Hybrid Carbon Quantum Dot/NaBiF₄:Eu^3<b>+</b> Nanophosphors for White Light-Emitting Diode

In this study, we synthesize and characterize photoluminescent carbon quantum dots (CQDs) and Eu3+-doped NaBiF4 nanophosphors to develop efficient white light-emitting diodes (WLEDs). Blue and green CQDs are prepared using microwave-assisted methods with citric acid and nitrogen-based precursors, exhibiting strong excitation-dependent emission with peak maxima at 458 and 526 nm, respectively. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) confirm the presence of surface functional groups and nanoscale size, which are both critical for quantum confinement and optical tuning. Simultaneously, NaBi(1–x)F4:xEu3+ (x = 0.01–0.5 mmol) nanophosphors are synthesized via a simple solution process method. Structural analyses confirm the preservation of the hexagonal phase with successful Eu3+ substitution, as validated by XRD, SAED, and XPS. Photoluminescence measurements reveal intense red emission centered at 615 nm, with optimal doping at 20% Eu3+. Time-resolved PL shows a decay lifetime of up to 6.2 ms, indicating efficient radiative recombination. The integration of CQDs and nanophosphors onto a UV LED (375 nm) results in a white emission with CIE coordinates (0.26, 0.32), and a color rendering index (CRI) of 81. These results demonstrate the synergistic potential of CQDs and rare-earth phosphors in creating tunable, efficient, and stable WLEDs for advanced lighting applications.