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In order to obtain novel and more efficient red light-emitting materials, a series of Sr 2 [Mg 1-x Li x Al 5-x Si x N 7 ] : 0.01Eu 2+ (SMAN-xLS, 0≤x≤0.5) red phosphors were devised and successfully synthesized via the high temperature solid state reaction and the effects of the co-substitution of [Mg-Al] 5+ by [Li-Si] 5+ on structural and luminescence properties is investigated in detail. A series of powder XRD data and Rietveld refinement indicate that [Li-Si] 5+ co-substitution can successfully enter the Sr 2 [MgAl 5 N 7 ] : 0.01Eu 2+ (SMAN) lattice. With the entry of [Li-Si] 5+ into the lattice, the substitution of Al 3+ by Si 4+ leads to the weakening of the nephelauxetic effect of the 5d level of Eu 2+ , which shifts the emission peak from 657 nm to 647 nm and reduces the excitation in the green region, i.e., lowers the absorption of green light. When the amount of [Li-Si] 5+ co-substitution is x=0.1, the luminescence intensity and thermal stability of the sample are enhanced, in which the external quantum efficiency (EQE), reflecting the luminescence intensity, is elevated by 49.6 %. The increase in lattice rigidity gives rise to higher luminescence intensity, and the introduced trap levels for the compensation of luminescence enhances the thermal stability. Under blue laser excitation, the SMAN-0.1LS can achieve an ultra-high luminescence saturation threshold of 52.22 W/mm 2 , which is remarkably superior to other existing red phosphors, a breakthrough performance that has enormous potential for application in high-power laser display light sources. Cathodoluminescence (CL) characterization and measurements attest to the favorable CL properties of SMAN-0.1LS. By measuring the pressure-dependent luminescence of SMAN-0.1LS, the emission peak can be shifted from 650 nm to 702 nm with the increase of pressure, and the sensitivity dλ/dP is 5.07 nm/GPa, which is indicative of the potential application of this system as an optical pressure sensor., (© 2024 Wiley-VCH GmbH.)

Conventional optical anti-counterfeiting strategies are based on the single-color emission, which are easily deciphered and thus greatly limited in the application of information security. Herein, a multimodal dynamic optical information coding with red, green, and blue (RGB) tricolors has been developed by photoluminescence (PL), persistent luminescence (PersL), thermally stimulated luminescence (TSL), and thermally stimulated persistent luminescence (TSPL). The BaSi 2 O 2 N 2 :Eu 2+ phosphors with a blue emission peak at 494 nm were used as the crucial blue optical information coding material and exhibited the distinctive response properties to light, heat, and force stimuli with intrinsic trap depths of 0.674 and 0.82 eV. More importantly, by combining the red Sr 2 Si 5 N 8 :Eu 2+ ,Dy 3+ and green SrSi 2 O 2 N 2 :Eu 2+ ,Dy 3+ nitride phosphors, a RGB tricolor and multimodal strategy has been successfully developed for anti-counterfeiting applications. The "RGB tricolor flower" with RGB emissions is given as a typical example to achieve the dynamic display of optical information encryption and decoding through the various PL, PersL, TSL, and TSPL modes. Finally, the traditional quick response (QR) code mechanism has been integrated into the design of multi-information encrypted RGB tricolor anti-counterfeiting devices with different identifiabilities of the encrypted information in natural light, PL, PersL, TSL, and TSPL modes. The laminated layers of RGB QR code patterns containing different specific information, such as "DLPU" and "116034", can be effectively recognized in the corresponding modes. The design strategy of RGB tricolor and multimodal optical information encryption and decoding devices in this work greatly improves the security level of advanced optical information technologies and extends the potential applications in dynamic anti-counterfeiting fields.

The systematic substitution of Ba in the Sr site of Sr[Mg 2 Al 2 N 4 ]:Eu 2+ generates a deep-red-emitting phosphor with enhanced thermal luminescence properties. Gas pressure sintering (GPS) of all-nitride starting materials in Molybdenum (Mo) crucibles yields pure-phase red-orange-colored phosphors. Peaks in the synchrotron X-ray diffraction (SXRD) data show a systematic shift toward smaller angles due to the introduction of the larger Ba cation in the same crystal structure. The photoluminescence property reveals that Ba substitution shifts the original emission wavelength of Sr[Mg 2 Al 2 N 4 ]:Eu 2+ (625 nm) toward ∼690 nm for Ba[Mg 2 Al 2 N 4 ]:Eu 2+ . Thermal stability measurement of Sr 1- x Ba x [Mg 2 Al 2 N 4 ] indicates a systematic increase in stability from x = 0 to x = 1. X-ray absorption near-edge spectroscopy (XANES) results demonstrate the coexistence of Eu 2+ and Eu 3+ . The red-shift and the enhanced thermal stability reveals that the distance of the emitting 5 d level to the conduction band of Ba[Mg 2 Al 2 N 4 ]:Eu 2+ is large. The ionic size mismatch of Eu occupying a Ba site reduces the symmetry, thereby further splitting the degenerate emitting 5 d level and lowering the energy of the emitting center. The development of deep-red phosphors emitting at 670-690 nm ( x = 0.8-1.0) offers possible candidates for plant lighting applications.

Effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN₃:Eu 2+ phosphor (CASIN) were investigated by a combustion synthesis method. Ca, Al, Si, Eu₂O₃, NaN₃, NH₄Cl and Si₃N₄ powders were used as the starting materials and they were mixed and pressed into a compact which was then wrapped up with an igniting agent ( i.e ., Mg + Fe₃O₄). The compact was ignited by electrical heating under a N₂ pressure of ≤1.0 MPa. By keeping the molar ratios of Al and Si (including the Si powder and the Si in Si₃N₄ powder) both at 1.00 and that of Eu₂O₃ at 0.02, XRD (X-ray diffraction) coupled with TEM-EDS (transmission electron microscope equipped with an energy-dispersive X-ray spectroscope) and SAED (selected area electron diffraction) measurements show that AlN:Eu 2+ and Ca-α-SiAlON:Eu 2+ are formed as the major phosphor products when the Ca molar ratio (denoted by Y ) is equal to 0.25 and AlN:Eu 2+ and Ca-α-SiAlON:Eu 2+ could not be detected at Y ≥ 0.75 and ≥1.00, respectively. CASIN ( i.e ., CaAlSiN₃:Eu 2+ ) becomes the only phosphor product as Y is increased to 1.00 and higher. The extent of formation of CASIN increases with increasing Y up to 1.50 and begins to decrease as Y is further increased to 1.68. While the excitation wavelength regions are similar at various Y , the emission wavelength regions vary significantly as Y is increased from 0.25 to 1.00 due to different combinations of phosphor phases formed at different Y . The emission intensity of CASIN was found to vary with Y in a similar trend to its extent of formation. The Ca and Eu contents (expressed as molar ratios) in the synthesized products were found to increase roughly with increasing Y but were both lower than the respective Ca and Eu contents in the reactant mixtures.