Ultraviolet and visible up-conversion luminescence of Er3+/Yb3+ co-doped CaF2 nanocrystals in sol–gel derived glass-ceramics

• Published in: Journal of luminescence 2013-11, Vol.143, p.150-156
• Main Authors: Georgescu, S., Voiculescu, A.M., Matei, C., Secu, C.E., Negrea, R.F., Secu, M.
• Format: Article
• Language: English
• Subjects: CaF2; Calcium fluoride; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Diffraction; Emission; Exact sciences and technology; Glass ceramics; Growth from solid phases (including multiphase diffusion and recrystallization); Luminescence; Materials science; Materials synthesis; materials processing; Methods of crystal growth; physics of crystal growth; Nanocrystalline materials; Nanocrystals; Nanoscale materials and structures: fabrication and characterization; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Photoluminescence; Physics; Sol–gel; Up-conversion luminescence; Upconversion; X-rays
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2013.04.002

Glass-ceramics containing Er3+/Yb3+ codoped CaF2 nanocrystals have been prepared by using the controlled crystallization above 650°C of the (Yb3+/Er3+) codoped CaF2–SiO2 xerogels. X-ray diffraction and scanning electron microscopy data have revealed the formation of CaF2 nanocrystals of about 16nm size. For pumping at 973nm, this glass-ceramics shows, besides green and red up-conversion luminescence, violet (at ∼408nm) and near-ultraviolet emission (at ∼380nm). The mechanisms responsible for the upconversion luminescence are presented and discussed. The fluorescence lifetimes of the metastable levels responsible for violet, green and red luminescence are measured and their quantum efficiencies are estimated. •Annealing of the Yb/Er doped SiO2–CaF2 xerogel induces the crystallization of CaF2 nanocrystals.•Rare-earth ions are embedded in the glass and in the CaF2 nanocrystals.•UV and VIS up-conversion luminescence is due to Er3+ ions through multi-photon processes.•Cross relaxation process reduces the efficiency of the UV up-conversion luminescence.•UV up-conversion luminescence depends on the energy phonons of the lattice.