Near-infrared emission of Eu2+ in M4Li(BN2)3 (M = Ca, Sr, Ba)

Eu 2+ -doped phosphors show broadband absorption, tunable emission and high quantum efficiency due to the parity-allowed 5d→4f transitions, allowing them to be used in solid-state lighting. To expand their applications in other fields such as detection and sensing technologies, the Eu 2+ emission needs to be tuned into the near-infrared region, but it is a big challenge to obtain Eu 2+ near-infrared region emitters due to the absence of host compounds with extremely large crystal-field splitting. In this work, we chose M 4 Li(BN 2 ) 3 (M = Ca, Sr, Ba) as a host and realize the near-infrared region emission of Eu 2+ in it. Among these phosphors, Ba 4 Li(BN 2 ) 3 :Eu 2+ exhibits the longest emission of 880 nm and the largest full-width at half maximum of 276 nm under 450 nm excitation, while Ca 4 Li(BN 2 ) 3 :Eu 2+ and Sr 4 Li(BN 2 ) 3 :Eu 2+ emit at 740 and 680 nm, respectively. We observe an interesting phenomenon that the energy shift of emission is linearly related to the radius difference between the alkaline earth cation and the activator Eu 2+ in this system.