Achievement of broadband NIR emission in double perovskite NaLaMgWO6 via non-equivalent substitution of Cr3+

Low-cost and high-efficient broadband near-infrared (NIR) phosphor converted light-emitting diodes (pc-LEDs) are desirable for the compact NIR spectrum system. In this work, a broadband NIR emission with a large full width at half maximum (FWHM) up to ∼160 nm is achieved in double perovskite NaLaMgWO6 phosphor via the non-equivalent substitution of Cr3+. The crystal structure analysis and first-principle calculation have revealed that Cr3+ prefers to substitute Mg2+. In order to keep charge balance, the random-distributed Na+ vacancies are formed. This behavior has constructed two different crystallographic sites for Cr3+ substitution and their effect on the NIR luminescence performances of NaLaMgWO6:Cr3+ is investigated in detail. Within the weak crystal field, the zero phonon line and broadband emissions ascribed to 4T2 → 4A2 transition are present simultaneously, which ensure the large FWHM acquired in NaLaMgWO6:Cr3+. The broadband NIR pc-LED prototype fabricated with the as-prepared phosphor and blue LED chip is achieved, which demonstrates that the NaLaMgWO6:Cr3+ is a new candidate for the broadband NIR phosphor applied in the miniaturized optical devices.