Integration of rare earth activated phosphor into inorganic glass: from bulk phosphor in glass to phosphor-glass thin films

Light-emitting diodes (LEDs) have transformed the lighting industry owing to their energy efficiency, long lifespan, and design flexibility. However, the performance of commercially available LEDs is often hindered by the use of organic binders that encapsulate phosphor powders. These binders tend to degrade over time, resulting in reduced luminous efficacy and colour shifts. To address these limitations, phosphor-in-glass (PiG) composites have emerged as a promising alternative. PiGs are typically fabricated by mixing phosphor powders with glass frit and sintering the mixture at an optimal temperature to form a stable, inorganic matrix. Following the successful incorporation of YAG:Ce³⁺ into a glass matrix by Y.K. Lee et al. [1], a wide range of phosphors have since been investigated for PiG fabrication [2,3]. Building on this foundation, we explored the incorporation of luminescent phosphors into inorganic glasses based on borosilicate and tellurite, selected for their excellent chemical durability and thermal stability[4]. We adopted a low-temperature melt-quenching technique to embed the phosphors into the glass matrix. Tellurite-based glasses, in particular, proved to be highly suitable hosts for the phosphors due to their relatively low melting temperatures—which help minimize phosphor degradation—and their favourable refractive index compatibility with phosphors. The structural and microscopic characteristics of the resulting PiG composites were thoroughly examined using electron microscopy, supported by elemental mapping, confirming successful incorporation of phosphors within the glass matrix. Despite successful synthesis and promising stability, challenges such as non-uniform phosphor distribution and a limitation in phosphor content (up to 20 wt%) affect the performance of bulk PiG materials. To address these drawbacks, we developed a novel thin-film “sandwich” architecture, embedding phosphor layers between a silica substrate and a tellurite glass coating achieved by the femtosecond pulsed laser deposition technique. This method not only ensures better diffusion and encapsulation of phosphor films but also significantly enhances luminescence efficiency. Our findings highlight the potential of these phosphor-glass films as robust, high-efficiency inorganic colour converters for next-generation lighting and display applications.