Highly efficient rare-earth-free deep red emitting phosphor La2Li1−ySb1−xO6:xMn4+,yMg2+: application in high-power warm w-LEDs

Abstract

Phosphor-in-glass (PiG), which serves as both a luminescent convertor and organic encapsulation material in high-power white light-emitting diodes (w-LEDs), has become a prospective research hotspot owing to its high transparency and thermal stability. However, YAG:Ce³⁺ PiG-based LED devices still suffer from a lack of a red component. Therefore, the development of red phosphors with excellent quantum efficiency and superior thermal stability is urgent. Herein, a highly efficient La₂Li_1−ySb_1−xO₆:xMn⁴⁺,yMg²⁺ red phosphor with a broadband emission ranging from 670 to 720 nm was fabricated via a conventional solid-state reaction. By co-doping Mg²⁺ in La₂LiSbO₆:Mn⁴⁺, the emission intensity was enhanced significantly, which reaches as high as 10 times that of the single-doped La₂LiSbO₆:Mn⁴⁺. It is proposed that the Mg²⁺ dopant can compensate imbalanced charges for the substitution of Sb⁵⁺ by Mn⁴⁺ and interrupt adverse energy transfer among the Mn⁴⁺ activators. Impressively, a maximum quantum yield of up to 80.3% is achieved and about 80% emission intensity is retained at the temperature of 423 K. Furthermore, the crystal field strength (D_q) and Racah parameters (B and C) together with the nephelauxetic ratio (β₁) were calculated based on the obtained spectroscopic data. By embedding the red-emitting La₂LiSbO₆:Mn⁴⁺,Mg²⁺ phosphor and yellow-emitting YAG:Ce³⁺ phosphor into TeO₂-based glass, an inorganic PiG composite as a color converter to replace organic silicone was acquired. The excellent optical parameters and tunable chromaticity feature of the fabricated w-LEDs were achieved by adjusting the mass ratio of La₂LiSbO₆:Mn⁴⁺,Mg²⁺ to YAG:Ce³⁺ in the PiG plate, where the correlated color temperature changed from cool white (6555 K) to warm (4130 K) and the color rendering index increased from 73.7 to 86.6 under an operating current of 300 mA.