Wojciech M. Jadwisienczak

Visible cathodoluminescence of GaN doped with Dy, Er, and Tm

We reported the observation of visible cathodoluminescence of rare-earth Dy, Er, and Tm implanted in GaN. The implanted samples were given isochronal thermal annealing treatments at a temperature of 1100 °C in N2 or NH3, at atmospheric pressure to recover implantation damages and activated the rare-earth ions. The sharp characteristic emission lines corresponding to Dy3+, Er3+, and Tm3+ intra-4fn-shell transitions are resolved in the spectral range from 380 to 1000 nm, and observed over the temperature range of 8.5–411 K. The cathodoluminescence emission is only weakly temperature dependent. The results indicate that rare-earth-doped GaN epilayers are suitable as a material for visible optoelectronic devices.

Visible cathodoluminescence of Er-doped amorphous AlN thin films

In this report, we demonstrate the observation of visible cathodoluminescence (CL) of Er-doped amorphous AlN films produced by sputtering. Optical transmission studies point out that the films are highly transparent and the band gap is about 5.61 eV. Elemental analysis by Rutherford backscattering spectrometry shows that AlN films are stoichiometric. X-ray diffraction measurements reveal that the films retain the amorphous structure even after annealing in N2 ambient at 1000 °C. The sharp characteristic emission lines in the CL spectra correspond to Er3+ intra-4fn shell transitions and are observed over the temperature range of 9–330 K. The results indicate the suitability of Er-doped amorphous AlN films for light-emitting device applications.

Photoluminescence and cathodoluminescence of GaN doped with Pr

We report on our observation of visible photoluminescence and cathodoluminescence of Pr-implanted GaN. The implanted samples were subjected to isochronal thermal annealing treatments at a temperature of 1100 °C in N 2 at atmospheric pressure to recover from implantation damage and activate the rare earth ions. The sharp characteristic emission lines corresponding to Pr 3+ intra- 4f n -shell transitions are resolved in the spectral range from 400 to 1000 nm and observed over the temperature range from 12 to 335 K. We have developed an energy level diagram for Pr 3+ ions in GaN using recorded spectra. The photoluminescence decay kinetics measurements of 3 P 1 , 3 P 0 , and 1 D 2 levels and quenching mechanism analysis allow us to conclude that the dominant de-excitation process is of electric dipole–electric quadrupole type. We found also that the 1 D 2 level separated from the upper 3 P 0 level by 3755 cm−1 energy gap can be populated in several ways, by direct energy transfer processes, cross relaxation | 3 P 0 , 3 H 4 〉→| 1 D 2 , 3 H 6 〉 and cascade processes from the 3 P 0 or higher levels. The full width at half maximum of the strongest photoluminescence line at 653 nm, the 3 P 0 level, is 2.9 meV at 13 K, with a 1.86 meV blue peak shift in going from 13 to 330 K temperature, while the line at 670 nm, 3 P 1 level, has a full width at half maximum of 4 meV at 13 K and a 1.6 meV red peak shift. The thermal stability of GaN:Pr 3+ epilayers indicates the suitability of this material for visible optoelectronic devices.

Visible emission from AlN doped with Eu and Tb ions

We report the observation of visible cathodoluminescence (CL) from AlN thin films grown on sapphire (0001) substrate by molecular beam epitaxy and doped by implantation with Eu3+ and Tb3+ ions. The strongest rare earth (RE) CL was observed from samples annealed at 1100 °C for 0.5 h in N2 ambient. The sharp characteristic emission lines corresponding to Eu3+ and Tb3+ intra-4fn shell transitions are resolved in the spectral range from 350 to 900 nm. The CL spectra were recorded over 1–16 keV electron energy in the temperature range of 8–330 K. The depth resolved CL spectral analysis gives the luminescence surface a dead layer thickness of ∼16 nm for implanted AlN samples. We observed several different recombination centers luminescing in the 286–480 nm spectral region due to the presence of structural defects and oxygen impurities. The time resolved spectra and the CL kinetics were studied. The decay times for 5D0→7F2 (Eu3+), 5D3→7F5 (Tb3+), and 5D4→7F6 (Tb3+) transitions at 300 K are ∼0.4, ∼0.9, and ∼0.4 m...

Luminescence properties of GaN and Al0.14Ga0.86N/GaN superlattice doped with europium

We report the observation of visible photoluminescence and cathodoluminescence of Eu3+ ions implanted in GaN and Al0.14Ga0.86N/GaN superlattice. The sharp characteristic emission lines corresponding to Eu3+ intra-4f6-shell transitions are resolved and observed over the temperature range of 7–330 K. The luminescence shows dominant transitions 5D0→7F1,2,3 and weaker 5D0→7F4,5,6 and 5D1→7F1. The luminescence emission is very weakly temperature dependent. The intensity of Eu3+ emission from Al0.14Ga0.86N/GaN superlattice annealed in N2 is ∼58% stronger than from Eu3+ in the GaN layer. The Al0.14Ga0.86N/GaN superlattice and GaN epilayers may be suitable as a material for visible optoelectronic devices.

Photoluminescence and cathodoluminescence of GaN doped with Tb

We report the observation of the visible cathodoluminescence and photoluminescence of Tb3+ ions implanted in GaN. The sharp characteristic emission lines corresponding to Tb3+ intra-4f8-shell transitions are resolved in the spectral range from 350 to 900 nm, and observed over the temperature range of 7–330 K. The luminescence shows transitions which originate in the 5D3 and 5D4 levels and terminated in the 7F manifolds. The cathodoluminescence emission is only weakly temperature dependent. The results indicate that Tb-doped GaN epilayers may be suitable as a material for visible optoelectronic devices.

Luminescence of Tb ions implanted into amorphous AlN thin films grown by sputtering

We report the observation of visible cathodoluminescence (CL) of Tb ions implanted into amorphous AlN films produced by sputtering. The implanted samples were subjected to thermal annealing treatment up to 1100 °C to optically activate the incorporated ions. The results show that up to 1000 °C annealing temperature the films remain amorphous and the Tb3+ emission intensity increases. The amorphous AlN:Tb films were characterized by x-ray diffraction, CL, and CL kinetics measurements. The sharp characteristic emission lines corresponding to intra-4fn-shell transitions are resolved in the spectral range from 350 to 750 nm, and observed over the temperature range from 7 to 330 K due to the transitions from 5D3 and 5D4 levels toward the 5FJ (J=2 to 6) multiplets. Finally, CL kinetics measurements have revealed that decay times of 5D3→7FJ and 5D4→7FJ transitions are in the range 0.94–0.77 and 0.49–1.61 ms at 300 K, respectively.

Spectroscopic properties of Sm3+(4f 5) in GaN

We have analyzed the cathodoluminescence spectra of Sm3+ ions implanted and annealed in GaN epilayers. High-resolution emission spectra were obtained at 11 K between 350 and 1050 nm, representing transitions from the 4G5/2 to the 6HJ and 6FJ manifolds of Sm3+(4f5). Emission lifetimes were determined at various temperatures between 7 and 320 K for transitions from 4G5/2 to 6H5/2, 6H7/2, and 6H9/2. Lattice-sum calculations were carried out to determine the crystal-field splitting of the multiplet manifolds. With individual Stark levels and corresponding wave functions identified, the matrix elements for both electric–dipole and magnetic–dipole transitions were calculated between levels. Radiative lifetimes were calculated and compared with experimental lifetimes. High quantum efficiencies are reported. The calculated branching ratios for transitions from 4G5/2 to 6HJ and 6FJ manifolds indicate that transitions to 6H5/2, 6H7/2, and 6H9/2 account for 80% of the total observed emission.

Single-crystal γ-MnS nanowires conformally coated with carbon.

We report for the first time the fabrication of single-crystal metastable manganese sulfide nanowires (γ-MnS NWs) conformally coated with graphitic carbon via chemical vapor deposition technique using a single-step route. Advanced spectroscopy and electron microscopy techniques were applied to elucidate the composition and structure of these NWs at the nanoscale, including Raman, XRD, SEM, HRTEM, EELS, EDS, and SAED. No evidence of α-MnS and β-MnS allotropes was found. The γ-MnS/C NWs have hexagonal cross-section and high aspect ratio (∼1000) on a large scale. The mechanical properties of individual γ-MnS/C NWs were examined via in situ uniaxial compression tests in a TEM-AFM. The results show that γ-MnS/C NWs are brittle with a Youngs modulus of 65 GPa. The growth mechanism proposed suggests that the bottom-up fabrication of γ-MnS/C NWs is governed by vapor-liquid-solid mechanism catalyzed by bimetallic Au-Ni nanoparticles. The electrochemical performance of γ-MnS/C NWs as an anode material in lithium-ion batteries indicates that they outperform the cycling stability of stable micro-sized α-MnS, with an initial capacity of 1036 mAh g(-1) and a reversible capacity exceeding 503 mAh g(-1) after 25 cycles. This research advances the integration of carbon materials and metal sulfide nanostructures, bringing forth new avenues for potential miniaturization strategies to fabricate 1D core/shell heterostructures with intriguing bifunctional properties that can be used as building blocks in nanodevices.

Stability of the Mn photoluminescence in bifunctional ZnS:0.05Mn nanoparticles

We investigate the stability of the orange band photoluminescence (PL) of bifunctional nanoparticles of Mn2+-doped ZnS at 5% (ZnS:0.05Mn). These 4-nm nanoparticles are synthesized via a one-step inorganic chemical route under ambient conditions. The phase, crystallinity, and morphology are analyzed via X-ray and electron diffractions and high-resolution electron microscopy. Based on the thermally activated carrier-transfer model, it is found that orange emission is rather stable at low temperatures and possesses thermal activation energy of ∼18 meV. The analysis of the PL decay curves suggests the coexistence of multiple lifetimes, that the shortening observed in PL lifetime is not due to the Mn2+ ions, and that the orange band decay is stable in temperature range from 10 K to 300 K. The measured M-H hysteresis loops demonstrate that ZnS:0.05Mn nanoparticles exhibit ferromagnetic ordering below 30 K, unlike its bulk counterpart. No magnetic field dependence of the Mn2+ PL intensity is observed up to 1 T. ...