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A large-scale sub-5 nm nanofabrication technique is developed based on double layer anodized aluminium oxide (AAO) porous membrane masking. This technique also provides a facile route to form multilayer nano-arrays (metal nanoarrays sandwiched by AAO membranes), which is very challenging for other techniques. Normally the AAO mask has to be sacrificed, yet in this work it is preserved as a part of the nanostructure. The preserved AAO layers as the support for the second/third layer of the metal arrays provide a high-refractive index background for the multilayer metal arrays. This background concentrates the local E-field more significantly and results in a much higher Surface-Enhanced Raman Spectroscopy (SERS) signal than single layer metal arrays. This technique may lead to the advent of an inexpensive, reproducible, highly sensitive SERS substrate. Moreover, the physical essence of the plasmonic enhancement is unveiled by finite element method based numerical simulations. Enhancements from the gaps and the multilayer nanostructure agree very well with the experiments. The calculated layer-by-layer electric field distribution determines the contribution from different layers and provides more insights into the 3D textured structure.

Abstract: A series of red-emitting phosphors Eu3+-doped M 2Gd4(MoO4)7 (M=Li, Na) have been successfully synthesized at 850°C by solid state reaction. The excitation spectra of the two phosphors reveal two strong excitation bands at 396nm and 466nm, respectively, which match well with the two popular emissions from near-UV and blue light-emitting diode chips. The intensity of the emission from 5D0 to 7F2 of M 2(Gd1−x Eu x )4(MoO4)7 phosphors with the optimal compositions of x=0.85 for Li or x=0.70 for Na is about five times higher than that of Y2O3:Eu3+. The quantum efficiencies of the entitled phosphors excited under 396nm and 466nm are also investigated and compared with commercial phosphors Sr2Si5N8:Eu2+ and Y3A5O12:Ce3+. The experimental results indicate that the Eu3+-doped M 2Gd4(MoO4)7 (M=Li, Na) phosphors are promising red-emitting phosphors pumped by near-UV and blue light. [Copyright &y& Elsevier]

Abstract: High-quality pure PbF2, Yb:PbF2 and Yb, Na:PbF2 crystals are grown by the Bridgman method in a nonvacuum atmosphere. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes belonging to the transitions between ground state 2F7/2 and the excited state 2F5/2 of Yb3+ ions in these crystals have been investigated. The influence of codoping with Na+ ions on the spectra has been studied. Experimental results show that codoping Na+ ions in different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in a PbF2 lattice in a large scope: the Na+ ions codoping with Yb3+ as charge compensators can suppress the deoxidization of Yb3+ to Yb2+, enhance the luminescence intensity and lengthen luminescence lifetime of Yb3+ ions. [Copyright &y& Elsevier]

We report on the growth, polarized spectroscopy and first laser operation of an orthorhombic (space group Pnma) Tm 3+ ,Ho 3+ -codoped gadolinium orthoscandate (GdScO 3 ) perovskite-type crystal. A single crystal of 3.76 at.% Tm, 0.35 at.% Ho:GdScO 3 was grown by the Czochralski method. Its polarized absorption and fluorescence properties were studied revealing a broadband emission around 2 µm. The parameters of the Tm 3+ ↔ Ho 3+ energy transfer was quantified, P 28  = 1.30 × 10 -22 cm 3 µs -1 , and P 71  = 0.99 × 10 -23 cm 3 µs -1 , and the thermal equilibrium lifetime was measured to be 3.5 ms. The crystal-field splitting of Tm 3+ and Ho 3+ multiplets in Cs symmetry sites of the perovskite structure was determined by low-temperature spectroscopy and the mechanism of spectral line broadening is discussed. The continuous-wave Tm,Ho:GdScO 3 laser generated 1.16 W at ∼2.1 µm with a slope efficiency of 50.5%, a laser threshold of 184 mW, a linear laser polarization (E || c) and a spatially single-mode output. The Tm,Ho:GdScO 3 crystal is promising for broadly tunable and femtosecond mode-locked lasers emitting above 2 µm.

We report on the investigation of continuous-wave (CW) and SEmiconductor Saturable Absorber Mirror (SESAM) mode-locked operation of a Yb:GdScO 3 laser. Using a single-transverse-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:GdScO 3 laser delivers 343 mW output power at 1062 nm in the CW regime, which corresponds to a slope efficiency of 52%. Continuous tuning is possible across a wavelength range of 84 nm (1027-1111 nm). Using a commercial SESAM to initiate mode-locking and stabilize soliton-type pulse shaping, the Yb:GdScO 3 laser produces pulses as short as 42 fs at 1065.9 nm, with an average output power of 40 mW at 66.89 MHz. To the best of our knowledge, this is the first demonstration of passively mode-locking with Yb:GdScO 3 crystal.