U. Hömmerich

Demonstration of room-temperature laser action at 2.5 µm from Cr 2+ :Cd 0.85 Mn 0.15 Te

Room-temperature laser action from Cr(2+)-doped Cd(0.85)Mn(0.15)Te has been demonstrated for what is believed to be the first time. We achieved pulsed laser operation centered at ~2.5mu m by pumping into the mid-infrared absorption band of Cr(2+) ions by use of the 1.907- mum output of a H(2) Raman-shifted Nd:YAG laser. The output of the free-running Cr(2+):Cd(0.85)Mn(0.15)Te laser had a width of ~50 nm (FWHM), and the slope efficiency was calculated to be 5.5% under nonoptimum conditions.

Visible Laser Action of Dy3+ Ions in Monoclinic KY(WO 4) 2 and KGd(WO 4) 2 Crystals under Xe-Flashlamp Pumping

Pulsed laser action in the novel visible laser channels 4F9/2→6H13/2 (at ≈0.57 µm) and 4F9/2→6H11/2 (at ≈0.66 µm) of Dy3+ ions in monoclinic KY(WO4)2 and KGd(WO4)2 single crystals at nitrogen cryogenic temperature under Xe-flashlamp pumping is excited for the first time. All observed lasing emissions are identified. Some spectroscopic characteristics of the investigated crystals are also presented.

Photoluminescence properties of in situ Tm-doped AlxGa1−xN

We report on the photoluminescence (PL) properties of in situ Tm-doped AlxGa1−xN films (0⩽x⩽1) grown by solid-source molecular-beam epitaxy. It was found that the blue PL properties of AlxGa1−xN:Tm greatly change as a function of Al content. Under above-gap pumping, GaN:Tm exhibited a weak blue emission at ∼478 nm from the 1G4→3H6 transition of Tm3+. Upon increasing Al content, an enhancement of the blue PL at 478 nm was observed. In addition, an intense blue PL line appeared at ∼465 nm, which is assigned to the 1D2→3F4 transition of Tm3+. The overall blue PL intensity reached a maximum for x=0.62, with the 465 nm line dominating the visible PL spectrum. Under below-gap pumping, AlN:Tm also exhibited intense blue PL at 465 and 478 nm, as well as several other PL lines ranging from the ultraviolet to near-infrared. The Tm3+ PL from AlN:Tm was most likely excited through defect-related complexes in the AlN host.

Slope efficiency and tunability of a Cr2+: Cd0.85Mn0.15Te mid-infrared laser

Abstract Efficient and widely tunable mid-infrared laser operation from Cr 2+ : Cd 0.85 Mn 0.15 Te was demonstrated. The pulsed Cr 2+ : Cd 0.85 Mn 0.15 Te laser was tuned using a quartz birefringent filter in a spectral range from 2300–2600 nm. Free running laser action centered at ∼2660 nm was achieved using a set of mid-infrared laser mirrors on CaF 2 substrates. The maximum slope efficiency obtained for the free-running laser using an uncoated crystal was 44.2%.

Photoluminescence study of Er-doped AlN

Abstract We present a photoluminescence (PL) study of Er-doped AlN epilayer on sapphire substrate. The AlN : Er film was grown by metalorganic molecular beam epitaxy and an Er concentration of 2–5 × 1019Er/cm3 was obtained. Following the excitation of an argon ion laser at 488 nm, we observed a strong 1.54 μm Er3+ luminescence, which is quenched by only a factor of two between 15 K and room temperature. The photoluminescence excitation (PLE) spectrum, as well as PL lifetime measurement suggest that at 488 nm, Er3+ is excited through a photo-carrier mediated process. In contrast, exciting AlN : Er at ~525 nm seems to result in the direct excitation of an intra-4f transition of Er3+.

Effect of Si codoping on Eu3+ luminescence in GaN

Eu and Si codoped GaN thin films were grown on sapphire by solid source molecular beam epitaxy. Eu3+ photoluminescence (PL) emission at ∼622 nm (D50-F72) was enhanced by approximately five to ten times with Si doping. The effect of Si codoping on PL intensity, lifetime, and excitation dependence revealed two distinct regimes. Moderate Si doping levels (0.04–0.07 at. %) lead to an increase in lifetime combined with improved excitation efficiency and a greatly enhanced PL intensity. High Si doping levels (0.08–0.1 at. %) significantly quench the PL intensity and lifetime, due primarily to nonradiative channels produced by a high defect population.

A spectroscopic study on the luminescence of Er in porous silicon

We report a spectroscopic study on the photoluminescence (PL) of erbium implanted into porous silicon (Er:PSi). Two different porous Si samples were implanted with a dose of 1015 Er/cm2 at 380 keV and annealed at 650 °C for 30 min under identical conditions. Both samples exhibited Er3+ luminescence at 1.54 μm, which was quenched by less than a factor of two between 15 K and room temperature. Visible PL studies of Er implanted and annealed porous Si samples showed broad spectra which peaked at ∼700 nm for sample A and peaked at ∼660 nm for sample B. Sample A showed a four times stronger Er3+ luminescence than that observed from sample B. In contrast, temperature quenching of the Er3+ luminescence was found to be similar or slightly weaker from sample B than from sample A. The spectroscopic data will be discussed in terms of the excitation mechanisms of Er3+ in porous Si nanostructures.

Luminescence characteristics of Er-doped GaN semiconductor thin films

Abstract Semiconductors doped with rare earth atoms have been studied for more than a decade because of the potential of using them to develop compact and efficient electroluminescence (EL) devices. Trivalent erbium ions (Er 3+ ) are of special interest because they exhibit atomic-like transitions centered at 1540 nm, which corresponds to the low-loss window of silica-based optical fibers. While EL devices, based on Er-doped Si and GaAs materials, have been fabricated, their efficiency remains too low for practical applications. Several years ago an important observation was made that there was less detrimental temperature quenching of Er luminescence intensity for larger bandgap host materials. Therefore, Er-doping of wide gap semiconductors, such as the III–V nitrides, appears to be a promising approach to overcoming the thermal quenching of Er luminescence found in Si and GaAs. In particular, GaN epilayers doped with Er ions have shown a highly reduced thermal quenching of the intensity of the Er luminescence from cryogenic to elevated temperatures. The remarkable thermal stability of the light emission may be due to the large energy bandgap of the material, as well as to the optical inactivity of the material defects in the GaN films. In this paper, recent data concerning the luminescence characteristics of Er-doped GaN thin films are presented. Two different methods have been used for Er-doping of the GaN films: ion implantation and in situ doping during epitaxial growth. Both methods have proven successful for incorporation and optical activation of Er 3+ ions. Infrared photoluminescence spectra, centered at 1540 nm, have been measured for various Er-doped III–N films. Considerably different emission spectra, with different thermal quenching characteristics, have been observed, depending upon the wavelength of the optical pump and the Er-doping method. Defect-related absorption centers permit excitation of the Er ions using below-bandgap optical sources. Elemental impurities, such as O and C, in the thin films have also been shown to influence the emission spectra and to lead to different optical characteristics.

Correlation between visible and infrared (1.54 μm) luminescence from Er‐implanted porous silicon

A photoluminescence excitation (PLE) study was performed of Er‐implanted porous Si with two different porosities. Erbium was implanted at a dose of 1×1015 cm−2 at 380 keV and the samples were annealed for 30 min at temperatures from 650 to 850 °C. We observed that PLE spectra from Er3+ at 1.54 μm are nearly identical to those from the visible‐emitting porous Si layers. Our results provide the first direct experimental evidence that infrared photoluminescence at 1.54 μm arises from Er3+ ions in porous Si and that ions are excited through the recombination of excess carriers spatially confined in Si nanograms.

Luminescence enhancement in AlN(Er) by hydrogenation

Room-temperature Er3+ photoluminescence increases of a factor of 5 are observed for AlN(Er) samples treated in a 2H plasma at 200 °C for 30 min. The atomic deuterium passivates defects in the AlN, which normally provide alternative carrier recombination routes. Postdeuteration annealing at 300 °C for 20 min removes the luminescence enhancement by depassivating the nonradiative centers. The AlN(Er) provides a high degree of resistance to thermal quenching of luminescence as a function of temperature because of its wide band gap (6.2 eV), and hydrogenation is a simple method for maximizing the optical output in this materials system.