Optical Materials 

Abstract: The physical properties of R2O-ZnO-TeO2 glasses have been studied for their feasibility for fiber drawing and rare earth doping. A tellurite glass fiber with less than 1 dB/m loss has been made by the rod-in-tube method. The spectroscopic properties of rare earth ions (Pr3+, Nd3+, Er3+, and Tm3+) in tellurite glass are discussed and compared with silica, fluoride and chalcogenide glasses.

Abstract: This paper presents an overview of the recent results on upconversion spectroscopy obtained in our group. After a brief introduction into the upconversion field, three different topics will be addressed. First, the near-infrared (NIR) to red/green or blue upconversion efficiencies are discussed for the very efficient upconversion lattice NaYF4 codoped with Er3+, Yb3+/Er3+ or Yb3+/Tm3+, respectively. It will be demonstrated that as much as 50% of the NIR excitation photons contribute to the upconversion emission. Possible application of such a phosphor for enhancing the energy conversion efficiency of solar cells will be discussed. Next, the upconversion spectroscopy of nanocrystalline solutions will be discussed. Most importantly, optically transparent solutions showing intense visible emission under near-infrared excitation, an essential first step for application in new luminescent nanolabels, will be presented. Finally, upconversion spectroscopy of mixed transition metal/rare earth systems will be discussed. Both systems where the sensitizer is the rare earth ion and upconversion occurs on the transition metal ion, and their counterparts (transition metal sensitized upconversion) are presented and their underlying mechanisms will be described. The possibilities for chemical tuning of upconversion properties in such systems are presented.

Abstract: Spontaneous Raman spectra of tungstate (MeWO4) and molybdate (MeMoO4) crystals with sheelite structure were investigated (Me=Ca, Sr, Ba, Pb). The energy shift and line broadening of internal vibrational modes were measured in the temperature range from 77 K to the melting point by means of a high temperature Raman spectroscopic technique. The phase transition from sheelite to cubic structure was discovered at a temperature of 1600 K in a BaMoO4 crystal. Vibrational level diagrams for “free” [WO4]2− and [MoO4]2− tetrahedrons were built on the basis of spontaneous Raman spectra of tungstate and molybdate crystals in the molten state. The effect of mass and electronegativity of Me2+ cations on the position and linewidth of internal vibrational modes was investigated. It was shown that the variation of vibration level diagrams in sheelite series could change the probability of the dephasing and splitting relaxation mechanisms. As a result, the consequent line narrowing of totally symmetric Raman vibrations of [WO4] and [MoO4] tetrahedron complexes was registered in the Raman spectra in a series of sheelite crystals moving from calcium to strontium and barium. Due to the narrowest linewidth (Δν R =1.6 cm −1 ) and the highest peak cross-section of the Raman line in barium tungstate and molybdate crystals, they were proposed as the most efficient sheelite crystals for Raman laser development.

Abstract: Transparent Ce:YAG ceramic phosphors were synthesized from the oxide powder which was produced by co-preparation method of the hydroxides. The Ce:YAG ceramics had a broad emission band peaked at 530 nm due to the 5d → 4f transition of Ce 3+ . The transmittances of the samples obtained were 70–87% at 800 nm. The absorption coefficient and emission intensity of Ce 3+ were increased with increasing thickness. Under 465 nm LED excitation, the color coordinates of the Ce:YAG ceramics shifted from the blue region to yellow region with increasing sample thickness, passing nearby the theoretical white point in the chromaticity diagram. The highest value of luminous efficacy of the ceramic white LED was 73.5 lm/W.