Improvement of the luminescent thermal stability and water resistance of K2SiF6:Mn4+ by surface passivation

Research progress on surface modifications for phosphors used in light-emitting diodes (LEDs)

“…The PL intensity was reduced by about 55% after 7 days. These results indicate that CaS:Eu 2+ phosphor 34 is very unstable when it is exposed to moisture, in contrast to a decreasing intensity for the uncoated phosphor, indicating that the PMMA-silica nanocomposite coating on the phosphors served as a protective layer by retarding the surface-related damage caused by moisture.…”

“…However, their application is seriously hindered by their easy hydrolysis. Qiang et al 34 proposed to use sodium sulfite as a passivator to treat K 2 SiF 6 :Mn 4+ . After passivation, a Mn 4+ -rare K 2 SiF 6 protective layer could be formed in situ on the surface of the phosphor, and led to improved emission intensity, luminescent thermal stability and moisture resistance.…”

“…(a) Photographs of phosphor immersed in deionized water. (b) PL integrated intensities with different soaking times in water 34.…”

A Na2MoO2F4:Mn4+ phosphor with red luminescence peaking at 625 nm and a ZPL/v6 intensity ratio of 243%

“…Red-emitting phosphors, when added in white light-emitting diodes (WLEDs) to supplement the red component in the spectrum, help increase the color rendering index and reduce the correlated color temperature. [1][2][3][4][5][6] Since the commercialization of K 2 SiF 6 :Mn 4+ , Mn 4+ -doped fluoride phosphors have been widely studied for broad excitation in the blue spectral region and narrow red emission. [6][7][8][9] The emission exhibits several linetype narrow peaks, ascribed to the Stokes, anti-Stokes vibrational phonon sidebands and the zero phonon line (ZPL).…”

Advancing Red-Emitting Fluoride Phosphors for Highly Stable White Light-Emitting Diodes: Crystal Reconstruction and Covalence Enhancement Strategy

“…One significant challenge for ionic fluoride crystals containing [MnF 6 ] 2– is their high propensity to react with water, forming brown-black oxygen-containing compounds that drastically reduce luminescence efficiency. This limitation severely restricts their broad implementation in WLED devices. − Current strategies to address moisture resistance primarily focus on surface-based techniques, such as outer coating, − surface passivation, , and constructing a shell with minimal or no Mn 4+ presence to effectively isolate [MnF 6 ] 2– from water molecules. , Recently, our group developed a novel reduction-assisted surface recrystallization method, enabling the reconstruction of a Mn 4+ -free K 2 SiF 6 inert shell on K 2 SiF 6 :Mn 4+ crystals . The resulting core–shell structure exhibited exceptional stability, maintaining a QE of 97% even after boiling in water for 20 min.…”