May 28 | Guna Krieķe

Upconversion luminescence is an anti-Stokes process in which photons with low energy are converted to ones with higher energy. The efficiency of this process is determined by the properties of activator and host matrix. In this research Er³⁺ upconversion luminescence is analysed in oxyfluoride glass ceramics – composites consisting of oxide glass and fluoride nanocrystals.

Novel transparent glass ceramics containing NaREF₄ (RE=La, Gd, Y, Er, Lu) and Ba₄RE₃F₁₇ (RE=Gd, Y, Yb, Lu) has been prepared using melt quenching method. The crystallization and spectroscopic properties have been analysed in glass and glass ceramics.

Main theses:

• In the glass ceramics containing NaLaF₄: Er³⁺, Yb³⁺ increase of Yb³⁺ content promotes the formation of cubic fluorite type NaLaF₄, which currently has been obtained only in oxyfluoride glass ceramics.
• In the crystalline environment of β-NaREF₄: Er³⁺ containing glass ceramics two Er³⁺ positions are associated with incorporation of erbium ions in the rare earth ion positions and the third is related to distortion of these sites caused by half-filled cationic positions.
• In Ba₄RE₃F₁₇: Er³⁺ containing glass ceramics variations in the local environment of Er³⁺ ions are associated with the phase transition from metastable cubic to rhombohedrally-distorted cubic Ba₄RE₃F₁₇.
• In Ba₄Yb₃F₁₇: Er³⁺ containing glass ceramics unusually intense red upconversion luminescence is attributed to three photon energy transfer from Yb³⁺ to Er³⁺, followed by multiphonon relaxation and cross-relaxation between Er³⁺ and Yb³⁺.
• In Ba₄Lu₃F₁₇: Er³⁺ containing glass ceramics the Er³⁺ content in the crystalline phase can be determined by comparing luminescence band intensity ratio and luminescence kinetics of Er³⁺ in glass ceramics and microcrystalline Ba₄Lu₃F₁₇: Er³⁺ with known activator content.