emission of the matrix (blue light at 450 nm). The efficient energy transfer from STE emission could realize red light emission of Mn2+, and green light emission of Tb3+. The single-component white light emission is obtained with the Commission Internationale de L'Eclairage of (0.31, 0.35), high color rendering index of 88.1 and correlated color temperature of 6394 K. Finally, the prepared white light emitting diodes demonstrate high performance and excellent stability. This provides a new idea for development of lead-free perovskite white luminescent materials in display and lighting applications. • The blue self-trapping exciton emission of Cs 2 NaInCl 6 is significantly enhanced through the sensitivity of Sb3+ ions. • The efficient energy transfer channels from matrix to Mn2+ and Tb3+ ions promote the formation of white light emission. • The prepared white light-emitting diodes display high performance and excellent stability. [ABSTRACT FROM AUTHOR]

The ϕ7 mm undoped Cs2 HfCl6 and Cs2 HfCl6 ∶0.2% Tl(mole fraction) single crystals were grown by the Vertical Bridgman method. The phase, impurities concentrations, luminescence and scintillation properties of crystal samples were studied. Both crystalsbelong to the cubic crystal structure and the space group of Fm3m. When excited by ultraviolet light and X-ray, both crystals exhibit an emission peak at 380 nm originated from self-trapped excitons emission, and Cs2 HfCl6 ∶0.2%Tl crystal exhibits an extra Tl+ sp-s² transition induced emission at 505 nm. Cs2 HfCl6 and Cs2 HfCl6 ∶0.2%Tl possess high light yields of 37 000 photons/MeV and 36 500 photons/MeV respectively and both have excellent energy resolutions of 3.5% at 662 keV under excitation of 137Cs source. The scintillation decay time of undoped Cs2 HfCl6 is comprised of 0.37 μs (4.2%), 4.27 μs (78.9%) and 12.52 μs (16.9%). The scintillation decay time of Cs2 HfCl6 ∶0.2% Tl is comprised of 0.33 μs (3.5%), 4.09 μs (81.9%) and 10.42 μs (14.5%). [ABSTRACT FROM AUTHOR]

Emerging lead‐free metal halides with low toxicity and unparalleled optoelectronic properties have attracted growing research interests, also demonstrating extensive application potentials. Among these, Sb3+‐based all‐inorganic/organic–inorganic hybrid metal halides become a vital group due to the special energy level distribution along with diverse optical properties. However, there remains a gap in understanding the relationship between the crystal structure and the radiation process of involved Sb3+ emission. Herein, the existing reports about Sb3+‐based luminescent metal halides are revisited and their structure–luminescence–application relationship is explored, and it is further established that the triplet self‐trapped excitons (STEs) emission of Sb3+ varies in different crystallographic environments and endows tunable luminescent performance. This work aims to provide constructive strategies in the further exploitation of Sb3+‐based metal halides, and also guides the structural design and photoluminescence tuning of doped metal halide materials. [ABSTRACT FROM AUTHOR]

Zero‐dimensional (0D) hybrid metal halides are promising light emitters. However, it is still challenging to accurately design their structures with targeted photoluminescence properties. Herein, high pressure is used to change the self‐trapped exciton (STE) emission of 0D (bmpy)9[ZnBr4]2[Pb3Br11] (bmpy: 1‐butyl‐1‐methylpyrrolidinium). Under initial compression, the simultaneous contraction and distortion of photoactive [Pb3Br11]5− vary the equilibrium of STE emissions between different excited states, tuning the emission color from yellow green to cyan. Notably, sufficient structural distortion under continuous compression leads to the formation of more and deeper STE states, exhibiting an unprecedented broadband white‐light emission. This study reveals the structure‐dependent optical properties of 0D hybrid metal halides, providing novel insights into the mechanism of STE emission. [ABSTRACT FROM AUTHOR]

Zero-dimensional organic-inorganic metal halide hybrids provide ideal bulk-crystal platforms for exploring the pressure engineering of electron-phonon coupling (EPC) and self-trapped exciton (STE) emission at the molecular level. However, the low stiffness of inorganic clusters hinders the reversible tuning of these physical properties. Herein, we designed a Sb 3+ -doped metal halide with a high emission yield (89.4%) and high bulk modulus (35 GPa) that enables reversible and enhanced STE emission (20-fold) under pressure. The high lattice rigidity originates from the corner-shared cage-structured inorganic tetramers and ring-shaped organic ligands. Further, we reveal that the pressure-enhanced emission regime below 4.5 GPa is owing to the lattice hardening and preferably EPC strength reducing, while the pressure-insensitive emission regime within 4.5-8.5 GPa results from the enhanced intercluster Coulombic attraction force that resists intracluster compression. These results provide insights into the structure-property relation and molecular engineering of zero-dimensional metal halides toward wide-band and pressure-sensitive light sources.

Pr3+-activated yttrium-based compounds have garnered significant research interest as the electronic transition of Pr3+ dopant incorporated in host lattices are quite versatile, giving rise to the production of either UV or visible electromagnetic radiation. The tunable 5d orbital energy level of Pr3+ with an electronic configuration [Xe]4f15d1 depending on the external crystal fields, coordinating anion ligands (mainly determined by covalency of anion ligands), and symmetry of crystal structures can indeed control the radiative decay processes whether to generate UV or self-trapped exciton-mediated visible emission. We have investigated three different Pr3+-activated crystals of YPO 4 , YBO 3 , and Y 2 SiO 5 using two different excitation processes including direct host lattice excitation (cathodoluminescence: CL) and f-d excitation of Pr3+ dopants (photoluminescence: PL). Such radiative decay mechanism observed in Pr3+-doped yttrium-based compounds has been deciphered that photoexcitation of Pr3+ ions results in 4f15d1→4f2 electronic transition with UV emission (PL) whereas above-bandgap excitation of host lattices brings about the efficient production of visible emission mediated through self-trapped excitons (CL). When changing the anion sublattices, the emission peak corresponding to 4f15d1→4f2 transition shifted to longer wavelength as a result of modulated covalency and crystal field strength. As the host lattices changes as a function of anion sublattices, the bandgap reduced from 8.6 eV (for YPO 4) to 7.6 eV (for YBO 3) and to 6.1 eV (for Y 2 SiO 5), directly influencing rate of trapping of exciton and their formation of self-trapped exciton, which further give rise to production of the self-trapped exciton mediated visible emission. The fundamental understanding of the multiple, radiative relaxation pathways provides a designing principle for achieving more efficient UV emitting phosphors (at the same time by suppressing visible emission or vice versa) for germicidal and medical applications. [Display omitted] • Mechanistic understanding of radiative relaxation of Pr3+, resulting in either UV and visible emission, is importantfor designing phosphors. • Relative ratio of UV/visible emission were investigated as a function of varying a type of coordinating anion sublattice, covalency, and bandgap. • Direct host lattice excitation (with electron beam bombardment) or excitation of f-d state of Pr3+ (photoexcitation) determines different radiative relaxation pathways. [ABSTRACT FROM AUTHOR]

Phase-pure crystalline micropowder samples of BaGeF 6 were prepared and studied under excitation by tuneable synchrotron radiation and 10 keV electron beam. Time-resolved photoluminescence emission and excitation spectra and a set of single emission decay curves were recorded at 7 K for the exciting photon energy region of 4.3–45 eV. Several intrinsic emissions were revealed in BaGeF 6 and their origin investigated. A single broad emission band peaking at 455 nm is assigned to be of excitonic origin due to its long decay time in the μs range and due to the presence of an intense excitation peak at 10.1 eV right in the region of the host absorption onset. The energy gap width of BaGeF 6 was determined experimentally from the photoluminescence excitation spectra of the 455 nm emission to be 10.9 eV. Several emission bands, including distinct peaks at 270 and 455 nm, with the main decay component of ∼180 ps were revealed across the wavelength range of 200–500 nm. The revealed ultrafast emissions were studied by means of time-resolved photoluminescence spectroscopy and their origin was assigned to cross-luminescence resulting from radiative transitions between the Ba 5p core level and sub-bands of the valence band (Ge 4s, Ge 4p and F 2p hybridized states) and to intraband luminescence between the valence band sub-bands. Photoluminescence excitation spectra of the ultrafast emissions revealed a gently sloping onset at 17 eV, related to transitions from the Ge 4s states. It is followed by a distinct peak at 19.4 eV, which corresponds to the ionization of the Ba 5p cation states and is related to the excitation threshold of cross-luminescence. • Crystalline BaGeF 6 microrods were synthesized and characterized using XRD and SEM. • Ultrafast emissions (∼180 ps) were revealed in the UV-to-visible spectral range. • Cross-luminescence is due to transitions from Ba 5p to Ge 4s, 4p and F 2p states. • Intraband luminescence is due to transitions between Ge 4s,4p, F 2p valence bands. • Electronic band structure parameters of BaGeF 6 were experimentally determined. [ABSTRACT FROM AUTHOR]

0D hybrid metal halides (0D HMHs) are considered to be promising luminescent emitters. 0D HMHs commonly exhibit self-trapped exciton (STE) emissions originating from the inorganic metal halide anion units. Exploring and utilizing the emission features of the organic cation units in 0D HMHs is highly desired to enrich their optical properties as multifunctional luminescent materials. Here, tunable emissions from organic and inorganic units are successfully achieved in triphenylsulfonium (Ph 3 S + )-based 0D HMHs. Notably, integrated afterglow and STE emissions with adjustable intensities are obtained in (Ph 3 S) 2 Sn 1- x Te x Cl 6 (x = 0-1) via the delicate combination of [SnCl 6 ] 2- and [TeCl 6 ] 2- . Moreover, such a strategy can be readily extended to develop other HMH materials with intriguing optical properties. As a demonstration, 0D (Ph 3 S) 2 Zn 1- x Mn x Cl 4 (x = 0-1) are constructed to achieve integrated afterglow and Mn 2+ d-d emissions with high efficiency. Consequently, these novel 0D HMHs with colorful afterglow and STE emissions are applied in multiple anti-counterfeiting applications., (© 2022 Wiley-VCH GmbH.)

• Crystalline K 2 GeF 6 particles were synthesized by co-precipitation. • Fast cross- and intraband luminescence with decay times 300–500 ps was observed. • Transitions between valence sub-bands (Ge 4s,4p, F 2p) cause intraband luminescence. • The decay of K 3p cation excitons results in the formation of Ge 4s,4p holes. • Electronic band structure parameters of K 2 GeF 6 were experimentally determined. Highly crystalline K 2 GeF 6 micropowders were prepared by co-precipitation in the hydrofluoric acid-water-alcohol solution and studied by means of the cathodoluminescence and time-resolved luminescence spectroscopy under synchrotron radiation excitation at 7 K. The nature of various intrinsic emissions was revealed. The luminescence band at 510 nm detected under excitation by photons with the energy above 9 eV is related to the radiative decay of self-trapped excitons. Fast emission bands with ~400 ps decay time found in the spectral range from VUV to visible (8–2.4 eV) are assigned to the cross-luminescence transitions from K 3p hole states and intraband luminescence transitions due to the presence of the Ge 4s, 4p valence states. The creation of cation excitons was detected in the energy range 18–20 eV. Their non-radiative decay results in the formation of hole states in the Ge energy bands, which finally recombine with electrons from the above lying valence states and provide fast intraband luminescence. Important electronic band structure parameters including the energy gap width of 11 eV, cation exciton formation energy 18.1 eV and ionization energy of cation states 20.0 eV were determined from the luminescence excitation spectra. [ABSTRACT FROM AUTHOR]