Two new metal aluminium phosphate millimetre-crystals NaBa 2 Al(P 2 O 7 ) 2 and NaBaAl(PO 4 ) 2 were successfully grown by using high-temperature molten method. The crystals NaBa 2 Al(P 2 O 7 ) 2 and NaBaAl(PO 4 ) 2 are located in space groups P ¯1 and P 2 1 /c, respectively. NaBa 2 Al(P 2 O 7 ) 2 displays a [Al(P 2 O 7 ) 2 ] 1D chain structure constructed from corner-sharing linkage of novel AlP 4 O 16 9− anion groups, and the AlP 4 O 16 9− group is formed by edge-sharing connection of two P 2 O 7 dimers and one AlO 6 octahedron . However, NaBaAl(PO 4 ) 2 exhibits a new [Al(PO 4 ) 2 ] 2D layer structure composed of AlP 2 O 10 7− anion groups via corner-sharing, and the AlP 2 O 10 7− group is generated by alternate linkages of corner-sharing PO 4 and AlO 4 tetrahedra. Analysis based on Pauling's electrostatic rule and Brown's bond valence model finds that structural feature of the two anion groups is mainly responsible for their different dimension structures in addition to structure-directed role of large Ba 2+ . The two crystals manifest a deep-UV optical transparency below 190 nm and good thermal stability, making them a potential optical window material. First-principles calculations reveal that the optical bandgaps of both crystals are determined by the Ba–O groups, rather than Al–O and P–O common groups.
White light-emitting diodes (WLEDs) play a crucial role in solid-state lighting technologies. Among the key factors contributing to their performance, the development of high-quality cyan phosphors is critical in achieving excellent color rendering index (CRI) and stable long-term operation. In this study, a cyan-emitting phosphor, NaBa 2 Al(P 2 O 7 ) 2 : x Eu 2+ ( x = 0.01-0.06), was explored. The material's structures, morphology, optical behavior, and thermal stability were analyzed. Rietveld refinement reveals that the phosphor exhibits high crystallinity and confirms the successful substitution of Eu 2+ ions into Ba 2+ sites within the crystal lattice. Upon excitation at 320 nm, the phosphor emits broad, asymmetric cyan light, with peak intensity occurring at an Eu 2+ concentration of 0.03 achieving internal quantum efficiency (IQE) of 68.9%. Energy transfer and Gaussian fitting analyses show that Eu 2+ ions occupy two distinct crystallographic sites, and concentration quenching is attributed to dipole-dipole interactions. The phosphor retains 77% of its intensity at 425 K, with an activation energy of 0.3173 eV, demonstrating high thermal stability and color consistency. When integrated with a red-emitting phosphor onto a 320 nm UV chip, a white light-emitting diode (WLED) is fabricated, exhibiting a correlated color temperature (CCT) of 5727 K and a color rendering index (CRI) of 95.6. These results highlight this phosphor for applications in advanced white light-emitting diode (WLED) technologies across diverse lighting systems.
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