Cyan-to-yellow color tunable NaAlSiO4:Eu2+ with high quantum efficiency and thermal stability for white light-emitting diodes

Phosphor-converted white light-emitting diodes (white pc-LEDs) require efficient and thermal stable phosphors with broad-band emission to fulfill the requirement of high-quality illumination. In this work, Eu2+-activated nepheline, NaAlSiO4:Eu2+ with tunable emission was synthesized successfully. The emission band can be tuned from cyan to yellow region through changing flux, synthetic temperature, and/or Eu2+ doping content without changing crystal structure. The tunable emission is due to the variation of occupancy of Eu2+ on two different Na crystallographic sites. Results indicate that using H3BO3 as flux, increasing synthetic temperature and Eu2+ content are beneficial to efficient yellow emission of NaAlSiO4:Eu2+. Na0.92AlSiO4:0.04Eu2+ synthesized at 1300 °C with H3BO3 has high internal (95.14%) and external (78.14%) quantum efficiencies. It also exhibits excellent thermal stability that the emission intensity keeps nearly unchanged within 100 °C. The fabricated proto type white pc-LED by using the phosphor as a yellow component has a color rendering index of 92.0. These results indicate that the as-synthesized phosphors have great potential for application in white pc-LED devices.