Fluorescence and water stability enhancement of K2NaScF6:Mn4+ red phosphor by crystal field optimization of Mg2+/Zn2+ for warm WLEDs

Abstract

Mn 4+ -doped fluoride red phosphors with short fluorescence lifetime can effectively improve the light quality of white light emitting devices (WLEDs), but the poor water stability and low fluorescence intensity restrain their further applications. Therefore, in this work, an effective crystal field optimization strategy (Mn 4+ + Mg 2+ /Zn 2+ → Sc 3+ + Sc 3+ ) is proposed to improve the water stability and fluorescence properties of K 2 NaScF 6 :Mn 4+ red phosphor. Moreover, the experimental investigations demonstrate that the doping of Zn 2+ is the most effective way for optimizing the performance of the phosphor. Here, the luminescence intensity and water stability are enhanced by 77 % and 10 %, respectively, and the fluorescence lifetime is reduced to 2.73 ms. In addition, the structure, morphology, composition, and optical properties of the K 2 NaScF 6 :Mn 4+ ,Zn 2+ phosphor are characterized in detail. Under the effective excitation of blue light, red light exhibits excellent optical properties with low correlated color temperature and high color purity. The optimal doping concentrations of Zn 2+ and Mn 4+ , along with the mechanism of concentration quenching, are determined by theoretical calculations. The crystal field strength ( D q ), the Racah parameters ( B and C ) and the nephelauxetic ratio parameter ( β 1 ) are calculated to evaluate the crystal field environment of K 2 NaScF 6 :Mn 4+ ,Zn 2+ crystal. At a temperature of 423 K, the photoluminescence intensity can be maintained at 45 % of the initial intensity at a temperature of 298 K. Additionally, the excitation energy, chromaticity shift and chromaticity variation are systematically computed. It is worth mentioning that a high-performance warm WLED with a low correlated color temperature (CCT) of 3382 K, high color rendering index (CRI) of 92.3 and luminous efficiency (LE) of 53 lm/W is successfully packaged by using K 2 NaScF 6 :Mn 4+ ,Zn 2+ phosphor as the red component. Furthermore, it exhibits stable output efficiency at high driving current. Therefore, this research offers valuable information to investigate novel and more efficient red-emitting fluoride phosphors for the application in warm WLEDs. • Crystal field optimization improves the water stability and fluorescence intensity. • K 2 NaScF 6 :Mn 4+ ,Zn 2+ phosphor has excellent optical properties. • K 2 NaScF 6 :Mn 4+ ,Zn 2+ phosphor has excellent water resistance and thermal stability. • Using K 2 NaScF 6 :Mn 4+ ,Zn 2+ phosphor, a high-performance warm WLED was obtained.