Surface crystallized Mn-doped glass-ceramics for tunable luminescence

Monolithic luminescent glass-ceramic is highly desirable for solid-state lighting as it is stable and robust, while in practical light-emitting devices only a thin luminescent layer is used for more efficient excitation and light extraction. In this paper, Mn2+-doped glass and glass-ceramic with the composition of 60SiO(2)-8Na(2)O-20ZnO-12Ga(2)O(3) were fabricated by the conventional melt-quenching technique. We observe that the crystallization of alpha-Zn2SiO4 nanocrystals takes place on the glass surface with controllable thickness after heat treatment. The glass samples show typical red emission peaking at lambda = 620 nm that can be ascribed to the spin-forbidden T-4(1g)(G) -> (6)A(1g)(S) transition of Mn2+ (d(5)) located in the octahedral coordination site of the glass host. After surface crystallization this red emission is retained and a new green emission at 528 nm is observed through the control of the crystallization temperature and duration, thus offering tunable emission characteristics promising for the lighting application. This change in the visible emission is interpreted in terms of the change of coordination state of Mn2+ from octahedral in a glass matrix to tetrahedral in the surface precipitated alpha-Zn2SiO4 crystals.