A high quantum yield red phosphor NaGdSiO4: Eu3+ with intense emissions from the 5D0→7F1,2 transition

Abstract

Red phosphors with a high quantum yield and a lower thermal quenching are needed to improve the luminescence efficiency and the stability of phosphor-converted white light-emitting diodes (pc-WLEDs). We have designed a high quantum yield NaGdSiO4 (NGSO) based phosphor with enhanced Eu3+ emissions of the 5D0→7F1 and 5D0→7F2 transitions. This design is based on the Eu3+ at both the inversion and non-inversion symmetry sites. In detail, we have studied the structure, morphology, and luminescence properties of NGSO: Eu3+ phosphors. Using a 394 nm UV excitation, a series of Eu3+ emissions of 5D0→7FJ (0–4) transitions has been observed. The internal quantum efficiency (IQE) is 83.42% and the red color purity is 91.4%. These values are much higher than some reported results. The higher IQE and double intense 5D0→7F1 and 5D0→7F2 emissions might originate from an unusual structure disorder around Eu3+ ions in the NGSO lattice. The lifetime of the optimal phosphor NGSO: 0.5Eu3+ is about 2 ms, suitable for solid-state lighting. The intensities of the strong emissions at 595 and 624 nm of NGSO: 0.5Eu3+ at 150 °C is about 85% of that at 30 °C, demonstrating its excellent thermal stability. Furthermore, this red NGSO: 0.5Eu3+ phosphor was packaged into a warm pc-WLED, exhibiting a lower correlated color temperature (CCT) of 4222 K and a comparable color rendering index (CRI) of 86.7. These results show that this red phosphor could act as a red component of pc-WLEDs excited by the n-UV LED chip.