A new cyan phosphor NaAlO2:Bi3+ with high luminescent thermal stability

Developing new phosphors is an important issue for white LED applications. Herein, a simple compound NaAlO2 with an unusual compact 5-coordinated [NaO5] polyhedral environment is selected as host material. After doping Bi3+ into NaAlO2, Bi3+ may be occupy the Na-sites and interesting luminescent properties are expected. Experimental results show that phosphor NaAlO2:Bi3+ can emit cyan light under near-UV excitation. More exciting, the luminescent intensity of NaAlO2 is rather stable under high temperatures, which is due to the good structural rigidity of NaAlO2 host lattice and the process of trap-to-activator energy transfer. At 450 K, the typical working condition of LED devices, the PL intensity constitutes 92 % of the intensity at 300 K, which can guarantee its luminous efficiency for applications in LED devices. Finally, a white LED was fabricated by using a 365 nm LED ship, and a mixture of CaAlSiN3:Eu2+ (red phosphor), BaMgAl10O17:Eu2+ (blue phosphor) and NaAlO2:0.007Bi3+. The CIE coordinates, rendering index (Ra) and Correlated Color Temperature (CCT) of this lamp are (0.3183, 0.3307), 96.8 and 4429 K. This work confirms that the NaAlO2:Bi3+ material is a promising cyan phosphor for applications in LED field.