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The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in, e.g. phosphor‐converted white light‐emitting diodes (pc‐wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5–3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal‐ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer‐like borosulfate ligand in the Mn2+‐containing solid solutions Zn1‐xMnx[B2(SO4)4] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2(SO4)4]:Mn2+ shows orange narrow‐band luminescence at 590 nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn−O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal‐ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors. [ABSTRACT FROM AUTHOR]

The anionic diamido N‐heterocyclic carbene 1 is used to prepare a series of linear as well as trigonal, heteroleptic CuI complexes with small molecular ligands such as pyridine derivatives or triphenylphosphine. A key role lies in the versatile precursor for these complexes, a moisture‐ and air‐stable 1D coordination polymer [1 ⋅ Cu]n composed of only the NHC ligand and CuI, such that the copper is linearly coordinated by the carbene carbon atom and one oxygen atom of the backbone of the carbene. This polymer can easily be cleaved into monomeric complexes by addition of the desired ligand to dispersions of the polymer in dichloromethane. In solution, the complexes are in equilibrium with this highly insoluble polymer and free ligand. Thus, analytical and spectroscopical experiments with the compounds are limited to their crystalline state, characterized by single crystal X‐ray diffraction experiments. Some of the complexes exhibit visible luminescence in the solid state upon irradiation with ultraviolet light. The spectral features (emission wavelength, Stokes shift, width of the emission band, vibrational fine structure) significantly differ among the complexes. Quantum mechanical computations reveal a subtle interplay of several factors such as coordination number and charge transfer character of the emissive state. [ABSTRACT FROM AUTHOR]

Inorganic hosts, such as SrB4O7 or certain nitrides, intrinsically stabilize Eu2+ even when the dopant is an Eu3+‐based precursor and reducing conditions are not employed in the synthesis. Although this concept is well known in the synthesis of phosphorescent materials, the mechanistic details are scarcely understood. Herein, we demonstrate that trapped charge carriers, such as color centers, can also act as redox partners to stabilize certain oxidation states of activators. Eu‐activated CsMgCl3 and CsMgBr3 are used as examples. Upon doping with EuCl3 and in the absence of reducing conditions during the synthesis, dominant cyan or green luminescence from Eu2+ ions was observed. Photoluminescence spectroscopy at 10 K revealed that the reduction is correlated to color centers localized at defects. Although defects are typically undesired in phosphors, we have shown that their role may be underestimated and they could be used on purpose in the preparation of selected inorganic phosphors. [ABSTRACT FROM AUTHOR]

Borosulfates are weakly coordinating ligands, which is directly reflected in the photoluminescence properties of the Mn SP 2+ sp ions: They show orange narrow emission, which is indicative for a weak octahedral ligand field, as explained by Jörn Bruns, Markus Suta et al. in their Research Article (e202309212). Borosulfates are weakly coordinating ligands, which is directly reflected in the photoluminescence properties of the Mn SP 2+ sp ions: They show orange narrow emission, which is indicative for a weak octahedral ligand field, as explained by Jörn Bruns, Markus Suta et al. in their Research Article (e202309212). Keywords: Borosulfate; Mn2+; Photolumineszenz; Schwach Koordinierend DE Borosulfate Mn2+ Photolumineszenz Schwach Koordinierend 1 1 1 10/31/23 20231106 NES 231106 B Mn b SP B 2+ b sp B b is a so-far still rather underestimated visible emitter that is more abundant than the currently dominantly used emitter Eu SP 2+ sp . [Extracted from the article]

Abstract In this review, modern insights into the synthesis and fundamental optical properties as well as applications of divalent lanthanides as spectral energy converters are discussed, which have especially evolved within the last two decades. An emphasis is put on the state-of-the-art knowledge about the luminescence of other divalent lanthanides than the most commonly applied representative Eu2+ and what special features in their luminescence arises due to the different number of 4f n electrons. In particular, the luminescence of Sm2+, Tm2+, Yb2+ and the less stable ions Nd2+ and Dy2+ will be regarded. A broad overview over the synthetic approaches to inorganic compounds based on divalent lanthanide ions will be conveyed as well and shall demonstrate the fascinating developments in the field of inorganic solid-state chemistry of the lanthanides. Besides their fundamental optical properties, also applications of the presented divalent lanthanide activators are discussed. Sm2+ is a well-known temperature and pressure sensor due to its interconvertible 4f‐4f and 5d-4f transitions. Moreover, nanocrystalline BaFCl:Sm2+ has an appreciable potential as novel X-ray storage phosphor. Tm2+ is interesting for upconversion in photovoltaic and lasing applications, whereas Yb2+ in halides may be a promising alternative to Eu2+ for scintillation materials and phosphors for light-emitting diodes (LEDs). Nd2+ and Dy2+ are currently emerging as novel near infrared (NIR)-absorbing and emitting activators that might become interesting as lasing ions. The spectroscopy of these unusual lanthanide ions provides many non-trivial features due to the excited two-open shell 4fn-15d1 configuration overlapping with the excited 4f n levels. Finally, a perspective for future developments will be given. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and photoluminescence properties of the bright‐yellow organocerium complex [{(Cp t Bu 2 )2Ce(μ‐Cl)}2] (Cp t Bu 2 =1,3‐di(tert‐butyl)cyclopentadienyl) are presented. This coordination compound exhibits highly efficient photoluminescence within the yellow‐light wavelength range, with a high internal quantum yield of 61(±2) % at room temperature. The large red shift is attributed to the delocalizing ability of the aromatic ligands, whilst its quantum yield even makes this compound competitive with Ce3+‐activated LED phosphors in terms of its photoluminescence efficiency (disregarding its thermal stability). A bridging connection between two crystallographically independent Ce3+ ions is anticipated to be the reason for the highly efficient photoluminescence, even up to room temperature. The emission spectrum is characterized by two bands in the orange‐light range at both 10 K and room temperature, which are attributed to the parity‐allowed transitions 5d1(2D3/2)→4f1(2F7/2) and 5d1(2D3/2)→4f1(2F5/2) of Ce3+, respectively. The photoluminescence spectra were interpreted in relation to the structure and vibrational modes of the coordination compound. The spectra and optical properties indicate that trivalent cerium ions are the dominant species in the ground state, which also resolves an often‐encountered ambiguity in organocerium compounds. This result shows that photoluminescence spectroscopy is a versatile tool that can help elucidate the oxidation state of Ce in such compounds. [ABSTRACT FROM AUTHOR]

The photoluminescence properties of the homoleptic lanthanide(II) coordination compounds [Eu(Tp iPr2 ) 2 ] and [Yb(Tp iPr2 ) 2 ] (Tp iPr2 =hydro-tris(3,5-diisopropylpyrazolyl)borate) at 10 K and room temperature are presented and their relationship to the structure is discussed in detail. Both compounds are characterized by broad-banded luminescence which is typical for the 5 d ↔4 f transitions of divalent lanthanide ions. [Eu(Tp iPr2 ) 2 ] shows a remarkably bright greenish emission located at around 550 nm (18,180 cm -1 ) with a very small effective full width at half maximum (FWHM) (54 nm or 1860 cm -1 at 10 K; 70 nm or 1910 cm -1 at 300 K) and a correspondingly small Stokes shift (2150 cm -1 at 10 K; 2830 cm -1 at 300 K). These results are related to the huge rigidity of the complex within the crystal structure. The decay time 0f 0.86 µs is also typical for Eu 2+ -based coordination compounds. [Yb(Tp iPr2 ) 2 ] shows red emission with an asymmetric band peaking at around 642 nm (15,580 cm -1 ) and a similarly small Stokes shift (1540 cm -1 at 10 K; 2260 cm -1 at 300 K) and effective FWHM (50 nm or 1240 cm -1 at 10 K; 162 nm or 3010 cm -1 at 300 K). The long decay time of 0.12 ms at 10 K indicates the sole presence of a spin-forbidden emission, which is explained by interactions of the excited electronic states with highly energetic vibrations of the Tp iPr2 ligands. This enhances non-radiative relaxation from the excited low spin to the lowest excited high spin state of Yb 2+ . Moreover, the effect of the vibronic coupling on the luminescence quenching in [Yb(Tp iPr2 ) 2 ] is discussed. The optical properties nicely illustrate that the presented scorpionate complexes are an intermediate case between metallocenes and lanthanide-activated nitrides that are also in current use for LED applications. [ABSTRACT FROM AUTHOR]

In this paper, the temperature dependence of the photoluminescence of Yb2+ doped into the halidoperovskites CsMX3 (M = Ca, Sr; X = Cl, Br, I) is presented. Yb2+ shows spin-forbidden high-spin (HS) and spin-allowed low-spin (LS) emission bands in all compounds. Upon excitation of the higher energetic LS transition, very different behaviors of the interplay of the two emissive transitions are observed. In the chlorides, the HS-based emission becomes already dominant at higher temperatures than 50 K; in the bromides, a temperature-dependent population of the HS state is observed at higher temperatures than 200 K, whereas in the iodides, the LS emission remains dominant even above 300 K. A vibrational relaxation model is attempted for the explanation of this behavior that reveals a very delicate dependence on the mode energies of the [YbX6]4− octahedra. FIR spectra of the pure Yb2+-based compounds CsYbX3 are also presented to experimentally verify the estimated average mode energies from the model. Finally, the relevance for novel Yb2+-based scintillators is discussed. [ABSTRACT FROM AUTHOR]

The new microporous metal organic framework [La2(H2O)5(H2TPPE)]·3H2O (CAU‐54), is obtained in a hydrothermal reaction of the linker 1,1,2,2‐tetrakis(4′‐phosphonophenyl)ethylene (H8TPPE) and La3+ ions. The extensive characterization including temperature‐dependent crystal structures and spectroscopic properties allowed to understand the unique, multi‐responsive material properties. CAU‐54 exhibits rarely observed reversible photochromism as well as turn‐on photoluminescence by various external chemical or physical stimuli including change of pressure, solvent exchange, and temperature variation. These properties can be unequivocally assigned to the presence of tetraphenylethylene (TPE) moieties of the linker molecules within the MOF, i.e., the ordered spatial arrangement of the linker molecules, the presence of accessible pores as well as the coordination flexibility of the phosphonate groups and the rotational freedom of the linker. By temperature‐dependent steady‐state and time‐resolved luminescence studies, it is shown that this compound exhibits a) blue fluorescence that becomes effectively quenched at room temperature, b) green efficient luminescence with thermal stability up to 400 K, and c) red phosphorescence correlated to the observed photochromism. In addition, CAU‐54 shows unusual thermal expansion properties as shown by temperature‐dependent powder X‐ray diffraction measurements with identified transition points that correlate with the observed temperature‐dependent changes in the photoluminescence. [ABSTRACT FROM AUTHOR]

The Tb3+7F 5 level has been shown to play an important role in the energy transfer involving this ion. This is due to the unusually long lifetime of this level which is commonly disregarded when treating energy transfer involving this ion. In this work, we give a rationalized explanation for this phenomenon. It is discussed that the 7F 5 level can be fed by an energy transfer process and the population is trapped due to a low decay rate, which is related to the energy gap to the 7F 6 ground level in the far infrared and the correspondingly low photon density of states. This is in agreement with experimental data from direct measurements of the total decay lifetimes of the 7F 5 level and the emission quantum yields when this level is considered as an energy acceptor in Tb3+ compounds. [Display omitted] • The Tb3+7F 5 level population is rationalized, this is of high relevance in energy transfer processes involving this ion. • The 7F 5 level could have a high population fraction when compared with the 7F 6 ground level. • Multiphonon and radiative rates between 7F J levels were estimated. • A rate equation model was used to estimate the 7F 5 population fraction. [ABSTRACT FROM AUTHOR]