Strong visible up-conversion emission in Tb3+, Tm3+ and Tb3+-Tm3+ co-doped tellurite glasses sensitized by Yb3+

Up-conversion luminescence characteristics under 975 nm excitation have been investigated with Tb3+/Tm3+/Yb3+ triply doped tellurite glasses. Here, green (547 nm: D-5(4) --> F-7(4)) and red (660 nm: D-5(4) --> F-7(2)) up-conversion (UC) luminescence originating from Tb3+ is observed strongly, because of the quadratic dependences of emission intensities on the excitation power. Especially, the UC luminescence was intensified violently with the energy transfer from the Tm3+ ions involves in the Tb3+ excitation. To the Tb3+/Tm3+/Yb3+ triply doped glass system, a novel up-conversion mechanism is proposed as follows: the energy of (3)G(4) level (Tm3+) was transferred to D-5(4) (Tb3+) and the 477-nm UC luminescence of Tm3+ was nearly quenched. (C) 2006 Elsevier B.V. All rights reserved.

Strong visible up-conversion emissions and thermometric applications of Er3+-Yb3+ codoped Al2O3 prepared by the sol-gel method

The Er3+-Yb3+ codoped Al2O3 has been prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)(3)]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)(3) center dot 5H(2)O] and ytterbium nitrate [Yb(NO3)(3) center dot 5H(2)O]. The phase structure, including only two crystalline types of doped Al2O3 phases, theta and gamma, was obtained for the 1 mol% Er3+ and 5 mol% Yb3+ codoped Al2O3 at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300-825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er3+-Yb3+ codoped Al2O3 plays an important role in the application of high temperature sensor.

Infrared-to-visible upconversion emissions in Er3+ doped TeO2-based oxyhalide glasses

The fluorescence and up-conversion spectral properties of Er3+-doped TeO2-ZnO and TeO2-ZnO-PbCl2 glasses suitable for developing optical fiber amplifier and laser have been fabricate and characterized. Strong green (around 527-550 nm) and red (around 661 nm) up-conversion emissions under 977 nm laser diode excitation were investigated, corresponding to H-2(11/2), S-4(3/2), --> I-4(15/2) and F-4(9/2) --> I-4(15/2) transitions of Er3+ ions respectively, have been observed and the involved mechanisms have been explained. The dependence of up-converted fluorescence intensity versus laser power confirm that two-photons contribute to up-conversion of the green-red emissions. The novelty of this kind of optical material has been its ability in resisting devitrification, and its promising optical properties strongly encourage for their further development as the rare-earth doped optical fiber amplifiers and upconversion fiber laser systems.

Energy transfer and infrared-to-visible upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

We report on the energy transfer and frequency upconversion spectroscopic properties of Er3+-doped and Er3+/Yb3+-codoped TeO2-ZnO-Na2O-PbCl2 halide modified tellurite glasses upon excitation with 808 and 978 nm laser diode. Three intense emissions centered at around 529, 546 and 657 nm, alongwith a very weak blue emission at 4 10 nm have clearly been observed for the Er3+/Yb3+-codoped halide modified tellurite glasses upon excitation at 978 nm and the involved mechanisms are explained. The quadratic dependence of fluorescence on excitation laser power confirms the fact that the two-photon contribute to the infrared to green-red upconversion emissions. And the blue upconversion at 410 nm involved a sequential three-photon absorption process. (c) 2005 Elsevier Ltd. All rights reserved.

Infrared-to-visible upconversion flurescence of Er3+/Yb3+-codoped bismuthate glasses

Er3+/Yb3+-codoped bismuthate glasses for developing potential upconversion lasers have been fabricated and characterized. The optimal Yb3+ doping content was investigated in the glasses with different Yb3+-Er3+ concentration ratios and the optimal Yb3+-Er3+ concentration ratio is 5:1. Under 975 nm excitation, intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2), respectively, were observed at room temperature. The quadratic dependence of the 525, 546 and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation. (c) 2004 Elsevier Ltd. All rights reserved.

Infrared-to-visible upconversion fluorescence of Er3+-doped novel lithium-barium-lead-bismuth glass

Er3+-doped lithium-barium-lead-bismuth glass for developing upconversion lasers has been fabricated and characterized. The Judd-Ofelt intensity parameters Omega(t) (t = 2, 4, 6), calculated based on the experimental absorption spectrum and Judd-Ofelt theory, were found to be Omega(2) = 3.05 x 10(-20) cm(2), Omega(4) = 0.95 x 10(-20) cm(2), and Omega(6) = 0.39 x 10(-20) cm(2). Under 975 nm excitation, intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), and F-4(9/2) -> I-4(15/2), respectively, were observed at room temperature. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for the green and red emissions. The long-lived I-4(11/2) level is supposed to serve as the intermediate state responsible for the intense upconversion processes. The intense upconversion luminescence of Er3+-doped lithium-barium-lead-bismuth glass may be a potentially useful material for developing upconversion optical devices. (c) 2004 Elsevier B.V. All rights reserved.

Visible luminescence in Yb3+-doped gadolinium gallium garnets

In this paper, some results on visible luminescence performed on Yb3+-doped gadolinium gallium garnets under 165 and 940 nm excitation were presented. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The gain cross-sections of Yb:GGG crystal as a function of excited-state population fraction P were studied. Emission spectra under 165 nm at 20 K showed there was no charge transfer luminescence in Yb:GGG. (c) 2006 Elsevier B.V. All rights reserved.

Infrared to visible upconversion fluorescence in Yb,Tm : YAG single crystal

Absorption spectrum from 400 to 2000 run and upconversion fluorescence spectra under 940 nm pumping of YAG single crystal codoped with 5 at.% Yb3+ and 4 at.% Tm3+ were studied at room temperature. The blue upconversion emission centered at 483 nm corresponds to the transition (1)G(4) -> H-3(6), the emission band around 646 nm corresponds to the transition (1)G(4) -> F-3(4) of Tm3+. Energy transfer from Yb3+ to Tm3+ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of (1)G(4) level were calculated by using Judd-Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions (1)G(4) -> H-3(6) in YAG doped with Yb3+ and Tm3+ is potentially useful for blue light Output. (c) 2006 Elsevier B.V. All rights reserved.

Strong visible and infrared photoluminescence from Er-implanted silicon nitride films

Silicon nitride films were deposited by plasma-enhanced chemical-vapour deposition. The films were then implanted with erbium ions to a concentration of 8 x 10(20) cm(-3). After high temperature annealing, strong visible and infrared photoluminescence (PL) was observed. The visible PL consists mainly of two peaks located at 660 and 750 nm, which are considered to originate from silicon nanocluster (Si-NCs) and Si-NC/SiNx interface states. Raman spectra and HRTEM measurements have been performed to confirm the existence of Si-NCs. The implanted erbium ions are possibly activated by an energy transfer process, leading to a strong 1.54 mu m PL.

Visible blind p(+)-pi-n(-)-n(+) ultraviolet photodetectors based on 4H-SiC homoepilayers

p(+)-pi-n(-)-n(+) ultraviolet photodetectors based on 4H-SiC homoepilayers have been presented. The growth of the 4H-SiC homoepilayers was carried out in a LPCVD system. The size of the active area of the photodetectors was 300 x 300 mu m(2). The dark and illuminated I-V characteristics had been measured at reverse biases form 0 to 20 V at room temperature, and the illuminated current was at least two orders of magnitude than that of dark current below 13 V bias. The peak value zones of the photoresponse were located at 280-310 nm at different reverse biases, and the peak value located at 300 nm was 100 times greater than the cut-off response value in 380 nm at a bias of 10V, which showed the device had good visible blind performance. A small red-shift about 5 nm on the peak responsivity occurred when reverse bias increased from 5 to 15 V. (c) 2006 Elsevier Ltd. All rights reserved.

Structure and visible luminescence of ZnO nanoparticles

ZnO nanoparticles were synthesized in ethanolic solution using a sol-gel method. The structural and optical properties were investigated by X-ray diffraction, transmission electron microscopy, UV absorption, and photoluminescence. After annealing at 200 degrees C, the particle size is increased and the peak of defect luminescence in the visible region is changed. A yellow emission was observed in the as-prepared sample and a green emission in the annealed sample. The change of the visible emission is related to oxygen defects. Annealing in the absence of oxygen would increase oxygen vacancies. (c) 2006 Elsevier Ltd. All rights reserved.

Strong temperature dependence of photoluminescence properties in visible InAlAs quantum dots

Strong temperature dependence of optical properties has been studied in visible InAlAs/AlGaAs quantum dots, by employing photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. The fast redshift of the exciton emission peak was observed at much lower temperature range compared to that observed in the InAs/GaAs QDs. In TRPL we did not observe the constant decay time even at low temperature. Instead, the observed decay time increases quickly with increasing temperature, showing 2D properties in the transient dynamic process. We attributed our results to the strong lateral coupling effect, which results in the formation of the local minibands or extended states from the discrete energy levels. (C) 2000 Elsevier Science B.V. All rights reserved.

Role of surface defect states in visible luminescence from oxidized hydrogenated amorphous Si hydrogenated amorphous Ge multilayers

Nanocrystalline Ge embedded in amorphous silicon dioxide matrix was fabricated by oxidizing hydrogenated amorphous Si/hydrogenated amorphous Ge (a-Si:H/a-Ge:H) multilayers. The structures before and after oxidation were systematically investigated. The orange-green light emission was observed at room temperature and the luminescence peak was located at 2.2 eV. The size dependence in the photoluminescence peak energy was not observed and the luminescence intensity was increased gradually with oxidation time. The origin for this visible light emission is discussed. In contrast to the simple quantum effect model, the surface defect states of nanocrystalline Ge are believed to play an important role in radiative recombination process. (C) 1999 American Institute of Physics. [S0003-6951(99)02425-0].