Runtian Kang,Hang Chen,Ruijie Ji,Haoyang Wang,Takatoshi Seto,Yuhua Wang
It is of great significance for white light-emitting diodes (wLEDs) to explore new, efficient and stable inorganic phosphors excited by wideband near-ultraviolet (n-UV) light. A new type of efficient emission-tunable Ce3+/Mn2+ doped Ca2YHf2Al3O12 (CYHAO) garnet phosphor which can be excited by n-UV light is studied in this work. Due to the effective energy transfer (ET) from Ce3+ to Mn2+ in CYHAO, CYHAO:0.09Ce3+,xMn2+ phosphors have a wide excitation band in the 370–470 nm region with a peak at 410 nm. Under excitation at 410 nm, all the samples show tunable color emission and match with the near UV chip. Through the decay time, it is determined that the energy transfer efficiency is as high as 88.83%. The calculated activation energy is about 0.217 eV, indicating the relatively good thermal stability. The cathodoluminescence (CL) properties show that the phosphor has a high saturation current and saturation voltage. A single component white LED is fabricated by using the CYHAO:0.09Ce3+,0.3Mn2+ phosphor and a 400 nm n-UV chip. It is worth noting that the detailed study of the energy transfer mechanism, thermal quenching mechanism and CL mechanism has reference value for the development of new co-doped phosphors.
Inorganic phosphors with broadband near-ultraviolet (near-UV) excitation and efficient visible emission are highly important for fabricating high-performance near-UV-pumped white light-emitting diodes (LEDs). Herein, we report on novel efficient near-UV-excitable Ce3+/Tb3+ ion co-activated Ca2YHf2Al3O12 (CYHA) green-emitting garnet phosphors, which were successfully prepared through a high-temperature solid-state reaction process. X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence, CIE color coordinates, the internal and external quantum efficiency, and temperature-dependent emission spectra were used to characterize the samples. Interestingly, due to the efficient energy transfer from Ce3+ to Tb3+ ions in CYHA, the CYHA:Ce3+,Tb3+ samples presented a wide excitation band in the 370–470 nm region peaking around 408 nm owing to the 4f–5d transition of Ce3+ ions, and under 408 nm excitation they showed intense characteristic sharp green emission around 543 nm corresponding to the 5D4 → 7F0–6 transitions of Tb3+ ions. The energy transfer mechanism from Ce3+ to Tb3+ ions was ascribed to the quadruple–quadruple interaction, and the energy transfer efficiency reached as high as 93.2%. Notably, the composition-optimized CYHA:0.03Ce3+,0.6Tb3+ sample exhibited a high internal quantum efficiency (IQE) of 78.5% and external quantum efficiency (EQE) of 56%, which were much higher than those of the Tb3+ singly-activated CYHA:0.6Tb3+ sample (IQE = 8%, EQE = 2.2%). Finally, a prototype white LED device was made by combining a 400 nm near-UV-emitting LED chip with a phosphor blend of the as-prepared CYHA:0.03Ce3+,0.6Tb3+ green phosphors, commercial BaMgAl10O17:Eu2+ blue phosphors and commercial CaAlSiN3:Eu2+ red phosphors, which emitted bright warm-white light with good CIE chromaticity coordinates of (0.391, 0.356), a low correlated color temperature of 3528 K and a high color rendering index of 92.3 under 120 mA driving current. This work opens up new opportunities for the development of efficient color converters toward near-UV-pumped warm-white LEDs with high color rendering index.
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