Μm Emission Intensity Research Articles

Enhancing erbium emission by strain engineering in GaN heteroepitaxial layers

Much research has been devoted to the incorporation of erbium (Er) into semiconductors aimed at achieving photonic integrated circuits with multiple functionalities. GaN appears to be an excellent host material for Er ions due to its structural and thermal stability. Er-doped GaN (GaN:Er) epilayers were grown on different templates, GaN/Al2O3, AlN/Al2O3, GaN/Si (111), and c-GaN bulk. The effects of stress on 1.54 μm emission intensity, caused by lattice mismatch between the GaN:Er epilayer and the substrate, were probed. The emission intensity at 1.54 μm increased with greater tensile stress in the c-direction of the GaN:Er epilayers. These results indicate that the characteristics of photonic devices based on GaN:Er can be optimized through strain engineering.

1.54 μ m emission mechanism in Er-doped silicon-rich silicon oxides

Silicon-rich silicon oxide (SRSO) and Er-doped SRSO (SRSO:Er) thin films were formed by pulsed laser deposition, and characterized by photoluminescence (PL), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and UV-visible transmission in order to clarify the 1.54 μm emission mechanism in the SRSO:Er films. The oxygen content of the films was varied by the adjustment of oxygen partial pressure. The behavior of the 1.54 μm PL with oxygen partial pressure combined with XPS and XRD data show that the 1.54 μm emission intensity is related to the amount of SiOx phase. This conclusion is well supported by the measurements of UV-visible transmission. In many previous papers, the 1.54 μm emission is associated with Si nanocrystals, but in our study the correlation between 1.54 μm emission intensity and the amount of SiOx phase is much clearer.

Photoluminescence properties of erbium doped InGaN epilayers

We report on the photoluminescence properties of erbium (Er) doped InxGa1−xNa epilayers synthesized by metal organic chemical vapor deposition. The crystalline quality and surface morphology of Er doped In0.05Ga0.95N were nearly identical to those of Er doped GaN. The photoluminescence intensity of the 1.54 μm emission in Er doped In0.05Ga0.95N was an order of magnitude lower than in Er doped GaN and decreased with the increase of the In content. The reduction in 1.54 μm emission intensity was accompanied by enhanced emission intensities of deep level impurity transition lines.

Investigation of 2.0 μm emission in Tm 3+ and Ho 3+ co-doped oxyfluoride tellurite glass

This paper reports 2.0 μm emission properties of Tm 3+/Ho 3+ co-doped oxyfluoride tellurite glass exited by 808 nm laser diode (LD). Mid-infrared transmittance property of glass was investigated by Fourier transform infrared (FTIR) spectrometer. The real chemical composition of investigated glass was identified by X-ray photoelectric spectroscopy (XPS). Thermal stability of the glass was determined by differential thermal analysis (DTA) measurement. The Judd–Ofelt parameters, spontaneous radiative transition probabilities, branching ratios and radiative lifetime of Ho 3+ were calculated based on the absorption spectra by using Judd–Ofelt theory. Results indicate that the maximum 2.0 μm emission intensity attributed to the 5I 7→ 5I 8 transition of Ho 3+ was achieved at 1.5 mol% Tm 2O 3 and 1 mol% Ho 2O 3 concentrations in oxyfluoride tellurite glass. OH − absorption at 3000 cm −1 was greatly depressed by introduction of 10 mol% F −. The maximum absorption and stimulated emission cross-section of Ho 3+ near 2.0 μm are 7.0×10 −21 cm 2 at 1950 nm and 8.8×10 −21 cm 2 at 2048 nm, respectively. The calculated radiative lifetime of 4.4 ms for 5I 7→ 5I 8 transition and large stimulated emission cross-section of the Tm 3+/Ho 3+ co-doped oxyfluoride tellurite glass indicate that the glass has a potential application in efficient 2.0 μm laser.

Current-injected 1.54μm light emitting diodes based on erbium-doped GaN

Current-injected 1.54μm emitters have been fabricated by heterogeneously integrating metal organic chemical vapor deposition grown Er-doped GaN epilayers and 365nm nitride light emitting diodes. It was found that the 1.54μm emission intensity increases almost linearly with input forward current. The results represent a step toward demonstrating the feasibility for achieving electrically pumped optical amplifiers for optical communication that possess advantages of both semiconductor optical amplifiers and Er-doped fiber amplifiers.

Preparation and performance of Cr3+/Tm3+/Ho3+ co-doped fluorophosphate glasses

Fluorophosphate glasses with various Al(PO3)3 contents were prepared，and their structure,thermal properties and spectral properties were studied.The emission properties at around 2.0μm of Cr3+/Tm3+/Ho3+ co-doped fluorophosphate glasses with different mole fractions of Tm3+ and Ho3+were studied. The spectral strength parameters Ωt(t=2,4,6) of those glasses have been calculated. Meanwhile,the spectral parameters, including the oscillator strength,spontaneous emission probability and branching ratios of Ho3+, have been calculated. The results show that the 2.0μm emission intensity gradually grows higher with the increase of the mole fraction of Tm3+. The Tm3+→(3F4) →Ho3+(5I7) energy transfer in (Tm3+/Ho3+) co-doped fluorophosphate glasses is very efficient, and it is dependent on the doping concentration.

Near- to Mid-Infrared Spectroscopy for the Giant Elliptical Galaxy NGC 1316 (Fornax A) with the AKARI Infrared Camera

We present the near- to mid-infrared (~2.5-13 μm) spectrum of the giant elliptical galaxy NGC 1316 (Fornax A) obtained with the Infrared Camera (IRC) on board AKARI. NGC 1316 is known to have a peculiar polycyclic aromatic hydrocarbon (PAH) emission spectrum with an unusually high ratio of the 11.3 μm to the 7.7 μm emission intensity through the Spitzer IRS observation. NGC 1316 is a 3 Gyr old merger remnant with a dormant nucleus that was rather active 0.1 Gyr ago; the relatively well-known evolutionary history makes the elliptical galaxy an ideal probe for studying long-term effects of past energetic events on the interstellar medium. We have found that there is no significant PAH emission feature at 3.3 μm while we have confirmed the peculiar PAH emission spectrum in the mid-infrared. We have detected a strong absorption feature at 4.3 μm, which may be attributed to solid-state CO2 in grain mantles. We discuss physical implications for those unusual emission and absorption features.

Thulium-sensitized neodymium in KPb2Cl5 for mid-infrared laser development

The energy transfer from Tm3+ to Nd3+ was explored in Tm,Nd:KPb_2Cl_5 for sensitization of a possible 5 µm Nd laser. Evidence for an efficient energy transfer from Tm3+ to Nd3+ under 785 nm excitation was obtained through monitoring changes in (i) the Tm^3+ decay behavior and (ii) the 5 µm emission intensity arising from the 4I_11/2-->4I_9/24 transition of Nd3+ ions. The quantum efficiency of the 5 µm emission from Nd3+ was estimated to be approximately four times greater in Tm,Nd:KPb_2Cl_5 compared with Nd:KPb2Cl5. Sensitization of Nd3+ with Tm3+ in KPb_2Cl_5 promises a significant increase in the maximum achievable slope efficiency of a potential 5 µm Nd laser.

Rare-earth doped chalcogenide glasses for fiber-optic amplifiers

Emission properties associated with the fiber-optic amplification in Ge–Ga–S–CsBr glasses were investigated. The intensity of the 1.31 μm emission from Dy3+ (6F11/2·6H9/2→6H15/2) increased sharply when the appropriate concentrations of alkali halides were added, at the expense of the 1.75 μm emission intensity (6H11/2→6H15/2). The lifetimes of the 1.31 μm emission level also increased up to 1580 μs. A small amount of As was added to increase the resistivity against the recrystallization during re-heating. The optimum composition for practical usage was 0.7[Ge0.25As0.10S0.65]–0.15GaS3/2–0.15CsBr. Phonon side band showed that the several local phonon modes, with the frequencies around 100 cm−1, were coupled to 4f electrons of Eu3+. The nearest neighbors of Eu3+ ions are composed of halogen ions that are part of well-structured complex such as tetrahedral [GaS3/2Br]− subunit and/or Ga2Br6.

An investigation of the morphological, electrical and optoelectronic properties of short chain Di-ureasils doped with Er3+ ions

Hybrid organic/inorganic xerogels containing Er3+ ions have been prepared by the solgel process. The hybrid framework of these compounds, designated as di-ureasils and represented by U(600), is composed of a siliceous backbone to which polyether chains containing 8.5 oxyethylene repeat units are linked through urea (-NHC(=O)NH-) bridges. The trivalent cations have been incorporated in the matrix as erbium triflate, Er(CF3SO3)3. Compositions with n (where n is the molar ratio of (OCH2CH2) repeat units per Er+ ion) between ∞ and 3 have been studied. The morphology of the materials was characterized by means of X-ray Diffraction and Differential Scanning Calorimetry. Complex Impedance spectroscopy was used to evaluate the levels of conductivity exhibited by the xerogels as a function of temperature. The results obtained clearly demonstrate the amorphous character of the samples analysed. At about 100 °C the most conducting sample is U(600)5Er(CF3SO3)3 (approximately 2×10−5 Scm−1), whereas the U(600)60Er(CF3SO3)3 compound displays the highest conductivity at room temperature (1×10−7 Scm−1). We have shown that concentration effects on the quenching of the 1.53 μm emission intensity (excited at 488 nm) are negligible. We have also shown that the Er3+ ions are active at room temperature.

Modification of the local phonon modes and electron–phonon coupling strengths in Dy 3+-doped sulfide glasses for efficient 1.3 μm amplification

The effect of changes in the local phonon modes and electron–phonon coupling strengths on the 1.31 μm fluorescence efficiency of Dy 3+-doped sulfide glass was investigated. An addition of 10 mole% CsBr resulted in a sharp increase in the 1.31 μm emission intensity at the expense of the 1.75 μm emission. The lifetime of the 1.31 μm emission level ( 6 F 11/2 – 6 H 9/2 ) increased to 1.58 ms, which was more than 40 times larger than that of the Ge–Ga–S host. Quantum efficiency increased from 17% to approximately 100%. These changes in the optical characteristics resulted from the large changes in the local phonon modes and electron-coupling strengths through the addition of CsBr to Ge 25Ga 10S 65 glass.

Er 3+ :Yb 3+ codoped lead fluoroindogallate glasses for mid infrared and upconversion applications

In this work, two sets of lead fluoroindogallate glasses were studied with the aim of using them as active media for laser devices at the mid infrared (∼2.8 μm) and visible (∼0.54 μm) regions. The infrared and upconverted emissions of Er3+ in single and Er3+:Yb3+ codoped samples were analyzed, and it was observed that the best set of samples for 2.8 μm emission was the single doped one, and that as the upconversion (anti-Stokes luminescence) increased as a function of Yb3+ concentration, the infrared emission decreased in the same manner. The results suggest that the codoping with Yb3+ favors only the upconversion processes which depopulate the I11/24 level, reducing the 2.8 μm emission intensity. On the other hand, the Yb3+ codoping will certainly increase the efficiency of an upconversion based device. Quantum efficiencies of infrared emissions and radiative lifetimes were calculated by using the Judd–Ofelt approximation. Er3+–Er3+ and Er3+–Yb3+ energy transfer efficiencies were calculated using the measured lifetimes of the levels involved in the energy transfer processes.

Origin of photoluminescence from Er3+ centers in erbium doped GaAs and Al0.4Ga0.6 As grown by MBE

Sharp erbium-related intra-4f shell luminescence from Er doped GaAs and Al0.4Ga0.6 As epitaxial layers grown by molecular beam epitaxy (MBE) is presented. The emission arising from the two Er3+ excited states,4I13/2 and4I11/2 are studied. We have observed, by means of heat treatment under differentambients such as As, Ga and Al over pressure, that the optically active Er3+ preferentially occupies a Column III lattice site or Column III related defects. The photoluminescence results of co-doping Al0.4Ga0.6As:Er with Si and Be by MBE is also reported for the first time. A strong single 1.54 μm spontaneous emission line is achieved by co-doping with Be (≈1×1018 cm−3). This improvement is a result of successfully eliminating or suppressing the other transitions without sacrificing the 1.54 μm emission intensity or linewidth.

IR emissions from UV excitation of benzene and methyl derivatives

IR emissions in the 3.1–3.8 μm region are observed from the photoexcitation of the vapor of benzene, toluene, xylenes, mesitylene and durene at 193 nm. All the molecules emit a band with a peak at 3.3 μm which is attributed to the ν = 1 → 0 transition of the aromatic CH stretching vibrational modes. In addition to the 3.3 μm band, an emission band with a peak at 3.43 μm is observed from the methyl derivatives which is attributed to the CH stretching vibrational modes of the CH 3 groups. This assignment is supported by the observation that the 3.43 μm emission intensity increases with the number of CH 3 groups in the methyl derivatives.