Mutual energy transfer luminescent properties in novel CsGd(MoO4)2:Yb3+,Er3+/Ho3+ phosphors for solid-state lighting and solar cells

In this work, we prepared a novel kind of Yb3+, Er3+/Ho3+ co-doped CsGd(MoO4)(2) phosphors with a different structure from the reported ALn(MoO4)(2) (A = Li, Na or K; Ln = La, Gd or Y) compounds using a high-temperature solid-state reaction method. X-ray diffraction showed that the as-prepared samples had a pure phase. Based on the efficient energy transfer from Yb3+ to Er3+/Ho3+, the up-conversion (UC) luminescence of the optimal CsGd(MoO4)(2): 0.30Yb(3+), 0.02Er(3+) sample showed intensely green light with dominant emission peaks at 528 and 550 nm corresponding to Er3+ transitions H-2(11/2)-I-4(15/2) and S-4(3/2)-> I-4(15/2), respectively, as well as a weak emission peak originating from F-4(9/2)-I-4(15/2) at 671 nm, under 975 nm laser excitation. The CsGd(MoO4)(2): Yb3+, Ho3+ samples mainly displayed two emission bands around 540 and 660 nm together with a negligible one at 755 nm, which corresponded to Ho3+ transitions F-4(4),F-5(2)-> I-5(8), F-5(5)-> I-5(8) and F-4(4),F-5(2)-> I-5(7), respectively, under 975 nm laser excitation. With increasing Yb3+ concentration in CsGd(MoO4)(2): Yb3+, Ho3+ phosphors, the emission color could be tuned from orange red to light yellow due to the large energy gap between levels F-4(4),F-5(2) and F-5(5). In addition, the CsGd(MoO4)(2): Yb3+, Er3+ showed green light under 376 nm UV irradiation similar to that upon 975 nm laser excitation. However, the emissions for CsGd(MoO4)(2): Yb3+, Ho3+ samples under 358 nm UV or 449 nm blue excitation showed dominant emission peaks at 540 nm and weak 660 nm and 752 nm peaks, which were a bit different from those under 975 nm excitation. Interestingly, we observed efficient energy transfer phenomena (possible quantum cutting) from Er3+/Ho3+ to Yb3+ and a Yb3+-O2- charge transfer (CT) transition in the molybdates, which was deduced from the visible and near-infrared emission spectra and the decrease of the Er3+/Ho3+ luminescent lifetimes with increasing Yb3+ concentration in the CsGd(MoO (4))(2): Yb3+, Er3+/Ho3+ samples. The luminescence properties of these phosphors suggest their potential possibility for applications in solid-state lighting and displays as well as in c-Si solar energy conversion systems

Low-temperature solid-state synthesis and upconversion luminescence properties in (Na/Li)Bi(MoO4)2:Yb3+,Er3+ and Color Tuning in (Na/Li)Bi(MoO4)2:Yb3+,Ho3+,Ce3+ phosphors

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)Bi(MoO4)(2):Yb3+,Er3+ [(N/L)BMO:Yb3+,Er3+] and (Na/Li)Bi(MoO4)(2):Yb3+,Ho3+,Ce3+ [(N/L)BMO:Yb3+,Ho3+,Ce3+] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb3+,Er3+ codoped (N/L)BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er3+, H-2(11/2) -> I-4(15/2)) and 551 nm (Er3+, S-4(3/2) -> I-4(15/2)), in addition to a very weak one at 655 nm (Er3+, F-4(9/2) -> I-4(15/2)). The (N/L)BMO:Yb3+,Ho3+ mainly showed a green band around 544 nm (S-5(2),F-5(4) -> I-5(8)) and a red band around 654 nm (F-5(5) -> I-5(8)) upon 975 nm laser excitation. With increasing Yb3+ concentrations in (N/L)BMO:Yb3+,0.01Ho(3+), the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb3+,Er3+ and Yb3+,Ho3+ were determined to be two-phonons absorption processes in (N/L)BMO:Yb3+,Er3+/Ho3+. The Ce3+ ions were introduced into Yb3+,Ho3+ codoped (N/L)BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho3+ (F-5(4), S-5(2)) + Ce3+ (F-2(5/2)) -> Ho3+ (F-5(5)) + Ce3+ (F-2(7/2)) and (CR2) Ho3+(I-5(6)) + Ce3+ (F-2(5/2)) -> Ho3+ (I-5(7)) + Ce3+ (F-2(7/2)), which is based on the energy matching of Ce3+2F7/2-F-2(5/2) level pairs with Ho3+5I6-I-5(7) and F-5(4),S-5(2)-F-5(5) level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)BMO:Yb3+, Er3+ and (N/L)BMO:Yb3+, Ho3+, Ce3+ materials, and color modulation is easily controlled by varying Yb3+ concentration and a cross relaxation process between Ce3+ and Ho3+, which provides efficient methods to regulate the emission color of UCL phosphors

Mediating exchange bias by Verwey transition in CoO/Fe3O4 thin film

We report the tunability of the exchange bias effect by the first-order metal-insulator transition (known as the Verwey transition) of Fe3O4 in CoO (5 nm)/Fe3O4 (40 nm)/MgO (001) thin film. In the vicinity of the Verwey transition, the exchange bias field is substantially enhanced because of a sharp increase in magnetocrystalline anisotropy constant from high-temperature cubic to lowtemperature monoclinic structure. Moreover, with respect to the Fe3O4 (40 nm)/MgO (001) thin film, the coercivity field of the CoO (5 nm)/Fe3O4 (40 nm)/MgO (001) bilayer is greatly increased for all the temperature range, which would be due to the coupling between Co spins and Fe spins across the interface

Position-Dependent Performance in 5 nm Vertically Stacked Lateral Si Nanowires Transistors

In this work, we investigated the performance of vertically stacked lateral nanowires transistors (NWTs) considering the effects of series resistance. Also, we consider the vertical positions of the lateral nanowires in the stack and diameter variation of the lateral NWTs as new sources of process variability

Stacked optical antennas for plasmon propagation in a 5 nm-confined cavity

The sub-wavelength concentration and propagation of electromagnetic energy are two complementary aspects of plasmonics that are not necessarily co-present in a single nanosystem. Here we exploit the strong nanofocusing properties of stacked optical antennas in order to highly concentrate the electromagnetic energy into a 5 nm metal-insulator-metal (MIM) cavity and convert free radiation into guided modes. The proposed nano-architecture combines the concentration properties of optical nanoantennas with the propagation capability of MIM systems, paving the way to highly miniaturized on-chip plasmonic waveguiding

Quantum entanglement distribution with 810 nm photons through telecom fibers

We demonstrate the distribution of polarization entangled photons of wavelength 810 nm through standard telecom fibers. This technique allows quantum communication protocols to be performed over established fiber infrastructure, and makes use of the smaller and better performing setups available around 800 nm, as compared to those which use telecom wavelengths around 1550 nm. We examine the excitation and subsequent quenching of higher-order spatial modes in telecom fibers up to 6 km in length, and perform a distribution of high quality entanglement (visibility 95.6%). Finally, we demonstrate quantum key distribution using entangled 810 nm photons over a 4.4 km long installed telecom fiber link.Comment: 5 pages, 5 figures, 1 tabl

Optogalvanic Spectroscopy of Metastable States in Yb^{+}

The metastable ^{2}F_{7/2} and ^{2}D_{3/2} states of Yb^{+} are of interest for applications in metrology and quantum information and also act as dark states in laser cooling. These metastable states are commonly repumped to the ground state via the 638.6 nm ^{2}F_{7/2} -- ^{1}D[5/2]_{5/2} and 935.2 nm ^{2}D_{3/2} -- ^{3}D[3/2]_{1/2} transitions. We have performed optogalvanic spectroscopy of these transitions in Yb^{+} ions generated in a discharge. We measure the pressure broadening coefficient for the 638.6 nm transition to be 70 \pm 10 MHz mbar^{-1}. We place an upper bound of 375 MHz/nucleon on the 638.6 nm isotope splitting and show that our observations are consistent with theory for the hyperfine splitting. Our measurements of the 935.2 nm transition extend those made by Sugiyama et al, showing well-resolved isotope and hyperfine splitting. We obtain high signal to noise, sufficient for laser stabilisation applications.Comment: 8 pages, 5 figure