Highly thermal stable phosphor LiSrPO4:Eu2+ with a new crystal structure

ABPO4-type structures are attractive host candidates for phosphors owing to their versatile crystal structures, which makes the great possibility for tuning of luminescent properties. Up till now, there are still some related compounds lack detailed crystal structure informations. And there are also upcoming ABPO4-type structures and related phosphors are under discovering. In this work, Eu2+-activated LiSrPO4 phosphor with a new crystal structure is discovered. Rietveld refinement suggests that it belongs to a monoclinic (m-) system, which exhibits a higher symmetry than the already reported monoclinic one (PDF#53–1238). The Eu2+-activated phosphor exhibits a narrow emission band at 420 nm with a full width at half maximum of 28 nm, which is different from Eu2+ in the old monoclinic or hexagonal (h-) LiSrPO4 with an emission band at around 450 nm. The difference is discussed by comparing the crystal structures especially the coordination environments between the newly found m- and h-LiSrPO4. Eu3+ ion was also used to probe the difference in crystal structure. An additional thermal treatment at 900 °C for the as-prepared samples greatly enhances their emission and quantum efficiency, which is due to the increase of Eu2+/Eu3+ ratio. Integrated emission intensity at 150 °C remains ~94% of the room-temperature value for either one-step or two-step sintering process. Results suggest that the as-prepared phosphor can be a good candidate for phosphor-converted white light-emitting diodes.