Phase Transformation of a K₂GeF₆ Polymorph for Phosphors Driven by a Simple Precipitation-Dissolution Equilibrium and...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photoluminescence

Background:

• Controlling crystal phase transformations is crucial for optimizing phosphor properties.
• Manganese-doped potassium hexafluorogermanate (KGF) is a polymorphic phosphor with unclear phase transformation mechanisms.

Purpose of the Study:

• To investigate the thermodynamic and kinetic mechanisms of KGF phase transformations.
• To achieve stable KGF polymorphs with desirable optical properties and stability.

Main Methods:

• Synergistic use of hydrofluoric acid solution and Si⁴⁺ ions to induce phase transformation.
• In situ monitoring of morphological changes during phase transformation.
• Full structural refinements and electronic band structure calculations.

Main Results:

• Successfully transformed KGF polymorphs to a Si⁴⁺-doped hexagonal phase.
• Identified the most stable phase as Si⁴⁺-doped hexagonal KGF based on energy calculations.
• Demonstrated that phase transformation is driven by precipitation-dissolution equilibrium and ionic exchange.

Conclusions:

• The study elucidates the mechanism of phase transformation in KGF phosphors.
• The Si⁴⁺-doped hexagonal KGF phase exhibits superior stability and photoluminescence.
• This work provides a pathway for designing advanced phosphors through controlled phase engineering.