Peter Nass

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

We report on partitioning of europium in bi-phasic akermanite–feldspar glass ceramics with broadly tunable photoluminescence. Conditions for precipitating Eu-doped microcrystalline (Sr,Ca)-akermanite 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 akermanite 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 akermanite 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.