Photoluminescence and structural characteristics of Lu2O3:Eu3+ nanocrystallites in silica matrix

Two silica ceramics were obtained by mixing nanocrystalline Lu2O3:Eu3+ with silica sol using the sol–gel technique. The synthesis procedure for both samples differed in the pH of the sol and time of the sol condensation before substrates were mixed together, which implied their different optical properties. The first one has the same spectroscopic properties as Lu2O3:Eu3+ nanocrystallites with an exception of small lowering of the charge transfer (CT) band intensity. This feature is preserved up to about 950 °C. Above this temperature, nanocrystallites of Lu2O3:Eu3+ react with the silica matrix synthesis pyrosilicate (Lu2Si2O7). The Eu3+ ions occupy only one crystallographic site in the crystal lattice for low concentration of the activator (1%) and two sites for higher concentration (10%). The second sample exhibits different Eu3+ emission than Lu2O3:Eu3+ nanocrystallites and, additionally, a broad band of the matrix originating at the green region of the spectrum. Sintering the sample at higher temperatures leads to disappearance of this broad emission and continuous changes of the Eu3+ emission because of the progressive conversion of the Lu2O3:Eu3+ to pyrosilicate. At 1300 °C for both samples, the reaction of synthesis lutetium pyrosilicate is completed. Structural characteristic of the samples is presented and correlate with the decay profile of the Eu3+ emission.