Stabilizing Fluoride Phosphors: Surface Modification by Atomic Layer Deposition

Abstract

The use of an Al 2 O 3 -or TiO 2 -coated layer, deposited by using atomic layer deposition (ALD), was explored to improve the adhesion properties of fluoride phosphor particles. K 2 SiF 6 :Mn 4+ was investigated as a benchmark fluoride phosphor. Mn 4+ -doped fluoride phosphors show a narrow red emission band centered at around 630 nm, making them suitable candidates for the red component in white light-emitting diodes. In lighting applications, red fluoride phosphors can lower the correlated color temperature without sacrificing the luminous efficacy of the radiation. In displays, their saturated red emission enlarges the color gamut. Although attractive optical properties are provided by fluoride phosphors, a remaining hurdle is their sensitivity to moisture, which leads to phosphor degradation. Protective hydrophobic shells can be used to enhance the moisture stability of phosphor materials. For fluoride phosphors, the surface fluorine inhibits a good adhesion between the core and shell, potentially leading to delamination of the shell with time. Ideally, the thin ALD-deposited seed layers provide an OH-saturated particle surface, offering an enhanced adhesion to outer moisture barrier layers or hydrophobic encapsulants. The results obtained indicate that the Al 2 O 3 seed layers suffered from delamination and blistering after deposition, related to surface reactions during ALD. In contrast to Al 2 O 3 , the TiO 2 layer could be grown with high uniformity and conformality. In a final step, the ALD-coated fluoride powders were successfully made hydrophobic using a nonchlorinated hydrophobic precursor.

A Secondary Reaction Pathway for the Alumina Atomic Layer Deposition Process with Trimethylaluminum and Water, Revealed by Full-Range, Time-Resolved In Situ Mass Spectrometry

“…Etching side-reactions have been observed in ALD processes before. [32][33][34][35][36] However, the etching of Al during the water pulse in the TMA-water process is a curious phenomenon.…”

A Reverse Strategy to Restore the Moisture‐deteriorated Luminescence Properties and Improve the Humidity Resistance of Mn4+‐doped Fluoride Phosphors

“…Dong et al [27] deposited CaF 2 as a coating material to increase the moisture resistance of K 2 TiF 6 : Mn 4 + phosphor. Smet et al [28] deposited Al 2 O 3 or TiO 2 on the surface of K 2 SiF 6 : Mn 4 + phosphor by means of atomic layer deposition. Peng et al [29] found that a homogeneous K 2 SiF 6 shell on K 2 SiF 6 : Mn 4 + surface can be constructed by ethanol-induced deposition.…”

“…deposited CaF 2 as a coating material to increase the moisture resistance of K 2 TiF 6 : Mn 4+ phosphor. Smet et al . deposited Al 2 O 3 or TiO 2 on the surface of K 2 SiF 6 : Mn 4+ phosphor by means of atomic layer deposition.…”

Dual‐Shelled RbLi(Li3SiO4)2:Eu2+@Al2O3@ODTMS Phosphor as a Stable Green Emitter for High‐Power LED Backlights

“…The stability of RLSO:Eu 2+ @Al 2 O 3 @ODTMS after the dual‐layered protection method treatment exhibits significant improvement towards water erosion. The Al 2 O 3 coating layer fabricated via ALD is dense regardless of the irregularly shape of RLSO:Eu 2+ particles . It increases the intrinsic protection of water permeation .…”