Surface crystallized Mn‐doped glass‐ceramics for tunable luminescence

Abstract

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 60SiO2‐8Na2O–20ZnO–12Ga2O3 were fabricated by the conventional melt‐quenching technique. We observe that the crystallization of α‐Zn2SiO4 nanocrystals takes place on the glass surface with controllable thickness after heat treatment. The glass samples show typical red emission peaking at λ = 620 nm that can be ascribed to the spin‐forbidden 4T1g(G) → 6A1g(S) transition of Mn2+ (d5) 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 α‐Zn2SiO4 crystals.

Crystallization‐induced valence state change of Mn2+ → Mn4+ in LiNaGe4O9 glass‐ceramics

“…As shown in Figure 4B, the glass sample G-0.5 exhibits two absorption bands at 372 nm and 451 nm, which corresponds to the electronic transition 6 A 1g (s) → 4 E 1g (D) and 6 A 1g (S) → 4 A 1g (G), 4 E g (G) of Mn 2+ , respectively, and another band at 351 nm is assigned to the charge transfer absorption. 12,24,25 The absorption spectra changed completely after crystallization, as shown in Figure 4B. Two absorption bands at 413 nm and 331 nm due to the electronic transition 4 A 2g → 4 T 2g and 4 A 2g → 4 T 1g of Mn 4+ are observed, and the absorption bands of Mn 2+ disappear completely.…”

“…As shown in Figure 7A,B, under excitation wavelength (λ = 410 nm), the emission spectra of the sample G-0.5 display a broad band from 500 to 780 nm centering at 613 nm, which can be attributed to spin-forbidden 4 T 1g (G) → 6 A 1g (S) transition of Mn 2+ (d 5 ) located in the octahedral coordination site of the glass host. 12,[34][35][36] In the excitation spectra (monitored at λ = 613 nm), the spectrum shows a strong and broad band located at 265 nm corresponding to Mn-O charge transfer (CT) transition, and three other bands located at 347 nm, 361 nm, and 408 nm, attributed to transitions 6 A 1g (s) → 4 E( 4 D), 6 A 1g (s) → 4 T 2g (D), and 6 A 1g (s) → ( 4 E 1g (G), 4 E 1g (G)), respectively. This result is in good agreement with the absorption spectra ( Figure 4B).…”

“…We then examined the optical properties of the glass and GC samples by absorption and PL spectra. As shown in Figure B, the glass sample G‐0.5 exhibits two absorption bands at 372 nm and 451 nm, which corresponds to the electronic transition 6 A 1g (s) → 4 E 1g (D) and 6 A 1g (S) → 4 A 1g (G), 4 E g (G) of Mn 2+ , respectively, and another band at 351 nm is assigned to the charge transfer absorption . The absorption spectra changed completely after crystallization, as shown in Figure B.…”

“…[9][10][11] Compared with fluoride-based phosphors that are usually accessed by a wet chemistry route and are usually hygroscopic, oxide phosphors are stable and more desirable from viewpoint of application. 12 Oxide hosts with an octahedral site with suitable geometry for Mn 4+ include many germanates and titanates. For instance, Kunitomo et.…”

“…The reddish emission of Mn 4+ can be generated when it is located in an octahedral site in a number of host matrix including fluorides and oxides . Compared with fluoride‐based phosphors that are usually accessed by a wet chemistry route and are usually hygroscopic, oxide phosphors are stable and more desirable from viewpoint of application . Oxide hosts with an octahedral site with suitable geometry for Mn 4+ include many germanates and titanates.…”