Phase Evolution and Emission Behaviour of Dual Precipitants Derived Y-Al-B-O-Based Luminescent Materials

Abstract

Luminescent materials based on oxides and borates, such as yttrium aluminium garnet (YAG) and yttrium borate (YBO3), are indispensable for advanced applications due to their robust chemical stability and high luminescence efficiency. Ce-doped YAG emits yellow light, essential for enhancing white LED technology. YBO3 is renowned for its UV absorption capability and thermal and chemical stability, making it highly suitable for demanding environments. Cerium-doped YBO3 phosphors emit blue light and offer high tunability for applications spanning LEDs, flat displays, and optoelectronic devices. The synergistic combination of these materials optimizes color emission properties, significantly enhancing their versatility across a wide range of luminescent applications. This study focuses on advancing Ce-based Y-Al-B-O-based luminescent materials through innovative synthesis methods, particularly using dual precipitating reagents, i.e., boron-containing sodium borohydride (SB) and hydroxide-containing ammonia solution. These reagents enable precise control over phase formation, which is crucial for developing advanced luminescent materials tailored for applications in lighting and displays. Several characterizations were carried out using these calcined powders, including XRD, FTIR, Raman, FESEM, EDX mapping, photoluminescence spectra, CIE color coordinates, CCT, lifetime, electroluminescence, and quantum yield. Based on this concept, this research is focused on developing phase evolution and emission behavior of dual precipitants-derived Y-Al-B-O-based luminescent materials by varying boron-containing precipitants, cerium content, and calcination temperatures. Depending on calcination temperatures, distinct phases were produced, and the variations of the emission intensity of blue and yellow-green allowed the production of tunable color- emitting materials, including white emission, which is essential for achieving high-quality lighting and display functionalities. Borate, mixed borate-oxide, and oxide-based phases have been derived via different synthesis methods, such as gelation and precipitation. For the gelation-precipitation method, white emission was achieved at 1500°C 6h, which was reduced to 1h holding time for the precipitation method by reducing the boron-containing precipitant, i.e., SB. Further, optimizing the SB volume and varying the cerium concentration is crucial to studying their effects on emission behavior. With optimized SB volume to 10ml, samples calcined at 1000°C and 1200°C produced primary YAG with secondary YBO3 and Al2O3, which produced tunable emissions, including near white at reduced calcination temperature. Moreover, increasing cerium concentration from 2-8 mol% shifted emission peaks from blue to yellow-green. The optimal cerium concentration was 6 mol%, producing near-white emissions suitable for various luminescent applications. Additionally, with the optimized cerium concentration, further synthesis was conducted with reduced SB volumes from 8ml-2ml, examining the effects on phase evolution and emission behavior. Lower SB amounts resulted in primary YAG with secondary YBO3 at 1000°C and 1200°C. The emission spectra of the calcined samples with variable lowered SB volumes showed tuning of emission colors, covering blue, yellow-green, and near white. The samples with 6 mol% Ce-based YAG powder prepared with 6 ml SB calcined at 1000°C successfully produced white light when encapsulated over a blue LED. Dual precipitants by varying SB amounts followed by ammonia solution may be a unique approach for developing Y-Al-B-O-based luminescent materials for various lighting applications, including white light generation.