Symmetry and singular site-occupancy-controlled strong near-narrow-band cyan emission from Ca3Xn2Ge3O12:Bi3 + (Xn = Sc, Y, Lu) phosphors for healthy WLED lighting
The advancement of narrow-band cyan-emitting phosphors activated by near-ultraviolet LED chips is crucial for creating high-efficiency, health-promoting WLED lighting. Guided by a single and symmetrical crystallographic site, a near-ultraviolet excitation, near-narrow-band, and thermally stable cyan light emission was achieved from Bi 3+ -activated garnet-structured Ca 3 Xn 2 Ge 3 O 12 :Bi 3+ (Xn = Sc, Y, Lu). When incorporated into WLEDs, the color rendering index (CRI) of devices containing Ca 3 Sc 2 Ge 3 O 12 :Bi 3+ cyan phosphor reaches 92.8, indicating potential value for healthy lighting applications. Furthermore, by integrating spectral and crystallographic data with empirical formula calculations, a comprehensive analysis of the luminescence behavior among the three Ca 3 Xn 2 Ge 3 O 12 :Bi 3+ (Xn = Sc, Y, Lu) phosphors were performed. This analysis was designed to elucidate the similarities and differences in their luminescence properties, as well as to uncover the underlying mechanisms responsible for the near-narrow-band emission of Bi 3+ . The results indicate that under the combined influence of factors volume polarization, fractional covalency, and charge of the anions, Ca 3 Xn 2 Ge 3 O 12 :Bi 3+ (Xn = Sc, Y, Lu) exhibits the same strongest excitation peak. However, due to variations in Stokes shift and bandgap, the three phosphors exhibit distinct emission peaks and thermal quenching properties. This study aims to establish fundamental principles for the development of Bi³ ⁺-activated narrow-band emission phosphors.
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