Recent Research Progress of Mn4+-Doped A2MF6 (A = Li, Na, K, Cs, or Rb; M = Si, Ti, Ge, or Sn) Red Phosphors Based on a Core–Shell Structure

Abstract

White light emitting diodes (WLEDs) are widely used due to their advantages of high efficiency, low electricity consumption, long service life, quick response time, environmental protection, and so on. The addition of red phosphor is beneficial to further improve the quality of WLEDs. The search for novel red phosphors has focused mainly on Eu2+ ion- and Mn4+ ion-doped compounds. Both of them have emissions in the red region, absorption in blue region, and similar quantum yields. Eu2+-doped phosphors possess a rather broad-band emission with a tail in the deep red spectral range, where the sensitivity of the human eye is significantly reduced, resulting in a decrease in luminous efficacy of WLEDs. Mn4+ ions provide a narrow emission band ~670 nm in oxide hosts, which is still almost unrecognizable to the human eye. Mn4+-doped fluoride phosphors have become one of the research hotspots in recent years due to their excellent fluorescent properties, thermal stability, and low cost. They possess broad absorption in the blue region, and a series of narrow red emission bands at around 630 nm, which are suitable to serve as red emitting components of WLEDs. However, the problem of easy hydrolysis in humid environments limits their application. Recent studies have shown that constructing a core–shell structure can effectively improve the water resistance of Mn4+-doped fluorides. This paper outlines the research progress of Mn4+-doped fluoride A2MF6 (A = Li, Na, K, Cs, or Rb; M = Si, Ti, Ge or Sn), which has been based on the core–shell structure in recent years. From the viewpoint of the core–shell structure, this paper mainly emphasizes the shell layer classification, synthesis methods, luminescent mechanism, the effect on luminescent properties, and water resistance, and it also gives some applications in terms of WLEDs. Moreover, it proposes challenges and developments in the future.

Collaborative Management of Light‐Absorbing Supplementation and Defect Passivation Based on Green‐Emitting ((CH3)4N)2(C2H5)4N·MnBr4 Single Crystals for Efficient and Stable Inverted Perovskite Solar Cells

“…((CH 3 ) 4 N) 2 (C 2 H 5 ) 4 N MnBr 4 ) still has strong optical absorption around 725 nm because the optical leaps of Mn 4+ ions are sensitive to their local coordination; in a symmetric low‐host crystal, Mn 4+ ions can partially break the odd–even forbidden transition rule. [ 36 ]…”

“…((CH 3 ) 4 N) 2 (C 2 H 5 ) 4 N MnBr 4 ) still has strong optical absorption around 725 nm because the optical leaps of Mn 4þ ions are sensitive to their local coordination; in a symmetric low-host crystal, Mn 4þ ions can partially break the odd-even forbidden transition rule. [36] As shown in Figure S4, Supporting Information, the glass/ ITO/PTAA/PMMA/perovskite sample absorbs the majority of light within the wavelength from 300 to 550 nm, but there is still observable light that passes through. Throughout the whole detected wavelength, there is a noticeable increase in its transmittance intensity.…”

Review—The K2SiF6:Mn4+ (PFS/KSF) Phosphor

“…53 The "core-shell" approach of protecting the particle surface against moisture attack has recently been extensively reviewed and we direct the reader to this publication for more information. 54 An alternative approach is to coat the surface with water-resistant coating of a compound that is structurally different from the fluoride compounds. For example, PFS has been coated with SiO 2 , 55 Al 2 O 3 56 and CaF 2 .…”

A theoretical spectroscopy study of the photoluminescence properties of narrow band Eu2+-doped phosphors containing multiple candidate doping centers. Prediction of an unprecedented narrow band red phosphor

“…14,[32][33][34][35][36]38 This is in particular the case with an increasing number of recently synthesized red emitting phosphors, bearing Eu 2,3+ , Ce 3+ and Mn 4+ doping ions in a variety of host structures. [38][39][40] In this concept, successful applications are mainly based on empirical observations and trial and error implying the urgent need for gaining electronic structure knowledge of these kind of systems.…”