In this study, the NaAg 1-x Bi x/3 MoO 4 (x = 0.06, 0.12, 0.18, and 0.24) ceramics were successfully synthesized via solid-state reaction at 400–535 °C. Notably, the NaAg 0.82 Bi 0.06 MoO 4 ceramic exhibited exceptional dielectric properties at 450 °C (ε r = 7.39 ± 0.05, Q × f = 18,867 ± 1480 GHz, τ f = −84.8 ± 1.3 ppm/°C). The Rietveld refinement confirmed its spinel-like structure belonging to the Fd-3m (227) space group, along with the formation of a Na 0.5 Bi 0.5 MoO 4 secondary phase, as supported by SEM and EDS analyses. Further investigation revealed that the Na 0.5 Bi 0.5 MoO 4 phase adversely impacted the Q × f value, while the relative density positively correlated with Q × f. Based on the Shannon additivity rule, the contribution of Bi 3+ ions to ε r was elucidated. The P–V-L theory provided a theoretical foundation for understanding the dielectric behavior of NaAg 1-x Bi x/3 MoO 4 ceramics. Additionally, Raman spectroscopy directly confirmed the enhancement of molecular polarizability by Bi 3+ ions and disclosed a negative correlation between the A 1g vibration mode and Q × f, further elucidating the intimate link between internal lattice vibrations and microwave dielectric properties.
Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are promising for many applications in non-destructive testing, bio-imaging, and modern agriculture. However, developing self-activated NIR phosphors with high efficiency and excellent thermal stability is a great challenge for current research. In this work, a self-activated far-red to NIR emitting NaLaMgWO 6 phosphor is prepared by the high-temperature solid-state reaction method, whose luminescence properties are investigated in detail. In addition, the introduction of Bi 3+ ions as sensitizers enhances the emission intensity of far-red to NIR light (650-850 nm) through a Bi 3+ → WO 6 6– energy transfer design strategy, resulting in an increased internal quantum efficiency (IQE) from 56.4% to 64.8% and thermal stability from 54% to 72% (420 K). Finally, the combination of NaLaMgWO 6 :Bi 3+ with 365/460 nm commercial LED chip is prepared into NIR pc-LED devices, demonstrating satisfactory performance in the field of night vision detection and other wide range of practical applications.
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