Simple Method to Estimate Fractional Numbers of Eu ³⁺ Ions in Different Phases in Highly Luminescent ZrO ₂ –SiO ₂ Nanocomposites

Luminescent, transparent nanocomposites incorporating very tiny crystals in glassy host matrix are a strategy to control a local structure with low phonon energy and/or adjustable band structure, and the charge‐transfer state of luminescent centers such as rare‐earth ions, resulting in their high photoluminescence (PL) efficiency and controllable absorption–emission route mechanism. For this purpose, it is important to know how many luminescent dopants can be incorporated into the nanocrystal domains. Herein, Eu 3+ ‐doped ZrO 2 –SiO 2 nanocomposites are considered as a test case, together with the starting gel thermal evolution. The progressive sol–gel chemistry enables the preferential introduction of Eu 3+ ions into the ZrO 2 nanocrystals. An analytical method using the Eu 3+ PL decay curves quantitatively reveals for the first time that the number of Eu 3+ ions doped in the ZrO 2 crystalline nanodomains, which is obtained above 900 °C, exceeds 60%, and increases to 76% when the thermal treatment temperature is 1100 °C. The fractional number of Eu 3+ ions and the local asymmetry ratio of Λ = I( 5 D 0 − 7 F 2 )/I( 5 D 0 − 7 F 1 ) for each region are estimated as Λ = 2.1–2.9, Λ ≈ 15, and Λ = 4.6–7.4 for the ZrO 2 , boundary, and SiO 2 ‐rich glass phases, depending on the heat‐treatment temperature.