Graphical Catching the rays : Nitrogen doping is an efficient approach to endow the wide-band-gap semiconductor Sr 4 Nb 2 O 9 with visible-light responses. Efficient photocatalytic oxygen production from water is achieved with this N-doped Sr 4 Nb 2 O 9 under visible-light illumination, which is influenced strongly by synthetic conditions. DFT calculations reveal the critical role of nitrogen, which forms additional energy levels within the band gap of Sr 4 Nb 2 O 9 . Photocatalytic water splitting is an appealing process for solar energy conversions yet it is often limited by the slow oxidation of water to oxygen half-reaction. Here we performed an investigation on N-doped Sr 4 Nb 2 O 9 as a water oxidation photocatalyst. Our results show that N doping is an effective approach to improve the visible-light response of Sr 4 Nb 2 O 9 . Efficient photocatalytic oxygen production was observed after N doping, and the highest production rate of ∼27 μmol h −1 under visible-light irradiation corresponds to an apparent quantum efficiency of ∼0.31 %. Clear anodic photocurrent can be generated under visible-light illumination, and the flat-band potential was determined to be ∼−1.25 V vs. Ag/AgCl at pH 7. Theoretical calculations reveal that N doping introduces additional valence bands and is responsible for the visible-light response. Variations in light absorption and photo-oxidation performance can be controlled by modifying these valence band positions using different nitridation temperatures.
Yan Tingting,Sun Lei,Xi Dongyang,Jin Dinghan,Li Han,Liu Linan
This study reports the successful synthesis of Sr₄Nb₂O₉:xHo³⁺ (x = 0.005–0.04) green phosphors by molten salt method. Unlike conventional solid-state synthesis (1350 °C for 7 h), this method reduces the reaction temperature to 1100 °C and decreases processing time to 5 h, yielding products with regular platelet morphology. Comprehensive structural, morphological, and optical characterizations were performed through X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The Sr₄Nb₂O₉:0.02Ho³⁺ phosphor exhibits a strong green emission peak at 530 nm under 460 nm excitation. The optimal doping concentration was determined to be 0.02 mol, with concentration quenching attributed to primarily mediated by dipole-dipole (d-d) interactions. The chromaticity coordinates (0.295, 0.696) indicate high color purity (99.5%) and a correlated color temperature (CCT) of 6033 K. High-pressure Raman experiments show that Sr₄Nb₂O₉ remains structurally stable up to 15.3 GPa. High-pressure fluorescence experiments reveal that the Sr₄Nb₂O₉:0.02Ho³⁺ phosphor maintains 58% of its ambient-pressure fluorescence intensity even at 18.2 GPa. Furthermore, at 448 K, the phosphor retains 86.8% of its room-temperature fluorescence intensity. The quantum yield of the Sr₄Nb₂O₉:0.02Ho³⁺ phosphor reached 23.6%. These findings suggest Sr₄Nb₂O₉:Ho³⁺ phosphors may be potential candidates for solid-state lighting applications in high-pressure environments. Graphical
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