Utilizing energy transfer strategy to produce efficient green luminescence in Ca2LuHf2Al3O12:Ce3+,Tb3+ garnet phosphors for high-quality near-UV-pumped warm-white LEDs
White light-emitting diodes (LEDs) are widely used in lighting and display devices, and the exploration of phosphors with excellent luminescence performance and good stability is the key to the development of white LEDs. In this work, we reported novel near-UV-excited green-emitting Ca 2 LuHf 2 (AlO 4 ) 3 :Ce 3+ ,Tb 3+ garnet phosphors with efficient Ce 3+ → Tb 3+ energy transfer. The CLHA:Ce 3+ ,Tb 3+ green phosphors were successfully synthesized by a high-temperature solid-state method, and the phosphors were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence excitation and photoluminescence spectra, the Commission International de I’Eclairage (CIE) chromaticity coordinates, quantum efficiency and temperature-dependent emission spectra. Due to the spin-allowed 4f → 5d transition of Ce 3+ ions, the CLHA:Ce 3+ ,Tb 3+ phosphors exhibited a strong broad excitation band in the 300–470 nm near-ultraviolet (near-UV) range. Under 408 nm excitation, the CLHA:Ce 3+ ,Tb 3+ phosphors showed strong green light with emission center at 543 nm. The mechanism of energy transfer from Ce 3+ to Tb 3+ ions was attributed to quadruple-quadruple interaction. Impressively, the internal quantum efficiency and external quantum efficiency of the optimal CLHA:0.02Ce 3+ ,0.5Tb 3+ green phosphors were measured to be 77.1% and 55.8%, respectively. Finally, using the CLHA:0.02Ce 3+ ,0.5Tb 3+ phosphors as green-emitting color converter, a near-UV-pumped white LED device was fabricated, and under 80 mA driving current the LED device demonstrated bright warm-white light with high color rendering index (93.7), low correlated color temperature (3574 K), CIE chromaticity coordinates (0.3922, 0.3633), and high luminous efficacy (29.35 lm/W).
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