Achieving highly thermostable red emission in singly Mn²⁺-doped BaXP₂O₇ (X = Mg/Zn) via self-reduction

Abstract

The non-rare earth doped red phosphors are attracting wide attention for warm-white lighting and indoor plant cultivation applications. The Mn2+-doped phosphors have well spectral tunability and great potential to generate...

Design of highly efficient energy transfer phosphor Sr4Al14O25:Eu2+,Mn4+ with deep-red emission and application potential in plant growth

“…This is related to the self-reduction phenomenon observed in the Mn. 18 The element Eu appears to have a trivalent valence simultaneously, which was not expected. Unfortunately, co-doping and sintering in a reducing atmosphere will cause the valence of Eu and Mn to become divalent.…”

“…The quantum efficiency of Eu 3+ is not very high since the absorption is weak due to the forbidden transition (f-f), and the emission spectrum features sharp lines. Mn 2+ absorbs very little ultraviolet and visible light, such as in the case of NaCaPO 4 :Mn 2+ , 17,18 resulting in low luminous intensity, which is not ideal for plant growth. The emission of Mn 4+ is attributed to the 2 E -4 A 2 transition, which is less affected by the crystal field and has an emission range that matches the absorption spectra of chlorophyll, making it a suitable luminescent center.…”

Tetrahedrally coordinated rigid crystal structure enables partial self-reduction of mixed-valence europium for optical thermometric application

“…The self-reduction of Eu in the CaBPO 5 matrix can be explained by the charge compensation model. 33,65 Two Eu 3+ ions heterovalently doped at two Ca 2+ sites create a charge negative vacancy, V′′ Ca (Kröger–Vink notation), near the Eu 3+ ion to maintain charge neutrality. The negative charges in the V′′ Ca vacancy will thermally transmit to the Eu 3+ ion, thus reducing the Eu 3+ to Eu 2+ as suggested by the following expressions: 42,48,66 …”

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.…”