A research group led by Prof. ZHANG Jiahua from Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences proposed a Be2+-doping strategy to increase the quantum efficiency of red phosphor CaAl12O19:Mn4+. The work was published in Advanced Optical Materials.

Phosphor-converted light emitting diodes (Pc-LEDs) have shown great benefits in high color gamut display that needs narrow-emitting phosphors. The commercial red narrow-emitting phosphor K2SiF6: Mn4+ has received lots of attentions due to its high efficiency. However, it is prone to deliquescence.

Therefore, it is important to prepare chemical stable and efficient narrow-emitting-red phosphors. CaAl₁₂O₁₉: Mn⁴⁺ (CAO: Mn⁴⁺) is a promising material. However, the quantum efficiency needs to be improved.

This work found that the self-reduction of Mn⁴⁺ to Mn²⁺ is the key reason for the inefficiency of CaAl₁₂O₁₉:Mn⁴⁺. Upon doping of Be²⁺ the self-reduction can be significantly suppressed. The internal quantum efficiency of 74.9% and external quantum efficiency of 56.3% are achieved under UV excitation. In addition, it is found that the luminescence enhancement is inversely proportional to the radius of co-doping metal divalent ions.

By adding CaAl₁₂O₁₉:Mn⁴⁺, Be²⁺ into the backlight source, the LCD display prepared in this work achieved a wide color gamut of 110.1% of NTSC.

This study not only provides a new candidate material for wide color gamut display, but also reveals an important reason for inefficiency in Mn⁴⁺ doped materials and provides charge compensation solution.