Mn⁴⁺ activated Al₂O₃ red-emitting ceramic phosphor with excellent thermal conductivity

Current research on phosphor materials for LED applications often focuses on improving luminescence efficiency and thermal stability. While many phosphors are available, their performance under high temperatures and their compatibility with UV/blue excitation remain key challenges. Prior research has shown that aluminum oxide hosts can support Mn4+ luminescence, but the impact of sintering atmosphere on optical properties is not fully understood. The crystal field effects and nephelauxetic interactions in Mn4+ doped systems are also areas of ongoing investigation. No prior work had resolved the combined influence of crystal field strength and thermal conductivity on Mn4+ emission in Al2O3 ceramics. This gap motivated the current study to explore the synthesis and characterization of Al2O3:Mn4+, Mg2+ phosphor under controlled conditions. Researchers aim to clarify how sintering environment affects optical transmittance and luminescence intensity. Understanding these factors can guide the development of phosphors suitable for high-performance LED applications. The study also seeks to quantify the relationship between crystal field parameters and emission properties in this system.

The study aimed to synthesize and characterize an Al2O3:Mn4+, Mg2+ red-emitting ceramic phosphor suitable for LED applications. Researchers focused on the influence of sintering atmosphere on optical and structural properties. They sought to determine whether oxygen or air sintering produces better luminescence and transmittance. The study also aimed to calculate crystal field and nephelauxetic parameters to explain Mn4+ emission behavior. Another goal was to measure quantum yields under UV and blue excitation to assess efficiency. Researchers wanted to evaluate the thermal conductivity of the material for practical use in high-power LEDs. The study also aimed to measure the density of the phosphor using the Archimedes method. The ultimate objective was to identify a phosphor with both strong red emission and high thermal stability for LED integration.

The researchers used a solid-state reaction method to synthesize Al2O3:Mn4+, Mg2+ phosphor. They sintered the material in both oxygen and air atmospheres to compare properties. Optical transmittance and luminescence intensity were measured for each sample. Crystal field parameters were calculated using spectroscopic data. Researchers applied the Racah model to determine B and C values for Mn4+ ions. The nephelauxetic ratio β1 was also calculated to assess electron interactions. Quantum yields were measured under 395 nm and 460 nm excitation sources. Density was determined using the Archimedes method for physical characterization. Thermal conductivity was measured at 30 °C to assess material performance under typical operating conditions.

The Al2O3:Mn4+, Mg2+ phosphor sintered in oxygen showed higher optical transmittance than the air-sintered sample. The oxygen-sintered material also exhibited stronger luminescence intensity, making it more suitable for LED use. Calculated Dq/B ratio was 1.74, indicating a weak crystal field for Mn4+ ions in the host. This value was lower than the 2.2 threshold for stronger crystal fields. Quantum yields were 46% under 395 nm and 28.7% under 460 nm excitation. The measured density was 3.61 g/cm³ using the Archimedes method. The material showed a thermal conductivity of 26.27 W·m⁻¹·K⁻¹ at 30 °C. These results suggest the phosphor combines good optical and thermal properties for LED applications.

The study demonstrated that oxygen sintering enhances the optical performance of Al2O3:Mn4+, Mg2+ phosphor. The weak crystal field environment, as shown by the Dq/B ratio, supports efficient Mn4+ emission. The high thermal conductivity of 26.27 W·m⁻¹·K⁻¹ at 30 °C makes the material suitable for high-power LED applications. The measured quantum yields under 395 nm and 460 nm excitation suggest practical utility in LED lighting systems. The density of 3.61 g/cm³ indicates good structural integrity of the ceramic. The combination of optical and thermal properties positions this phosphor as a viable candidate for LED integration. The study also highlights the importance of sintering atmosphere in phosphor performance. These findings align with the authors' goal of developing a phosphor with both strong red emission and high thermal stability.