Development of NaY9Si6O26:Yb3+ Phosphor with High Thermal Stability and Its Crystals Structure and Luminescent Properties for NIR Anti-Counterfeiting

Abstract

Near-infrared (NIR) radiation has attracted considerable industrial and research interest. NIR emission has promising potential for varied applications, mostly related to the characterization of chemicals, security, pharmaceutical, medical, cosmetic, food, and agricultural industries, which contribute to the advancement of modern technology. Emission sources such as tungsten halogen lamps, light emitting diodes (LEDs) and phosphor converted LEDs (pc-LEDs) can emit in the infrared range. Among these, NIR pc-LED is considered as the most suitable emission source because it provides adequate emission, high efficiency, long lifetime and excellent durability. In recent years, studies have been conducted to adjust the emission spectrum suitable for NIR phosphors and to improve quantum efficiency in order to apply them to advanced applications and devices of pc-LEDs.Recently, it is necessary to develop a material capable of specifying the near-infrared emission wavelength of near-infrared excitation beyond ultraviolet excitation infrared for advanced anti-counterfeiting against advanced counterfeiting technology. In the present study, a rare-earth-containing compound doped with an activator was used as a host system for a near-infrared phosphor to develop suitable luminescent properties. Yb3+-doped NaY9Si6O26 phosphors were synthesized using a conventional solid-state reaction method. The main phase of the synthesized phosphor samples exhibited a hexagonal structure NaY9Si6O26 phase, and had an angular-shape with an average grain size of 1-3 μm. The NaY9Si6O26:Yb3+ phosphors showed a broad near-infrared emission from 950 to 1100 nm, which was attributed to the 2F5/2 → 2F7/2 transition of Yb3+ ions under 270 and 920 nm excitation. The excitation spectra, recorded by monitoring the emission at 985 nm, showed two bands in the ultraviolet and infrared regions The excellent thermal stability of NaY9Si6O26:Yb3+ phosphor was evident from the fact that the relative PL intensity of NaY9Si6O26:Yb3+ phosphor was 82% of the initial PL intensity at 300 °C, and the thermal degradation was negligible after cooling. These results suggest NaY9Si6O26:Yb3+ phosphors are promising next-generation candidates for advanced anti-counterfeiting applications.