Erbium Luminescence Research Articles

Special features of the excitation spectra and kinetics of photoluminescence of the Si1 − x Ge x :Er/Si structures with relaxed heterolayers

Luminescent properties of heteroepitaxial Si1 − xGex:Er/Si structures with relaxed heterolayers are studied. The results of combined studies of the excitation spectra and kinetics of photoluminescence (PL) are used to single out the components providing the largest contribution to the PL signal of the Si1 − xGex:Er/Si structures in the wavelength region of 1.54 μm. It is shown that relaxation of elastic stresses in the Si1 − xGex:Er heterolayer affects only slightly the kinetic characteristics of erbium luminescence and manifests itself in insignificant contribution of the defects and defect-impurity complexes to the luminescent response of the Si1 − xGex:Er/Si structures. In the excitation spectra of the erbium PL, special features related to the possibility of the rare-earth impurity excitation at energies lower than the band gap of the Si1 − xGex solid solution are revealed. It is shown that a peak the width of which depends on the band gap of the solid solution and the extent of its relaxation is observed in the excitation spectra of the erbium-related PL in the Si1 − xGex:Er/Si structures in the wavelength region of 1040–1050 nm. The observed specific features are accounted for by involvement of intermediate levels in the band gap of the Si1 − xGex:Er solid solution in the process of excitation of an Er3+ ion.

Whispering gallery modes at 800 nm and 1550 nm in concentric Si-nc/Er:SiO2 microdisks

We examined a concentric Si nanocrystal (Si-nc) and Er doped SiO2 (Er:SiO2) microdisk structure supporting high-Q whispering gallery modes (WGMs) at both visible and telecom wavelengths. This structure provides a means to utilize Si-nc luminescence as an optical pump for an Er:SiO2 cavity without subjecting a telecom-wavelength, Er:SiO2-based mode to loss mechanisms associated with the Si-nc material. After fabricating a concentric microdisk consisting of an inner Si-nc disk and an outer Er:SiO2 ring, we characterize visible wavelength WGMs excited by the Si-nc photoluminescence and observed spectrometer limited quality factors as high as 103. Telecom wavelength photoluminescence from the Er:SiO2 ring was measured to have a quality factor as high as 104 in the erbium luminescence region using a passive pulled fiber setup.

Probing the Complexities of the Sensitization of Erbium Luminescence by Silicon Nanoclusters - Time Resolved Measurements, Nanocluster Nucleation, and the Role of Stress.

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Influence of the silicon nanocrystal size on the 1.54 μm luminescence of Er-doped SiO/SiO2 multilayers

The influence of the silicon nanocrystal (Si-nc) size on the erbium luminescence at 1.54 μm was studied in Er-doped silicon oxide thin films containing Si-nc. Er-doped and undoped SiO/SiO2 multilayers were prepared to control the Si-nc size. The results showed that the Er luminescence was due to an energy transfer process between Si-nc and Er ions. The proportion of Si-nc which couples with Er was dependent on the Si-nc size and the energy transfer process is maximal for a size equal to 4 nm. This preferentially coupling effect is interpreted by the existence of an optimum overlap between the Si-nc emission spectrum and the I49/2 multiplet of Er ions.

Enhanced light emission in photonic crystal nanocavities with Erbium-doped silicon nanocrystals

Photonic crystal nanocavities are fabricated in silicon membranes covered by thermally annealed silicon-rich nitride films with Erbium-doped silicon nanocrystals. Silicon nitride films were deposited by sputtering on top of silicon on insulator wafers. The nanocavities were carefully designed in order to enhance emission from the nanocrystal sensitized Erbium at the 1540nm wavelength. Experimentally measured quality factors of ∼6000 were found to be consistent theoretical predictions. The Purcell factor of 1.4 was estimated from the observed 20-fold enhancement of Erbium luminescence.

Synthesis and spectroscopic properties of monocyclic and bicyclic erbium phtalocyanines

Bimacrocyclic and monomacrocyclic erbium phtalocyanines have been synthesized and their luminescence spectra and lifetimes have been studied. The bi-planar structure of ErPc2 complexes, although interesting at first sight, is non-luminescent because of a strong absorption band near 1.5 μm. However, the luminescence of the erbium ion can be recovered after oxidation or reduction of the macrocycle. Monomacrocyclic erbium phtalocyanines exhibit a strong luminescence of erbium as a result of the energy transfer between the excited phtalocyanine macrocycle and the erbium ion. With a perchlorinated phtalocyanine and a perdeuterated axial ligand in a deuterated solvent, the luminescence lifetime reaches 5 μs, which is the maximum lifetime found for conventional perdeutarated ligands. The large absorption cross-section of phtalocyanine in the red may counterbalance the fast luminescence lifetime, allowing the hope for a new all-organic integrated optical amplifier device.

Generalized rate-equation analysis of excitation exchange between silicon nanoclusters and erbium ions

We discuss the use of rate equations to analyze the sensitization of erbium luminescence by silicon nanoclusters. In applying the general form of second-order coupled rate-equations to the Si nanocluster-erbium system, we find that the photoluminescence dynamics cannot be described using a simple rate equation model. Both rise and fall times exhibit a stretched exponential behavior, which we propose arises from a combination of a strongly distance-dependent nanocluster-erbium interaction, along with the finite size distribution and indirect band gap of the silicon nanoclusters. Furthermore, the low fraction of erbium ions that can be excited nonresonantly is a result of the small number of ions coupled to nanoclusters.

Silicon nanoclusters containing nitrogen and sensitization of erbium luminescence in SiO x:Er

Silicon-rich silica samples doped with erbium were grown by PECVD and characterized by photoluminescence, time-resolved photoluminescence and Fourier transform infrared spectroscopy. We observe that upon increased silicon content, the absorption spectrum reveals the formation of a Si N bond. This indicates the possible incorporation of nitrogen from the precursor N 2O gas into the Si nanoclusters. The highest erbium photoluminescence is obtained for the sample with the highest silicon content and its decay characteristics are nearly single exponential with a time constant of 5 ms. In addition to erbium emission, a visible luminescence peak at about 550 nm is observed. This shows multi-exponential decay kinetics with decay times of the order of 10 ns. We propose that this emission is due to small Si nanoclusters covered by a Si N shell. From the measurements, we study a mechanism to explain the erbium excitation in this material.

Infrared luminescence quenching in erbium(iii) tris(8-quinolinolate): an ab initio approach

We present here an ab initio calculation of the quenching rate of erbium luminescence by the ligand C–H vibrations in erbium(III) tris(8-quinolinolate) within the framework of energy-transfer theory. The C–H vibrational transition matrix elements are evaluated on the basis of DFT calculations of the quinolate ligand at the B3LYP/6-311++G(2d, 2p) level of theory. The luminescence lifetime calculated by considering the dipole–dipole and quadrupole–dipole interaction mechanisms is in good agreement with the experimental value. Based on the theoretical results for the complex, the dependence of the luminescence quenching rates on the distance between the erbium ion and the C–H bond is generalized and discussed, and comparisons with available experimental results are made.

Quenching of IR Luminescence of Erbium, Neodymium, and Ytterbium β-Diketonate Complexes by Ligand C−H and C−D Bonds

The effect of CH and CD quenching on the luminescence lifetime of Er(3+) Nd(3+) and Yb(3+) in the Cs[Ln(HFA)(4)] system has been quantified, and we have shown that for Er(3+) ions the quenching is dominated by the nearest neighbor CH oscillators, whereas for Nd(3+) ions the roles of more distant CH oscillators and nearest neighbor CD oscillators are important.

Theoretical modeling of excitation and de-excitation processes of Er in SiO 2 with Si nanocrystals

We construct the theory of carriers confined in Si quantum dots with finite energy barriers for electrons and holes in the framework of the multiband effective mass theory. We apply this theory for theoretical modeling of the excitation of erbium inside and outside of Si nanocrystals in SiO 2 matrix due to the Auger process induced by the recombination of a confined electron–hole pair as well as the intraband transitions of “hot” confined carriers. Auger de-excitation processes of the Er 3+ ion leading to the quenching of erbium luminescence are discussed as well.

Self-assembling of supramolecular erbium–oxygen clusters in magnetron plasma, and the optimization of erbium luminescence in a-SiOx:H〈Er, O〉 films

Films of erbium-doped amorphous hydrogenated silicon a-SiOx:H〈Er,O〉 were fabricated by dc-magnetron sputtering at different concentrations of oxygen in the magnetron plasma and different areas of erbium metallic target. It was demonstrated that the increase of oxygen concentration in the plasma gaseous phase above ∼5mol% leads to a sharp rise in the amount of oxygen bound to erbium in the a-SiOx:H〈Er,O〉 films. Simultaneously, a smooth increase in the concentration of oxygen bound to matrix-forming elements (silicon, hydrogen) is observed. The increase of the area of erbium target, corresponding to the rise of concentration of erbium ions in the plasma, also favors the binding of erbium with oxygen. However, the content of erbium in the a-SiOx:H〈Er,O〉 film (in atomic percents) significantly drops with intense binding of erbium with oxygen. These facts point to the formation of erbium–oxygen clusters, with a large number of oxygen atoms, which are probably formed in the magnetron plasma but are deposited as a separate species on the substrate in the reaction chamber. The intensity of erbium photoluminescence rises significantly in the region of formation of these large erbium–oxygen clusters. A ‘phase-transition’ model is formulated, describing the properties of a-SiOx:H〈Er,O〉 films, based on the assumption of the formation of large erbium–oxygen clusters in the magnetron plasma. The size and composition of these clusters are determined. The model is semi-quantitatively consistent with all the experimental findings.

Effect of B 2O 3 on luminescence of erbium doped tellurite glasses

The B 2O 3 was introduced into the Er 3+ doped TeO 2–ZnO–Na 2O glass to increase the phonon energy of the host. The effect of B 2O 3 on the non-radiative rate of the 4I 11/2 → 4I 13/2 transition of Er 3+, the lifetime of the 4I 11/2 and 4I 13/2 levels, the green and red upconversion emissions intensity, and the 4I 13/2 → 4I 15/2 emission intensity was discussed. The results show that the phonon energy of boro-tellurite glass is close to that of germanate glass and is quite smaller than that of borate glass. The lifetime of 4I 11/2 level and the upconversion emissions decrease with increasing B 2O 3 concentration. The higher OH group concentration presented in the boro-tellurite glass may shorten the lifetime of 4I 13/2 level and also reduce the quantum efficiency of 4I 13/2 → 4I 15/2 emission. The future dehydrating procedures are suggested to enhance the efficiency of amplification at 1.5 μm band.

Carrier-induced quenching processes on the erbium luminescence in silicon nanocluster devices

The luminescence-quenching processes limiting quantum efficiency in Er-doped silicon nanocluster light-emitting devices are investigated and identified. It is found that carrier injection, while needed to excite Er ions through electron-hole recombination, at the same time produces an efficient nonradiative Auger deexcitation with trapped carriers. This phenomenon is studied in detail and, on the basis of its understanding, we propose device structures in which sequential injection of electrons and holes can improve quantum efficiency by avoiding Auger processes.

Sensitisation of erbium luminescence in erbium-implanted alumina

Abstract Experimental evidence of an efficient broadband sensitisation mechanism in erbium-implanted alumina is presented. Alumina thin films were deposited by plasma-enhanced chemical vapour deposition. The as-grown films were implanted with erbium. Photoluminescence excitation spectra showed that erbium-implanted alumina thin films exhibit 1.53 μm luminescence even when pumped at wavelengths outside Er 3+ absorption bands. The samples were analysed structurally using transmission electron microscopy and electron energy loss spectroscopy. We postulate that the sensitising species is either small nanoclusters of aluminium or pairs of aluminium ions, though the possibility of defect-mediated sensitisation cannot be conclusively ruled out at this stage.

An hybrid organic–inorganic approach to erbium-functionalized nanodots for emission in the telecom window

A new class of hybrid materials for efficient laser emission and amplification in the 1.55 μm eye-safe telecommunication window has been designed, elaborated and characterized, based on lanthanide-doped yttrium oxide nanoparticle guests embedded in a polymer host matrix. The average size of these nanocrystals can be finely tuned by controlling the relative quantities of an organic fuel (glycine) with respect to the yttrium- and lanthanide-containing reactants involved in the combustion reaction leading to nanoparticle synthesis. Two complementary sensitizers have been added to Er/Y 2O 3 nanocrystals in order to improve the Erbium luminescence efficiency: cerium to increase population inversion between the emitting and the ground state by accelerating the de-excitation process from the 4I 11/2 initially uppermost excited state at 980 nm down to 4I 13/2 state emitting around 1.55 μm, and ytterbium to improve the pumping efficiency of the material owing to its strong absorption cross section at 980 nm and subsequent efficient energy transfer towards the 4I 11/2 state of erbium ion. Y 2O 3 nanoparticles with an optimized erbium–ytterbium composition have been incorporated in a PMMA polymer matrix, resulting in a hybrid amorphous material displaying high gain coefficient values (up to 30 cm −1 as from Amplified Spontaneous Emission experiments) upon moderate 980 nm pumping intensities. These materials open attractive perspectives in the domain of polymer-based telecom amplifiers, with the additional asset of multifunctional properties whereby gain originating from the inorganic Y 2O 3 nanocrystals can be associated to nonlinear responses attached to an adequately functionalized polymer host matrix.

Erbium luminescence properties of niobium-rich oxide glasses

Erbium luminescence has been investigated in niobium borophosphate glass. A correlation between luminescence intensity at 1532 nm, OH absorption and the structure of the glass network was established as a function of the niobium oxide concentration. An increase of the radiative efficiency corresponding to 4I 13/2 → 4I 15/2 (4f–4f) transition of Er 3+ ions has been observed for niobium richest glasses. The modification of the Er 3+ ions site is analyzed as a function of the niobium concentration. A Judd–Ofelt analysis has been applied to emphasize the structural change. An increase of the up conversion was also measured as the niobium oxide content increases.

Effect of niobium oxide introduction on erbium luminescence in borophosphate glasses

Abstract The role of the addition of niobium oxide in large amount on the Er 3+ emission properties at 1535 nm for excitation at 980 nm in borophosphate glass has been investigated. An increase of the emission, associated with a decrease of the lifetime of the 4 I 13/2 erbium level and a larger absorption cross section of erbium and ytterbium at 980 nm was evidenced. Changes induced on hydroxyl groups absorption with addition of Nb 2 O 5 in glasses was clearly shown by IR Spectroscopy in the range 2500–3700 cm −1 . The relationship between erbium luminescence at 1535 nm, Nb 2 O 5 concentration and OH group nature in niobium borophosphate glasses has been discussed. A fluorination treatment, conducted to reduce the OH group content, has allowed the reduction of the absorption coefficient at 3000 cm −1 by half. Amplification measured at 1535 nm has confirmed the beneficial effect of the Nb 2 O 5 introduction on the gain and has been found to be in accordance with the evolution of the luminescence properties.

Erbium in Semiconductors: Where are we coming from; Where are we going?

AbstractIt is one of the curious twists of technology that transitions which are parity forbidden in the free ions of rare earths should have become of immense importance in solids used in fluorescent lighting, cathode ray tubes and optical amplifiers. It is not an unreasonable expectation that having achieved such success with excitation from photons and accelerated electrons that junction electroluminescence should also be important. Since Ennen demonstrated good low temperature electroluminescence in silicon in the early 80's, a formidable amount of work has been done to try to understand the excitation and quenching mechanisms in common semiconductor hosts such as silicon and gallium arsenide. Although some remarkable experimental results have been obtained for erbium in nanostructures, insulators and wide bandgap materials the performance in bulk silicon and silicon germanium is disappointing. More importantly we still have not achieved a comprehensive, detailed understanding of the processes of non-radiative competition to the rare earth emission. In this paper the key steps that have been made over the last twenty years towards our present day knowledge of erbium luminescence in semiconducting hosts are reviewed and an assessment made of what remains to be done.

Strong erbium luminescence in the near-infrared telecommunication window

A new type of near-infrared emitting rare-earth complex has been synthesised, consisting of three bis(perfluoroalkylsulfonyl)imide ligands and one 1,10-phenanthroline molecule. The chelate rings formed by the rare-earth ion and the bidentate ligands do not contain any carbon atoms and can hence be considered as ‘inorganic’ chelate rings. The absence of C–H stretching vibration modes in the first coordination sphere of the rare-earth ion and the presence of a light-harvesting moiety (1,10-phenanthroline) bound to the rare-earth ion result in a complex that can be efficiently excited and exhibits intense near-infrared luminescence.