This letter reports blue oxynitride phosphors of La1-xCexAl(Si6-zAlz)(N10-zOz) (z∼1) (termed JEM crystal phase) and their application for the white light-emitting diodes (LEDs). The JEM phosphor can be excited by 405 nm light efficiently, and its spectrum can be tuned widely by changing the Ce concentration. The emission spectrum of this phosphor is as wide as 110 nm in full width at half maximum, which is convenient to solid state lighting. The preparation of white LED was attempted by using a 405 nm InGaN chip and oxynitride phosphors in this work. High color rendering index ≫95 was achieved in white LED with various correlated color temperatures, indicating the suitability of the JEM phosphor in solid-state lightings.