Tunable color temperature of Ce3+/Eu2+, 3+ co-doped low silica aluminosilicate glasses for white lighting.

In this paper we report results of tunable lighting in Ce(3+)/Eu(2+,3+) doped low silica calcium aluminosilicate glass. Optical spectroscopy experiments indicate that there is a red color compensation from Eu(2+) and Eu(3+) to the green emission from Ce(3+), resulting in a broad and tunable emission spectra depending on the excitation wavelength. This result analysed in the CIE 1976 color diagram shows a close distance from the Plank emission and a correlated color temperature, varying from 5200 to 3500K. This indicates that our system can be easily excited by GaN based blue LEDs, being an interesting phosphor for white lighting devices.

High values of gain cross section and luminescence quantum efficiency in OH(-)-free Ti3+-doped low-silica calcium aluminosilicate glass.

We recently reported that Ti(3+)-doped low-silica calcium aluminosilicate glass presents long luminescence lifetime (170 micros) and broad emission band (190 nm) shifted toward the visible region when compared with those from Ti(3+):sapphire single crystal and Ti(3+)-doped glasses [Phys. Rev. Lett.100, 027402 (2008)]. Here we demonstrate that this glass also shows high values of both gain cross section (approximately 4.7 x 10(-19) cm(2)) and luminescence quantum efficiency (approximately 70%). By comparing these values with those for Ti(3+):sapphire crystal, we can conclude that the studied Ti(3+)-doped glass is a promising system for tunable solid-state lasers.

Broad emission band of Yb3+ in the nonlinear Nb:RbTiOPO4 crystal: origin and applications.

By means of micro-structural and optical characterization of the Yb:Nb:RbTiOPO(4) crystal, we demonstrated that the broad emission band of Yb(3+) in these crystals is due to the large splitting of the ytterbium ground state only, and not to a complex multisite occupation by the ytterbium ions in the crystals. We used this broad emission band to demonstrate wide laser tuning range and generation of femtosecond laser pulses. Passive mode-locked laser operation has been realized by using a semiconductor saturable absorber mirror, generating ultra short laser pulses of 155 fs, which were very stable in time, under Ti:sapphire laser pumping at 1053 nm.

Spectroscopy of gadolinium gallium garnet crystals doped with Yb(3+) revisited.

The optical spectroscopy measurements of gadolinium gallium garnet (GGG) crystals doped with Yb show evidence of the presence of non-equivalent optical centers with very similar radiative decay rates. The energy level schemes of those centers have been determined on the basis of optical absorption, luminescence and Raman experiments. Crystal field fitting resulted in two sets of slightly different crystal field parameters for two non-equivalent Yb centers. Both sets of parameters describe perfectly the experimentally detected Yb(3+) energy levels. Correlation between systematic trends in the experimental energy level schemes and crystal field parameters is discussed.

Long fluorescence lifetime of Ti3+-doped low silica calcium aluminosilicate glass.

This Letter reports the formation of Ti3+ in OH- free aluminosilicate glass melted under vacuum condition, with a very long lifetime (170 micros) and broad emission band shifted towards the visible region. This lifetime value was attributed to the trapping of the excited electrons by the glass defects and detrapping by thermal energy, and it is 2 orders of magnitude higher than those published for Ti3+ doped materials. Our results suggest that this glass is a promising system to overcome the challenge of extending the spectral range of traditional tunable solid state lasers towards the visible region.

Structural and luminescent properties of new Pb(2+)-doped calcium chlorapatites Ca(10-x)Pb(x)(PO(4))(6) Cl(2) (0≤x≤10).

Excitation and emission spectra of Pb(2+) ions in Ca(10-x)Pb(x)(PO(4))(6)Cl(2) (0≤x≤10) compounds are investigated for various activator concentrations at different temperatures. A calcium-lead chlorapatite system shows a common apatitic structure and occurs as a continuous solid solution. An attempt to identify the pure electronic transitions between the ground and the excited levels of Pb(2+) is made. As a consequence of the two different sites in the apatite, two emission bands due to the [Formula: see text] (at room temperature) and [Formula: see text] (at low temperature) transitions of the Pb(2+) ions are observed. Decay times of Pb(2+) emission have been measured. Experimental data point out thermalization between (3)P(1) and (3)P(0) levels, for example, at very low temperature, the forbidden transition [Formula: see text] is the most intense. The overlap between the emission band of one site and the excitation band of the other site corresponds to an energy transfer phenomenon. Correlations between the luminescence results and the structural data are discussed.

Second-harmonic generation in a microradius LiNbO(3) cylinder with a quasi-elliptical cross section.

LiNbO(3) single-crystal fibers with diameters of 63 and 230 mum were grown, and the second-harmonic-generation (SHG) process was studied with femtosecond laser pulses perpendicularly focused to the fiber. SHG occurred without collinear phase matching, leading to wavelength-independent overall conversion efficiency, unlike in a bulk crystal. The scattering pattern of the second harmonic exhibited an intense forward peak and an almost-uniform, less-intense distribution around the fiber, owing to trapping in high-Q whispering modes. Implementation of a second-order autocorrelator with the 63-mum fiber demonstrates its application potential.