Analogous Chain Selenite Chlorides Ba2M(SeO3)2Cl2 (M = Cu2+, Ni2+, Co2+, Mn2+) and Pb2Cu(SeO3)2Cl2 with Tunable Spin S: Syntheses and Characterizations

A series of analogous chain selenite chlorides Ba2M(SeO3)2Cl2 (M = Cu 1, Ni 2, Co 3, Mn 4) and Pb2Cu(SeO3)2Cl2 5 with tunable spin S from S = 1/2 to S = 5/2 have been hydrothermally synthesized and characterized. These analogues crystallized in the orthorhombic Pnnm space group (monoclinic P21/n space group for 5) all containing M2+-SeO3-M2+ spin chains, which are further separated by the Ba2+ ions (Pb2+ for 5). The magnetic susceptibility results of 1, 2, and 5 show broad maxima around 80.0, 18.9, and 78.0 K, respectively, indicating good one-dimensional (1D) magnetism. Meanwhile, no long-range order (LRO) is observed down to 2 K for both 1 and 5, while the isostructural compounds 2, 3, and 4 exhibit LRO at 3.4 K, 10.8 K, and 5.7 K, respectively, which are further confirmed by the heat capacity and electron spin resonance results, as well as the observed spin-flop transitions in the M-H curves measured at 2 K below TN. The magnetizations of 1-5 at 7 T are still far from saturation. In addition, thermal stability and FT-IR and UV-vis-NIR spectroscopy of 1-5 are reported.

Realization of Broadband Near-Infrared Emission with High Thermal Stability in YGa3(BO3)4: Cr3+ Borate Phosphor

As a key material for phosphor-converted light-emitting diodes (pc-LEDs) applications, broadband near-infrared (NIR) phosphors currently face poor thermal stability issues. In this work, we synthesized a broadband near-infrared phosphor YGa3(BO3)4: Cr3+ (YGBO: Cr3+) with a high thermal stability. The YGBO: Cr3+ sample exhibits a broadband near-infrared emission centered at 770 nm with a full width at half-maximum (fwhm) of 2130 cm-1 under blue light excitation. Benefiting from the borate host crystal's strong structural rigidity, wide optical band gap, and weak electron-phonon coupling strength, YGBO: Cr3+ demonstrates strong luminescence thermal stability, and the corresponding luminescence intensity can maintain 80% at 150 °C compared to room temperature. Furthermore, we fabricated a pc-LED device using a blue light chip and YGBO: Cr3+ phosphor, and confirmed its application potential as a near-infrared light source in the spectral analysis of fruit freshness.

Deep red emission from rare-earth-free calcium aluminozincate phosphor with the substitution of Cr3+ ion

Chromium-doped calcium aluminozincate phosphor with a distinct amount of chromium was prepared via the sol-gel technique. The phase analysis and morphological study along with optical properties were conducted on the prepared material. The room temperature luminescent traits of the sample were studied in detail under 540 nm excitation wavelength. The deep red emission was confirmed from the CIE coordinates calculated using emission data. The decay curves were recorded to calculate the lifetime values for the aforementioned powder samples. The temperature-dependent luminescent characteristics were also investigated to identify the activation energy and thermal stability. The quantum yield was also calculated using luminescence spectra and found to be relatively good for the present phosphor. All of the investigated studies specified above signify that the synthesized phosphor is well suited as a red emitter in lighting and display devices.

Intense Luminescence and Good Thermal Stability in a Mn2+-Activated Mg-Based Phosphor with Self-Reduction

White light-emitting diodes provide widespread applications in lighting, electronic equipment, and high-tech displays. However, thermal quenching effect severely limits their practical application. Here, we developed an orange-red phosphor β-KMg(PO₃)₃:Mn²⁺, which emits bright orange-red light when excited by ultraviolet light without the energy transfer of sensitizer, owing to the strong crystal field provided by β-KMg(PO₃)₃ for Mn²⁺. The self-reduction of Mn⁴⁺ → Mn²⁺ and good thermal stability have been realized in an ambient atmosphere. The defect types were verified by X-ray photoelectron spectroscopy, and cationic vacancy plays a significant role in the self-reduction of Mn⁴⁺ → Mn²⁺. Furthermore, the properties of the trap energy levels were studied by thermoluminescence. The recombination luminescence of the detrapped carriers released from the deep trap levels at high temperatures suppresses the luminescence loss of thermal quenching. Moreover, the trap energy levels play an important role in the mechanoluminescence of β-KMg(PO₃)₃:Mn²⁺. This work emphasizes the significance of the defects in the luminescent characteristics and opens up a new approach for the development of advanced optical functional materials.

Photoluminescence Properties of AScSi2O6:Cr3+ (A = Na and Li) Phosphors with High Efficiency and Thermal Stability for Near-Infrared Phosphor-Converted Light-Emitting Diode Light Sources

Near-infrared (NIR) phosphors are fascinating photoluminescence materials with applications in phosphor-converted light-emitting diodes (pc-LEDs) for night vision lighting, which are still restricted by low efficiency and thermal stability in the current research stage. In this work, AScSi₂O₆ (A = Na/Li) are chosen as hosts due to a larger band gap and a single octahedral site for Cr³⁺ doping. The NIR-emitting Cr³⁺-activated AScSi₂O₆:Cr³⁺ phosphors were successfully prepared by a common high-temperature solid-state method. X-ray diffraction and Rietveld refinement confirm that the Cr³⁺ prefers to enter the Sc³⁺-octahedral lattice site in the AScSi₂O₆ structure. Under blue light excitation, AScSi₂O₆:Cr³⁺ phosphors exhibit broadband NIR emission from 700 to 1100 nm with a full width at half-maximum of ∼150 nm owing to the ⁴T₂ → ⁴A₂ electron transition of Cr³⁺. The photoluminescence properties were enhanced by adjusting the fluxes and sintering conditions, and highly efficient LiScSi₂O₆:Cr³⁺ NIR phosphors with external quantum efficiencies of 33.4% were obtained. Moreover, the optimized LiScSi₂O₆:Cr³⁺ exhibits excellent thermal stability (75% at 150 °C) with an activation energy of 0.33 eV. Importantly, the fabricated NIR pc-LED with the highly efficient LiScSi₂O₆:Cr³⁺ phosphor demonstrates brighter NIR light and a higher luminous efficacy than the NaScSi₂O₆:Cr³⁺ phosphor in night vision.

Cycloidal Magnetic Order Promoted by Labile Mixed Anionic Paths in M2(SeO3)F2 (M = Mn2+, Ni2+)

Two M₂(SeO₃)F₂ fluoro-selenites (M = Mn²⁺, Ni²⁺) have been synthesized using optimized hydrothermal reactions. Their 3D framework consists of 1D-[MO₂F₂]^4-chains of edge-sharing octahedra with a rare topology of alternating O-O and F-F μ₂ bridges. The interchain corner-sharing connections are assisted by the mixed O vs F anionic nature and develop a complex set of M-X-M superexchanges as calculated by LDA+U. Their interplay induces prominent in-chain antiferromagnetic frustration, while the interchain exchanges are responsible for the cycloidal magnetic structure observed below T_N ≈ 21.5 K in the Ni²⁺ case. For comparison the Mn²⁺ compound develops a nearly collinear spin (canted) ordering below T_N ≈ 26 K with ferromagnetic chain units.

(Ba,Sr)LaZnTaO6:Mn4+ far red emitting phosphors for plant growth LEDs: structure and photoluminescence properties

Application of (Ba,Sr)LaZnTaO₆:Mn⁴⁺ far red light emitting LEDs in plant lighting

M2(SeO3)F2 (M = Zn, Cd): understanding the structure directing effect of [SeO3]2− groups on constructing ordered oxyfluorides

The structure directing effect of [SeO₃]²⁻ anionic groups play a crucial role in the configuration of ordered [MO₃F₃] octahedral and its large anisotropy.

Transition Metal Selenite Halides: A Fascinating Family of Magnetic Compounds

The problem of searching for low-dimensional magnetic systems has been a topical subject and has attracted attention of the chemistry and physics community for the last decade. In low-dimensional magnetic systems, magnetic ions are distributed anisotopically and form different groups such as dimers, chains, ladders, or planes. In 3D frameworks, the distances between magnetic ions are equal in all directions while in low-dimensional systems the distances within groups are different from those between groups. The main approach of searching for desired systems is a priori crystal chemical design expecting the needed distribution of transition metal ions in the resulting structure. One of the main concepts of this structural design is the incorporation of the p-element ions with stereochemically active electron pairs and ions acting as spacers in the composition. Transition metal selenite halides, substances that combine SeO32− groups and halide ions in the structure, seem to be a promising object of investigation. Up to now, there are 33 compounds that are structurally described, magnetically characterized, and empirically tested on different levels. The presented review will summarize structural peculiarities and observed magnetic properties of the known transition metal selenite halides. In addition, the known compounds will be analyzed as possible low-dimensional magnetic systems.

Tailored Near-Infrared Photoemission in Fluoride Perovskites through Activator Aggregation and Super-Exchange between Divalent Manganese Ions

Biomedical imaging and labeling through luminescence microscopy requires materials that are active in the near-infrared spectral range, i.e., within the transparency window of biological tissue. For this purpose, tailoring of Mn²⁺-Mn²⁺ activator aggregation is demonstrated within the ABF₃ fluoride perovskites. Such tailoring promotes distinct near-infrared photoluminescence through antiferromagnetic super-exchange across effective dimers. The crossover dopant concentrations for the occurrence of Mn²⁺ interaction within the first and second coordination shells comply well with experimental observations of concentration quenching of photoluminescence from isolated Mn²⁺ and from Mn²⁺-Mn²⁺ effective dimers, respectively. Tailoring of this procedure is achieved via adjusting the Mn-F-Mn angle and the Mn-F distance through substitution of the A⁺ and/or the B²⁺ species in the ABF₃ compound. Computational simulation and X-ray absorption spectroscopy are employed to confirm this. The principle is applied to produce pure anti-Stokes near-infrared emission within the spectral range of ≈760-830 nm from codoped ABF₃:Yb³⁺,Mn²⁺ upon excitation with a 976 nm laser diode, challenging the classical viewpoint where Mn²⁺ is used only for visible photoluminescence: in the present case, intense and tunable near-infrared emission is generated. This approach is highly promising for future applications in biomedical imaging and labeling.

Abnormal luminescent property of Mn2+ in α-LiZnBO3:Mn2+

The abnormal red-emitting luminescent property of tetrahedrally coordinated Mn²⁺ in α-LiZnBO₃ is observed.

Oxonitridosilicate Y10(Si6O22N2)O2:Ce3+,Mn2+ phosphors: a facile synthesis via the soft-chemical ammonolysis process, luminescence, and energy-transfer properties

Ce(3+)- and/or Mn(2+)-activated Y10(Si6O22N2)O2 phosphors have been prepared via a soft-chemical ammonolysis method. Structure refinement, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared, and thermogravimetry analysis have been employed to characterize the phase purity, crystal structure, morphology, crystallization condition, chemical composition, and thermal stability of the products. The photoluminescence and cathodoluminescence properties for Ce(3+)- and Mn(2+)-doped Y10(Si6O22N2)O2 phosphors were studied in detail. For Ce(3+)/Mn(2+) singly doped Y10(Si6O22N2)O2 phosphors, typical emissions of Ce(3+) (blue) and Mn(2+) (reddish-orange) ions can be observed. Especially, Ce(3+) emission at different lattice sites 4f and 6h has been identified and discussed. Energy transfer from Ce(3+)(I) and Ce(3+)(II) to Mn(2+) ions in Y10(Si6O22N2)O2:Ce(3+),Mn(2+) samples has been validated and confirmed by the photoluminescence spectra and luminescence decay times. A color-tunable emission in Y10(Si6O22N2)O2:Ce(3+),Mn(2+) phosphors can be achieved by an energy-transfer process and a change in the doping concentration of the activators. The temperature-dependent photoluminescence properties and degradation property of cathodoluminescence under continuous electron bombardment of as-synthesized phosphors prove that the Y10(Si6O22N2)O2 host has good stability. Therefore, the Y10(Si6O22N2)O2:Ce(3+),Mn(2+) phosphors may potentially serve as single-phase blue/reddish-orange phosphors for white-light-emitting diodes and field-emission displays.