Ion exchange-assisted surface passivation toward highly stable red-emitting fluoride phosphors for light-emitting diodes.

A facile and environmentally friendly ion exchange-assisted surface passivation (IASP) strategy is presented for synthesizing red emitting Mn4+-activated fluoride phosphors. A substantial, pristine Mn4+-free shell layer, applied as a coating to Mn4+ doped potassium fluorosilicate K2SiF6:Mn4+ (KSFM) phosphors, enhances both water resistance and luminescence efficiency. The stability test of fluoride in water at ambient temperature and boiling water demonstrates that IASP-treated KSFM phosphors are highly water resistant. Furthermore, both the negative thermal temperature (NTQ) fitting results and the photoluminescence (PL) decay confirm that the IASP process effectively passivates surface defects, leading to enhanced luminescence performance. The maximum internal quantum yield (QYi) of the IASP-KSFM phosphor is 94.24%. A white LED realized a high color rendering index (CRI) of 93.09 and luminous efficiency (LE) of 149.48 lm/W. This work presented a novel technique for the development of stable fluoride phosphors and has the potential to increase the use of KSFM phosphors in plant supplementary lighting systems and white light-emitting diodes.

Anomalous Octahedron Distortion of Bi-Alloyed Cs2AgInCl6 Crystal via XRD, Raman, Huang-Rhys Factor, and Photoluminescence.

The refinement of XRD patterns only provides the average structure parameters for the alloying materials because of the symmetric protection. Raman vibrational modes can append the detailed information about the bond length and structure. The refinements of XRD patterns for Bi alloying Cs2AgInCl6 revealed the strong structure distortion with the enlarged octahedron of In(Bi)Cl6 and the contracted octahedron of AgCl6 with the increasing Bi. Raman spectra supported the expanded octahedron of InCl6 and the reduced octahedron of AgCl6 but identified the anomalous shortening bond length of Bi-Cl with the increasing Bi. These distorting octahedrons break parity forbidden transition, modify Huang-Rhys factor, and result in the maximum values at 30% Bi alloying and the same variation trend for both photoluminescence and Huang-Rhys factor with the increasing Bi alloying.