Confinement effects in sesquioxydes

Two consequences of the small sizes in Eu3+-doped Gd2O3 are observed. First the linewidth of the Eu3+ transitions are inhomogeneously broadened at low temperature, and second the population of the ground and the first excited state of Eu3+ as a function of temperature differs depending on the size: at low temperatures, the smaller the particles, the less populated the first excited state is. The explanation of this second phenomenon could be the absence of very low-energy phonons in small particles.