Self‐reduction and enhanced luminescence in transparent Mn²⁺‐doped mullite glass‐ceramics derived from EMT‐type zeolite

Abstract

Mn2+ activated glass‐ceramic (GC) has received tremendous attention in the exploration of luminescent materials for solid‐state lighting due to the high stability, broad red emission, and low toxicity. However, the doped Mn2+ ions still suffer from the oxidation and uncontrollable ions migration during the melting process of conventional preparation techniques, which is detrimental to the luminescence performance. Herein, transparent Mn2+‐doped mullite GCs have been prepared at low temperature (∼850°C) via the spark plasma sintering of EMT‐type zeolite. The GC samples show typical red emission peaking at 620 nm that can be assigned to spin‐forbidden 4T1(G)→6A1(S) transition of Mn2+ located in the octahedral coordination site of the host. Owing to the charge compensation mechanism and produced oxygen vacancies, the self‐reduction of Mn3+ to Mn2+ ions is realized and the oxidization is inhibited. The mullite nanocrystals acted as additional scattering centers introduce Rayleigh scattering to enhance the emission intensity. Moreover, benefitted from the established mullite nanocrystals network, the Mn2+‐doped GCs exhibit improved thermal conductivity up to 1.79 W K−1 m−1 and more excellent mechanical properties than conventional GCs, simultaneously.

Structural and optical properties of Mg1−xMnxP2O6(x = 0–1.0) magnesium metaphosphate

“…The profiles of the spectra are very similar to each other. The main vibration signals are well identified according to the fundamental vibrating units, namely, P 4 O 12 4− ring anion in the phosphate framework reported in Refs. [19][20][21].There are several strong bands at 1300 cm −1 (v as PO 2 ), 1100 and 1010 cm −1 (v s PO 2 ), and 920-1000 cm −1 (v as P-O-P).…”

“…It has been found that most metaphosphate compounds have PO 4 tetrahedral linked together in infinite chains. In MgP 2 O 6 , four PO 4 tetrahedra are connected together in a ring to construct P 4 O 12 4− groups. Only a few metaphosphates with such kind of atom arrangement have been reported.…”

“…Among the transition metal ions, Mn 2+ is one of the most exciting activators used in luminescence materials. Mn 2+ ion has an outer 3d 5 electron configuration, which shows the spin-forbidden 4 T 1 → 6 A 1 transitions in 3d shell. [1][2][3] When Mn 2+ is doped in an octahedral site, it can efficiently give red luminescence ( 4 T 1 → 6 A 1 ) under excitation of near ultraviolet or blue wavelength.…”

“…The luminescence and application of Mn 2+ -activated luminescence material has been one of the research hot spots. [4][5][6] It has been found that phosphates possess rich structure types with high physical and chemical stabilities to ensure practical developments of Mn 2+ -activated phosphors in the fields of lighting and display. Among the kinds of phosphates, the polyphosphates containing the (P 4 O 12 ) 4− ring have been paid more attention in white light emitting diodes, plasma displays, optoelectronic devices, and biochemical probes, and so on.…”

“…Nord et al 16 and Weil 17 have reported the crystal of cyclotetraphosphate MP 2 O 6 (M = Mg, Mn, Fe, Co, Ni, and Cu). The framework is a three-dimensional structure, which is constructed by P 4 O 12 4− cyclotetraphosphate anions groups connected via MO 8 polyhedra, and there are intersecting oxygen tunnels in it. The arrangement of atoms in a lattice can be seen as a series of layers extending along the [0 1 0] direction.…”