Blue-light-excitable broadband yellow-emitting CaGd2HfSc(AlO4)3:Ce3+ garnet phosphors for white light-emitting diode devices with improved color rendering index

The current commercial white light-emitting diodes (LEDs) are generally based on the combination of blue LED chips and Y3Al5O12:Ce3+ yellow phosphors. However, because of the lack of red component, such white LED devices exhibit cool white-light emissions with low color rendering index (Ra < 75, R9 < 0). Therefore, it is urgent to discover new blue-light-excitable yellow-emitting phosphors with enhanced red emissions for fabricating high color-quality white LEDs. In the present work, we demonstrate a novel broadband yellow-emitting CaGd2HfScAl3O12:Ce3+ garnet phosphor for blue-light excited white LEDs with improved color rendering index. The as-prepared CaGd2HfScAl3O12:Ce3+ garnet phosphor possesses a cubic structure with Ia (3) over bard space group, and the unit cell parameters of the representative CaGd2HfScAl3O12:2%Ce3+ phosphor are a = b = c = 12.450 angstrom, alpha = beta = gamma = 90 degrees, and V = 1,929.59(4) angstrom(3). Impressively, we find that the CaGd2HfScAl3O12:Ce3+ garnet phosphor shows an intense absorption band in the 300-500 nm wavelength range with a maximum at 452 nm owing to the 4f -> 5d transition of Ce3+ ions. On 452 nm excitation, the optimal CaGd2HfScAl3O12:2%Ce3+ sample exhibits a broad asymmetric yellow emission band in the wavelength range of 470-750 nm with peak at 564 nm and full width at half maximum of 151 nm. The Commission Internationale de l'Eclairage chromaticity coordinates and internal quantum efficiency of the CaGd2HfScAl3O12:2%Ce3+ sample are (0.4485, 0.5157) and 30.4%, respectively. Finally, a white LED device is fabricated by combing a 450 nm blue LED chip with commercial Y3Al5O12:Ce3+ yellow-emitting phosphor, which generates white light with low color rendering index (CRI; Ra = 74.7, R9 = -12.7) and high correlated color temperature (CCT = 6,554 K) under the 60 mA driving current. In sharp contrast, another white LED device, which is made by coating our as-prepared CaGd2HfScAl3O12:2%Ce3+ yellow-emitting phosphors onto the surface of a 450 nm blue LED chip, produces white-light emission with high CRI value (Ra = 84.5, R9 = 26.3) and relatively low CCT of 5,649 K. This work reveals that the newly discovered broadband yellow-emitting CaGd2HfScAl3O12:Ce3+ phosphors can serve as a potential color converter in high-color-quality phosphor-converted white LEDs. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Current commercial white LEDs are typically composed of blue LED chips and yellow phosphors, resulting in cool white-light emissions with low color rendering index due to the lack of red component. There is a need to discover new blue-light-excitable yellow-emitting phosphors with enhanced red emissions for producing high color-quality white LEDs. The novel CaGd2HfScAl3O12:Ce3+ garnet phosphor shows promising potential as a color converter in high-color-quality phosphor-converted white LEDs.