Ei Ei Nyein

Spectral and Time-Resolved Photoluminescence Studies of Eu-Doped GaN

We report on spectral and time-resolved photoluminescence (PL) studies performed on Eu-doped GaN prepared by solid-source molecular-beam epitaxy. Using above-gap excitation, the integrated PL intensity of the main Eu3+ line at 622.3 nm (5D0→7F2 transition) decreased by nearly 90% between 14 K and room temperature. Using below-gap excitation, the integrated intensity of this line decreased by only ∼50% for the same temperature range. In addition, the Eu3+ PL spectrum and decay dynamics changed significantly compared to above-gap excitation. These results suggest the existence of different Eu3+ centers with distinct optical properties. Photoluminescence excitation measurements revealed resonant intra-4f absorption lines of Eu3+ ions, as well as a broad excitation band centered at ∼400 nm. This broad excitation band overlaps higher lying intra-4f Eu3+ energy levels, providing an efficient pathway for carrier-mediated excitation of Eu3+ ions in GaN.

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.

Photoluminescence in erbium doped amorphous silicon oxycarbide thin films

Photoluminescence (PL) in Er-doped amorphous silicon oxycarbide (a-SiCxOy:Er) thin films, synthesized via thermal chemical vapor deposition, was investigated for carbon and oxygen concentrations in the range of 0–1.63. Intense room-temperature PL was observed at 1540 nm, with the PL intensity being dependent on the carbon and oxygen content. The strongest PL intensity was detected for a-SiC0.53O0.99:Er when pumped at 496.5 nm, with ∼20 times intensity enhancement as compared to a-SiO2:Er. Broadband excitation in the visible was observed for a-SiC0.53O0.99:Er. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses suggest that the formation of Si–C–O networks plays an important role in enhancing the Er optical activity in a-SiCxOy:Er films.

Infrared to visible upconversion of Nd 3+ ions in KPb 2 Br 5 low phonon crystal

In this work we present a detailed analysis of the infrared to visible upconversion in Nd(3+)-doped KPb(2)Br(5) low phonon crystal by using both steady-state and time-resolved luminescence spectroscopy. Efficient blue, green, orange, and red emissions have been observed under excitation into the (4)F(5/2) and (4)F(3/2) states. The low phonon energy of this crystal leads to a significant reduction of the multiphonon relaxation rates which allows most of the excited states to relax radiatively. To investigate the nature of the upconversion processes, emission spectroscopy and lifetime measurements for the visible fluorescence, performed by using one photon excitation, have been compared to the upconverted emissions and lifetimes obtained under infrared pulsed excitation. The analysis of the experimental results indicates that the upconverted emissions occur via energy-transfer upconversion.

Excitation-Wavelength Dependent and Time-Resolved Photoluminescence Studies of Europium Doped GaN Grown by Interrupted Growth Epitaxy (IGE)

Abstract : The emission properties of Eu doped GaN thin films prepared by interrupted growth epitaxy (IGE) were investigated through excitation-wavelength dependent and time-resolved photoluminescence (PL) studies. Under above-gap excitation (333-363 nm) large differences were observed in the Eu3(+) PL intensity and spectral features as a function of Ga shutter cycling time. The overall strongest red Eu(3+) PL intensity was obtained from a sample grown with a Ga-shutter cycling time of 20 minutes. The main Eu(3+) emission line originating from (5)D(sub 0) -> (7)F(sub 2) transition was composed of two peaks located at 620 nm and 622 nm, which varied in relative intensity depending on the growth conditions. The room-temperature emission lifetimes of the samples were non-exponential and varied from ~50 s to ~200 s (1/e lifetimes). Under resonant excitation at 471 nm [(7)F(sub 0) -> (5)D(sub 2)] all samples exhibited nearly identical PL spectra independent of Ga shutter cycling time. Moreover, the Eu(3+) PL intensities and lifetimes varied significantly less compared to above-gap excitation. The excitation wavelengths dependent PL results indicate the existence of different Eu(3+) centers in GaN: Eu, which can be controlled by the Ga shutter cycling time.

Materials Development for Mid-IR Solid-State Lasers

Solid-state lasers operating in the mid-IR wavelength region (3-5 mum) continue to be of great current interest for applications in laser remote sensing of chemical and biological agents, IR countermeasures, and bio-medical procedures. The development of mid-IR solid-state lasers based on oxide and fluoride crystals is hampered by large non-radiative decay rates through multi-phonon emission. On the contrary, rare earth (RE) doped crystals with low maximum phonon energies have shown efficient mid-IR emission as well as lasing at room temperature [1-9]. Examples of emission transitions in the 3-5 mum spectral region are indicated in Fig. 1 for the rare earth ions Pr3+, Nd3+, Dy3+ and Er3+.

Spectroscopy and frequency upconversion in KPb 2 Br 5 :Nd 3+ crystal

In this work we present a detailed analysis of the room temperature infrared to visible upconversion in Nd3+-doped KPb2Br5 crystal by using both steady-state and time-resolved luminescence spectroscopy. The study includes one photon absorption and emission spectroscopy and lifetime measurements for the visible and infrared fluorescence, and infrared to, blue, green, orange, and red upconversion processes. The possible upconversion mechanisms are discussed in terms of excitation spectra, excitation power dependence, and lifetimes of the upconversion emissions.

Mid-infrared (3-5 μm) emission from rare earth doped KPb 2 Br 5

Solid-state lasers operating in the mid-infrared (MIR) wavelength region (3-5 μm) are of significant current interest for laser remote sensing of chemical and biological agents as well as for military countermeasures. The development of MIR solid-state lasers based on oxide and fluoride laser hosts is limited by non-radiative decay through multi-phonon relaxations. Rare earth doped crystals with low maximum phonon energies can exhibit efficient MIR emission at room temperature. In this paper, we present results of the material synthesis and optical properties of rare earth (Pr, Nd, Dy, Er) doped KPb2Br5, which has a maximum phonon energy of only ~140 cm-1.

Spectroscopy and frequency up-conversion in KPb2Br5:Nd3+ crystal

In this work we present a detailed analysis of the room temperature infrared to visible upconversion in Nd3+-doped KPb2Br5 crystal by using both steady-state and time-resolved luminescence spectroscopy. The study includes one photon absorption and emission spectroscopy and lifetime measurements for the visible and infrared fluorescence, and infrared to, blue, green, orange, and red upconversion processes. The possible upconversion mechanisms are discussed in terms of excitation spectra, excitation power dependence, and lifetimes of the upconversion emissions.

Visible and Infrared Emission from Er-doped III-N Light Emitting Diodes

We report on the visible and infrared emission characteristics of Er-doped III-N lightemitting diodes (LEDs). Quantum well-like device structures were grown through a combination of metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) on cplane sapphire substrates. The dual stage growth process was used to take advantage of the high quality of AlGaN layers produced by MOCVD and in situ doping of Er during MBE growth. The multilayer structures were processed into devices and LEDs with different sizes and geometric shapes were produced. Electroluminescence (EL) was observed under either forward or reverse bias conditions. Visible and infrared spectra displayed narrow emission lines representative of the Er 3+ system. The temperature dependence of the spectra, which were measured from 100K to 300K, showed a stability in the visible emission intensity but a sharp decrease in the infrared intensity at room temperature. Based on light output vs current measurements, estimates of the excitation cross-section were obtained for visible EL emission.