Thermal stability and self-reduction of a new red phosphor NaMg(PO₃)₃:Mn²⁺

Abstract

For Mn-activated phosphors, the luminescent performance is strongly dependent on the oxidation state of Mn. In this paper, a series of red phosphors NaMg(PO3)3:xMn2+ (NMP:xMn2+) were synthesized by high temperature...

Cation-defect-induced self-reduction towards efficient mechanoluminescence in Mn2+-activated perovskites

“…Combined with the Bragg rule: 2 d sin θ = λ ( d , θ , λ represents the interplanar spacing, the angle between incident X-ray and corresponding crystal plane, and the wavelength of the X-ray, respectively) and ionic radii (( r (Mg 2+ ) = 0.72 Å, CN = 6), ( r (Ge 4+ ) = 0.39 Å, CN = 4), ( r (Mn 2+ ) = 0.83 Å, CN = 6), ( r (Mn 4+ ) = 0.56 Å, CN = 6), a large radius Mn 2+ ion may occupy a smaller radius Mg 2+ ion, where the Mn 2+ ion is self-reduced from the Mn 4+ ion at high temperature. 27 This point is further proved by Rietveld refinement using GSAS software, where all the samples belong to the orthorhombic Pbca (61) space group. The reliable factors are converged into χ 2 < 3, illustrating that the refined results are trustworthy in Fig.…”

“…Notably, the self-reduction process from Mn 4+ to Mn 2+ ion during sintering under an air atmosphere has been found in silicate, germanate and phosphate systems, because these structures have a rigid tetrahedral unit ([GeO 4 ], [SiO 4 ], [PO 4 ]) that can stabilize the self-reduced Mn 2+ ions. [26][27][28] Interestingly, the self-reduction mechanism is related to defects in the host, and defects play quite an important role in both PersL and ML emission. 29 Hence, inspired by the defect-induced Mn 4+ -Mn 2+ self-reduction process in suitable host crystals, a material with a centrosymmetric perovskite structure is reported to help deeply discuss the ML dynamic process.…”

Achieving excellent thermostable red emission in singly Mn2+-doped near-zero thermal expansion (NZTE) material Li2Zn3(P2O7)2

“…Other bands centered at 347, 365, 412, and 467 nm were noted and ascribed to the spin-forbidden d–d transitions of Mn 2+ from the ground state 6 A 1 ( 6 S) to the excited states, 4 E( 4 D), 4 T 2 ( 4 D), [ 4 A 1 ( 4 G), 4 E( 4 G)], and 4 T 1 ( 4 G), respectively. 43,44 Fig. S3 (ESI†) shows the typical photoluminescence (PL) emission spectra of the LZPO: x Mn 2+ ( x = 0.01–0.5) samples.…”

Self-reduction of Mn4+ to Mn2+: NaY9Si6O26:Mn2+ red phosphors with excellent thermal stability for NUV LEDs

“…Compared to rare earth ions, Mn 4+ , a commonly used red phosphor activator with excellent optical properties and low cost, can be self-reduced in some unique crystal structures in an air environment (Mn 4+ → Mn 2+ ), e.g. , NaMg(PO 3 ) 3 :Mn 2+ , 14 Ba 3 BP 3 O 12 :Mn 2+ , 15 β-KMg(PO 3 ) 3 :Mn 2+ , 16 BaXP 2 O 7 :Mn 2+ (X = Mg/Zn), 17 NaZn(PO 3 ) 3 :Mn 2+ , 18 etc. , exhibiting high thermal stability and anti-quenching phenomena.…”

“…The ideal way to overcome these problems is to keep the low-valent ions stable in the air environment such as in Sr/Ca[B 8 O 11 (OH) 4 ]:Eu; 9,10 CaAl 2 Si 2 O 8 :Eu; 11 a-Ca 3 (PO 4 ) 2 :Eu; 12 M 2 B 5 O 9 Cl:Eu 2+ (M = Sr, Ca) 13 or to use the Eu 3+ -Eu 2+ self-reduction to achieve excellent thermal stability. Compared to rare earth ions, Mn 4+ , a commonly used red phosphor activator with excellent optical properties and low cost, can be self-reduced in some unique crystal structures in an air environment (Mn 4+ -Mn 2+ ), e.g., NaMg(PO 3 ) 3 :Mn 2+ , 14 Ba 3 BP 3 -O 12 :Mn 2+ , 15 b-KMg(PO 3 ) 3 :Mn 2+ , 16 BaXP 2 O 7 :Mn 2+ (X = Mg/Zn), 17 NaZn(PO 3 ) 3 :Mn 2+ , 18 etc., exhibiting high thermal stability and anti-quenching phenomena. Among them, the self-reduction of Mn 4+ results from a reaction between Mn 4+ ions and negatively charged defects: the non-equivalent substitution of Mn 4+ with the host ions creates defects that can provide electrons for selfreduction.…”