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Graphical abstract Near/Mid-IR emission spectra of SGC-1, SGC-3, SGC-0Mn and SGC-10.0Mn glass ceramics samples under 980 nm excitation. Highlights • Near/mid-infrared emission of Er-doped via Mn2+–Yb3+ dimer were investigated. • NIR emission of Er-doped band centered at ∼1.54 µm was increased about four-fold. • MIR emission of Er-doped band centered at ∼2.73 µm was increased about third-fold. Abstract The near/mid-infrared emission of Er3+-doped, Er3+-Yb3+ co-doped and Er3+-Mn2+-Yb3+ tri-doped in 40SiO 2 –(22.9-x)Al 2 O 3 –20BaF 2 –10LaF 3 –5TiO 2 – xMnO–0.1Er 2 O 3 –2Yb 2 O 3 (in mol.%, x = 0, 2.0, 4.0, 6.0 and 10.0) (acronym: SGC-xMn) transparent silicate glass-ceramics were prepared. Enhanced near/mid-infrared emission intensity of Er3+-doped bands centered at ∼1.54 and ∼2.73 µm in transparent silicate glass-ceramics via Mn2+–Yb3+ dimer under 980 nm excitation were investigated. XRD results indicate that the Mn2+ ions are dispersed into the glass matrix. With the forming of Mn2+–Yb3+ dimer and the energy transfer processes from Mn2+–Yb3+ dimer and Mn2+ to Er3+ ions has led to NIR emission intensity of Er3+-doped at ∼1.54 µm was increased significantly about four-fold and the MIR emission intensity of Er3+-doped at ∼2.73 µm was increased about third-fold. In addition, based on the decay time spectra, mechanism of energy transfer processes between Mn2+–Yb3+ dimer, Mn2+ and Er3+ ions were also discussed. [ABSTRACT FROM AUTHOR]

Adaptive filter techniques and the filtered-x least mean square (FxLMS) algorithm have been used in Active Noise Control (ANC) systems. However, their effectiveness may degrade due to the nonlinearities and modeling errors in the system. In this paper, a new feedback ANC system with an adaptive neural controller and variable step-size learning parameters (VSSP) is proposed to improve the performance. A nonlinear adaptive controller with the FxLMS algorithm is first designed to replace the traditional adaptive FIR filter; then, a variable step-size learning method is developed for online updating the controller parameters. The proposed control is implemented without any offline learning phase, while faster convergence and better noise elimination can be achieved. The main contribution is that we show how to analyze the stability of the proposed closed-loop ANC systems, and prove the convergence of the presented adaptations. Moreover, the computational complexities of different methods are compared. Comparative simulation results demonstrate the validity of the proposed methods for attenuating different noise sources transferred via nonlinear paths, and show the improved performance over classical methods. [ABSTRACT FROM AUTHOR]

In this paper, we investigate and report the effects of Si4+/Al3+ (SiO 2 /Al 2 O 3) molar concentration ratio on the self-reduction process of Yb3+ to Yb2+ ions and upconversion (UC)-, visible (VIS)- emission spectra, direct optical bandgaps (DOB), indirect optical bandgaps (IOB) of Bin+/Ybm+, Er3+/Bin+, and Er3+/Bin+/Ybm+ (n, m = 3, 2) co-doped SiO 2 –Al 2 O 3 –MgO–TiO 2 (SAMT) magnesium aluminum silicate glasses. The valence states of the bismuth (Bi), and Ytterbium (Yb) elements in the raw materials mixture existing in the SAMT glass were determined using X-ray photoelectron spectroscopy (XPS) spectra analysis. With the increase of Al3+ molar concentration from 16 mol. % up to 20, 24, 28 and 32 mol. % corresponding to the Si4+/Al3+ (SiO 2 /Al 2 O 3) molar concentration ratio of 3.4, 2.5, 1.9, 1.5, and 1.2, the self-reduction process of Yb3+ to Yb2+ ions was enhanced and thus significantly affected the DOB, IOB, the intensities of UC-, VIS- emission spectra of Bin+/Ybm+, Bin+/Er3+, and Bin+/Er3+/Ybm+ (n = 2, 3) co-doped SAMT glasses under excitation of 473 nm, 808 laser diode (LD) and 980 nm LD. In addition, the CIE 1931(x, y) color coordinates for VIS- and UC- emissions spectra of Bin+/Ybm+, Bin+/Er3+ (n = 2, 3) co-doped SAMT under excitation of 473 nm and 808 nm LD are also calculated and determined in the CIE 1931(x, y) chromaticity diagram. • Effect of Si4+/Al3+ ratio on the self-reduction process of Yb3+ to Yb2+ ions were investigated. • XPS results determined existence of Bi3+, Bi2+, Yb3+, and Yb2+ ions in SiO 2 –Al 2 O 3 –MgO–TiO 2 glass. • CIE1931 for VIS, UC emissions of Bin+/Er3+/Ybm + under excitation of 473, 808 nm were determined. [ABSTRACT FROM AUTHOR]

Graphical abstract Broadband NIR emission spectra of SG-0Er0Nd2Bi, SG-0.4Er0Nd0Bi, SG-0Er0.5Nd0Bi and SG-0.4Er0.5Nd2Bi transparent glass-ceramics samples. Highlights • Broadband NIR emission of Nd–Bi–Er co-doped transparent glass-ceramics was investigated. • A NIR broadband with an FWHM of 600 nm which covered the whole O, E, S, C and L bands was observed. • Mechanism of energy transfer between Bi-related and Er3+, Nd3+ was proposed. • The studied material could provide potential EDFA application in a WDM system. Abstract Super broadband NIR (near-infrared) emission and energy transfer of Nd–Bi–Er co-doped transparent silicate glass-ceramics under excitation 808 nm laser diode were investigated. Super broadband NIR emission in Nd–Bi–Er co-doped extending from 1000 to 1600 nm with a full-width at half-maximum (FWHM) of 600 nm were observed. This result is due to the overlapping NIR emission band centered at 1275 nm (ES 1 → GS) of Bi-related and NIR emission band centered at 1063 nm (4F 3/2 → 4I 11/2) of Nd3+ as well as NIR emission spectral band centered at 1546 nm (4I 13/2 → 4I 15/2) of Er3+. At the same time, the energy transfer processes between Bi-related, Nd3+ and Er3+ were also discussed and proposed. [ABSTRACT FROM AUTHOR]

• Influence of F− on the reduction process of Eu3+ to Eu2+were investigated. • Direct/indirect optical bandgaps of Eu3+/Eu2+–Er3+–Yb3+ co-doped were calculated. • CIE for VIS emissions of Eu3+/Eu2+–Er3+–Yb3+ co-doped was identified. • Energy transfer process between Eu3+/Eu2+ and Er3+ was also discussed. In this paper, we report the influences of F− ions on the reduction process of Eu3+ to Eu2+, and the optical properties of Eu3+/Eu2+–Er3+–Yb3+ co-doped niobate silicate glasses. The visible (VIS), upconversion (UC) emissions, and energy transfer (ET) of Eu3+/Eu2+–Er3+–Yb3+ co-doped niobate silicate glasses under the excitations of 295, 335 nm, and 980 nm laser diode (LD) were investigated. The direct/indirect optical bandgaps and CIE 1931 (x; y) chromaticity coordinates for luminescence of Eu3+/Eu2+–Er3+–Yb3+ co-doped niobate silicate glasses under the excitations of 295, 335 nm were also been calculated and identified. Remarkably, the influences of F− ions and experimental conditions platinum crucibles with the lid on enhancing the reduction process of Eu3+ to Eu2+were also investigated and discussed. [ABSTRACT FROM AUTHOR]