Europium partitioning, luminescence re-absorption and quantum efficiency in (Sr,Ca) åkermanite–feldspar bi-phasic glass ceramics

Abstract

We report on partitioning of europium in bi-phasic åkermanite–feldspar glass ceramics with broadly tunable photoluminescence. Conditions for precipitating Eu-doped microcrystalline (Sr,Ca)-åkermanite from supercooled liquids of the type MO–B₂O₃–SiO₂–Al₂O₃ (M = Mg, Ca and Sr) were evaluated. Formation of secondary anorthite and slawsonite feldspar is controlled by chemical composition and crystallization kinetics. Eu²⁺ precipitates on Sr²⁺ and, to a lesser extent, on Ca²⁺ sites. Static and dynamic Eu²⁺ luminescence spectroscopy and spatially resolved cathodoluminescence spectroscopy are used to explore the distribution of europium between crystallite species and the residual glass phase. It was found that åkermanite precipitation occurs congruently with respect to Sr and Ca partitioning for liquids with Sr/(Sr + Ca) ≥ 0.4. Due to kinetic selection, the Ca-rich side of the (Ca,Sr)₂MgSi₂O₇ solid solution is favored and less strontium is incorporated into the crystal phase relative to the precursor material for liquids with lower strontium content, meaning that strontium enriches in the residual glass phase. Using a selective etching process, the crystalline feldspar phase was separated from the residual glass and åkermanite phases, respectively. In this way, the spectroscopic contributions of each phase could be distinguished from each other, clarifying the problem of external quantum efficiency of photoluminescence and re-absorption in glass ceramics relative to the spectroscopic properties of pure crystals.