Recently, low-dimensional organic−inorganic lead halide perovskites have attracted a great deal of attention due to their outstanding tunable broadband emission, while the toxicity of lead hinders their further application in the photoelectric field.Here, we report a novel lead-free Cu(I)-based organic−inorganic perovskite-related material of a (MA) 4 Cu 2 Br 6 single crystal with zero-dimensional clusters, which is a unique Cu 2 Br 6 4− cornersharing tetrahedron dimer structure consisting of two connected tetrahedra. The single crystal displays a bright broadband green emission with a high photoluminescence with a quantum yield of ≤93%, a large Stokes shift, and a very long (microsecond) photoluminescence (PL) lifetime, resulting from self-trapped exciton emission. The direct band gap characteristic of (MA) 4 Cu 2 Br 6 was proven by density functional theory calculation, and its band gap was determined by experiments to be ∼3.87 eV. In the temperature range of 98−258 K, the PL intensity increases gradually with an increase in temperature due to the deep trapping out of strong electro-phonon coupling, while the PL decreases when the temperature increases over 258 K due to phonon scattering. It is worth mentioning that this new material has high chemical and light stability, in contrast to the lead perovskite.

Zero-dimensional lead-free organic–inorganic hybrid metal halides have drawn attention as a result of their local metal ion confinement structure and photoelectric properties. Herein, a lead-free compound of (Gua)3Cu2I5 (Gua = guanidine) with a different metal ion confinement has been discovered, which possesses a unique [Cu2I5]3– face-sharing tetrahedral dimer structure. First-principles calculation demonstrates the inherent nature of a direct band gap for (Gua)3Cu2I5, and its band gap of ∼2.98 eV was determined by experiments. Worthy of note is that (Gua)3Cu2I5 exhibits a highly efficient cool-white emission peaking at 481 nm, a full-width at half-maximum of 125 nm, a large Stokes shift, and a photoluminescence quantum efficiency of 96%, originating from self-trapped exciton emission. More importantly, (Gua)3Cu2I5 single crystals have a reversible thermoinduced luminescence characteristic due to a structural transition scaled by the electron–phonon coupling coefficients, which can be converted back and forth between cool-white and yellow color emission by heating or cooling treatment within a short time. In brief, as-synthesized (Gua)3Cu2I5 shows great potential for application both in single-component white solid-state lighting and sensitive temperature scaling.

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Zero-dimensional (0D) metal halides are in a blossoming status for their fascinating optoelectronic properties. Herein, an antimony-based metal halide of (C 16 H 28 N) 2 -SbCl 5 (C 16 H 28 N + = benzyltripropylammonium cations), where the isolated [SbCl 5 ] 2− clusters are surrounded by C 16 H 28 N + to form a 0D square-pyramidal structure, was synthesized and investigated. The (C 16 H 28 N) 2 SbCl 5 exhibited a broadband orange emission at 633 nm upon the low-energy irradiation (400 nm) with a near-unity photoluminescence quantum efficiency (97.8%). Interestingly, (C 16 H 28 N) 2 SbCl 5 showed an additional emission peak at 477 nm upon the higher-energy irradiation (300 nm), which is attributed to the transformation of the doublet of spin-orbit couplings into two independent self-trapped excitons (STEs). Temperaturedependent Raman spectra clearly revealed the characteristics of multi-phonon coupling, demonstrating a strong anharmonic electron-phonon interaction in (C 16 H 28 N) 2 SbCl 5 . Temperature-dependent emission spectra and density functional theory results illustrated that the observed dual-band emission originated from singlet and triplet STEs in [SbCl 5 ] 2− units. Combined with the efficient emission and excellent stability of (C 16 H 28 N) 2 SbCl 5 , a stable white-light-emitting diode with an ultra-high color rendering index of 96.6 was fabricated.

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Here, we report (C 4 H 9 ) 4 NCuCl 2 single crystals with a luminous intensity that remains largely the same after soaking in water for 24 h. (CH 9 ) 4 NCuCl 2 has a new type zerodimensional framework, in which the isolated [CuCl 2 ] − anions are wrapped by organic (C 4 H 9 ) 4 N + cations. As expected, (C 4 H 9 ) 4 NCuCl 2 shows a broad emission band at 508 nm with a photoluminescence quantum yield of approximately 82% at room temperature, stemming from self-trapped exciton (STE) emission. Temperature-dependent photoluminescence measurement reveals that there is an energy barrier ΔE (24.0 meV) between the intrinsic state and STE state, which leads to the increase in emission intensity with an increase in temperature (98−278 K), while the emission intensity begins to decrease when the temperature is higher than 278 K due to the effects of both thermal quenching and carrier scattering. Our findings provide a new idea for the design of lead-free anti-water stability metal halide materials.

Recently, cuprous halide perovskite-type materials have drawn tremendous attention for their intriguing optical properties. Here, a zero-dimensional (0D) Cu­(I)-based compound of [(C3H7)4N]2Cu2I4 ([C3H7)4N]+ = tetrapropylammonium cation) was synthesized by a facile solution method, a monoclinic system of P21/n symmetry with a Cu2I4 2– cluster as the confined structure. The as-synthesized [(C3H7)4N]2Cu2I4 exhibits bright dual-band pure white emission with a photoluminescence quantum yield (PLQY) of 91.9% and CIE color coordinates of (0.33, 0.35). Notably, this compound also exhibits an ultrahigh color rendering index (CRI) of 92.2, which is comparable to the highest value of single-component metal halides reported recently. Its Raman spectra provide a clear spectral profile of strong electron–phonon interaction after [(C3H7)4N]+ incorporation, favoring the self-trapped exciton (STE) formation. [(C3H7)4N]2Cu2I4 can give dual-STE bands at the same time because of the Cu–Cu metal bond in a Cu2I4 2– cluster, whose populations could be scaled by temperature, together with the local dipole orientation modulation of neighboring STEs and phase transition related emission color coordinate change. Particularly, the outstanding chemical- and antiwater stability of this compound was also demonstrated. This work illustrates the potential of such cuprous halide perovskite-type materials in multifunctional applications, such as lighting in varied environments.