Defect‐Induced Self‐Reduction and Anti‐Thermal Quenching in NaZn(PO₃)₃:Mn²⁺ Red Phosphor

Abstract

Self‐reduction behavior of doped activators and zero‐thermal‐quenching luminescence have received much more attention in the exploration of luminescent materials for phosphor‐converted white light‐emitting diodes. Here, a combination of the two properties is demonstrated in a Mn2+ activated red phosphor, NaZn(PO3)3:Mn2+, synthesized by a high temperature solid state reaction in ambient atmosphere, which is free from thermal quenching until 250 °C. By combined first‐principles calculation and experimental investigation, the self‐reduction mechanism from Mn4+ to Mn2+ and the anti‐thermal quenching are clarified. The unique properties originate from the cation vacancy defects and the thermally induced energy transfer from the defect energy levels to the Mn2+ 3d excited state centers. This result will deepen the understanding of the effect of the crystal defect on luminescent materials, as well as inspiring more exploration on defect control to develop novel high thermal stability phosphors for practical application.

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

“…However, it was not fully complete, regardless of the Mn-sources. This self-reduction process has also been found in other Mn 2+ -phosphors such as NaZn(PO 3 ) 3 :Mn 2+ , 22 KZn(PO 3 ) 3 :Mn 2+ (ref. 39) and Zn 4 B 6 O 13 :Mn 2+ .…”

“…As a case series, polyphosphates AB(PO 3 ) 3 (A = alkali metals, B = alkali-earth metals and Zn), with several different structure types, tend to form a single-Mn 2+ -doped phosphor even under high temperature calcination in the open air, including NaZn(PO 3 ) 3 :Mn 2+ (ref. 22) and KCa(PO 3 ) 3 :Mn 2+ . 23 Wu et al studied the reason of the self-reduction mechanism for NaZn(PO 3 ) 3 :Mn 2+ by the combination of theoretical calculations, and found that the Zn 2+ vacancy defects and energy transfer from the defect to Mn 2+ responded to this process.…”

Broad luminescence tuning in Mn2+-doped Rb2Zn3(P2O7)2via doping level control based on multiple synergies

“…And then the two negative charges will transfer to the Mn 4+ position to reduce it to Mn 2+ . 27 As for the KMnO 4 doped phosphor, KMnO 4 would decompose into MnO 2 first and then go through the above means to achieve self-reduction to Mn 2+ . The PL decay curves of the RZPO:MnCO 3 (air, Ar/H 2 ), RZPO:MnO 2 (air, Ar/H 2 ), and RZPO:KMnO 4 (air, Ar/H 2 ) samples are shown in Fig.…”

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.…”