Luminescence Enhancement of Mn4+-Activated Fluorides via a Heterovalent Co-Doping Strategy for Monochromatic Multiplexing

Novel green/red oxyfluoride phosphors with excellent optical properties for near-UV excited white light emitting diode

Novel eye-sensitive Ba3Nb2O2F12(H2O)2:Tb3+ green and Ba3Nb2O2F12(H2O)2:Mn4+ red oxyfluoride phosphors with extremely strong absorption in the UV region were designed and synthesized by simple co-precipitation strategy. Particularly, Tb3+ ions were doped in this matrix for the first time, which greatly improves their absorption efficiency in the near ultraviolet region (367 nm) and emits sharp green light (544 nm). In addition, the Ba3Nb2O2F12(H2O)2:Mn4+ red phosphors have strong zero phonon line (ZPL) emission at 625 nm, which is conducive to improving the sensitivity of human eye and color purity. Meanwhile, the optical properties of the red phosphor are significantly enhanced via doping K+ cations as charge compensators. Crystal field environment and nephelauxetic effect of the as-prepared phosphors before and after K+ cation doping were systematically analyzed. Moreover, these synthesized red/green phosphors have good thermal stability and moisture resistance. Remarkably, the as-prepared Ba3Nb2O2F12(H2O)2:5%Mn4+ or K0.9Ba2.1Nb2O2F12(H2O)2:5%Mn4+ red phosphors can be directly mixed with the as-synthesized Ba3Nb2O2F12(H2O)2:13%Tb3+ green phosphor coating on 365 nm near-ultraviolet LED chip to package WLED devices with excellent electroluminescence performance. These findings are conducive to opening an avenue for screening the unique structure of optical materials.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Optical enhancement of highly efficient organic-inorganic oxyfluoride red phosphors via the cation co-doping strategy

Herein, a new organic cationic matrix [N(CH3)4]3MoO3F3 suitable for Mn4+ doping was constructed. Due to the large steric hindrance of N[CH3]4+ (TMA), charge compensation defects can be effectively prevented in the heterovalent Mn4+-doping process, and a high IQE (91.05%) was obtained. Through the cation co-doping strategy, Mg2+/Zn2+/Li+ cations were introduced into the Mo6+ cationic site, which improved the crystallinity of the matrix and reduced energy losses, so as to improve luminescence intensity, QE, thermal stability, water stability and other spectral properties. Meanwhile, [N(CH3)4]2TiF6:Mn4+ phosphors with the same TMA organic cation and equivalent Mn4+ doping were synthesized for comparison, and the effects of the Mg2+ cation co-doping strategy on the spectral properties of phosphors with different matrix types (fluoride/oxyfluoride) and substitution types (equivalent/non-equivalent) were analyzed. These findings provide the basis for the preparation of new luminescent materials. Furthermore, according to the optical properties exhibited by these phosphors, they are packaged into WLED devices with excellent photoelectric properties, which are suitable for indoor lighting and display fields.

Mn-Activated Fluoride Phosphors Modified by Surfactant with Outstanding Water Resistance and Luminescent Thermal Properties

Although Mn⁴⁺-activated fluoride phosphors have high luminescence quality, their poor water resistance and thermal fluorescence properties significantly limit their practical applications. Here, we propose a surfactant modification strategy by adding the surfactant cetyltrimethylammonium bromide (CTAB) to the synthesis and modifying the surface of the phosphor with ethylene diamine tetraacetic acid (EDTA) to obtain a phosphor with excellent luminescence thermal properties and water resistance, K₂TiF₆:Mn⁴⁺-xCTAB-EDTA (KTFM-xC-E) phosphors. The experimental and X-ray diffraction Rietveld refinement results confirm that the phosphor has higher structural rigidity and thus improved thermal stability. The surface modification with EDTA resulted in the formation of a dilute Mn⁴⁺ shell layer on the phosphor surface, which prevented the inward hydrolysis of the phosphor and resulted in excellent water resistance. Therefore, we have successfully modified K₂TiF₆:Mn⁴⁺ (KTFM) phosphors using low-cost surfactants, which also provides new ideas for other commercial high-quality phosphors.