Near-infrared Luminescence Bands Research Articles

Near-IR Luminescence of Rare-Earth Ions (Er3+, Pr3+, Ho3+, Tm3+) in Titanate-Germanate Glasses under Excitation of Yb3.

Inorganic glasses co-doped with rare-earth ions have a key potential application value in the field of optical communications. In this paper, we have fabricated and then characterized multicomponent TiO2-modified germanate glasses co-doped with Yb3+/Ln3+ (Ln = Pr, Er, Tm, Ho) with excellent spectroscopic properties. Glass systems were directly excited at 980 nm (the 2F7/2 → 2F5/2 transition of Yb3+). We demonstrated that the introduction of TiO2 is a promising option to significantly enhance the main near-infrared luminescence bands located at the optical telecommunication window at 1.3 μm (Pr3+: 1G4 → 3H5), 1.5 μm (Er3+: 4I13/2 → 4I15/2), 1.8 μm (Tm3+: 3F4 → 3H6) and 2.0 μm (Ho3+: 5I7 → 7I8). Based on the lifetime values, the energy transfer efficiencies (ηET) were estimated. The values of ηET are changed from 31% for Yb3+/Ho3+ glass to nearly 53% for Yb3+/Pr3+ glass. The investigations show that obtained titanate–germanate glass is an interesting type of special glasses integrating luminescence properties and spectroscopic parameters, which may be a promising candidate for application in laser sources emitting radiation and broadband tunable amplifiers operating in the near-infrared range.

Spectroscopic Properties of Inorganic Glasses Doped with Pr3+: A Comparative Study.

The results presented in this communication concern visible and near-IR emission of Pr3+ ions in selected inorganic glasses, i.e., borate-based glass with Ga2O3 and BaO, lead-phosphate glass with Ga2O3, gallo-germanate glass modified by BaO/BaF2, and multicomponent fluoride glass based on InF3. Glasses present several emission bands at blue, reddish orange, and near-infrared spectral ranges, which correspond to 4f–4f electronic transitions of Pr3+. The profiles of emission bands and their relative intensity ratios depend strongly on glass-host. Visible emission of Pr3+ ions is tuned from red/orange for borate-based glass to nearly white light for multicomponent fluoride glass based on InF3. The positions and spectral linewidths for near-infrared luminescence bands at the optical telecommunication window corresponding to the 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3,3F4 transitions of Pr3+ are dependent on glass-host matrices and excitation wavelengths. Low-phonon fluoride glasses based on InF3 and gallo-germanate glasses with BaO/BaF2 are excellent candidates for broadband near-infrared optical amplifiers. Spectroscopic properties of Pr3+-doped glasses are compared and discussed in relation to potential optical applications.

Er3+-doped SiO2-based glasses – An exploration of structural, visible, chromatic, and NIR fluorescence characteristics

SiO2-based glasses doped with 1 mol% Er3+ were fabricated via melt-quench process and their structural and visible and NIR (near-infrared) fluorescence features have been investigated. Calculated Judd–Ofelt (J–O) intensity parameters that were deduced from absorption spectra are applied to reckon different radiative factors. Visible emission spectra and decay profiles (for 4S3/2 → 4I15/2 transition) were registered upon λexci.= 379 nm. CIE (Commission International de I'Eclairage), CCT (correlated color temperature), and CP (color purity) values were evaluated from the emission spectra. Also, a NIR luminescence band (4I13/2 → 4I15/2 transition) was identified by 980 nm LD (laser diode). Later, emission cross-section [(σemi) stimulated, (σMemi) from Mccumber theory] values were computed for observed NIR emission. Highest σemi and gain bandwidth (σemi × ∆λeff) were obtained to be 9.18×10−21 cm2 and 517×10−28 cm3 accordingly for 4I13/2 → 4I15/2 transition.

Polaron-Mediated Luminescence in Lithium Niobate and Lithium Tantalate and Its Domain Contrast

In this review article, we discuss photoluminescence phenomena mediated by polarons in lithium niobate (LNO). At first we present the fundamentals on polaron states in LNO and their energy levels, i.e., on free and bound electron polarons, on hole polarons as well as on bipolarons. We discuss the absorption measurements on reduced as well as on doped LNO that made the characterization of the formed polaron states possible by their absorption bands. Next, we proceed by reporting on the two polaron-mediated photoluminescence bands that have been observed in LNO: (1) A near-infrared luminescence band in the range of 1.5 eV shows a mono-exponential decay and a strong dependence on iron doping. This luminescence is emitted by bound polarons returning from an excited state to the ground state. (2) A luminescence band at visible wavelengths with a maximum at 2.6 eV shows a stretched-exponential decay and is strongly enhanced by optical damage resistant doping around the doping threshold. This luminescence stems from the recombination of free electron and hole polarons. The next major topic of this review are domain contrasts of the visible photoluminescence that have been observed after electrical poling of the substrate, as singly inverted domains show a slightly reduced and faster decaying luminescence. Subsequent annealing results in an exponential decrease of that domain contrast. We show that this contrast decay is strongly related to the mobility of lithium ions, thus confirming the role of polar defect complexes, including lithium vacancies, for these domain contrasts. Finally we discuss the extension of our investigations to lithium tantalate (LTO) samples. While the results on the domain contrast and its decay are similar to LNO, there are remarkable differences in their luminescence spectra.

A magneto-optical study of bismuth-doped MgO – Al2O3 – SiO2 glass: on the nature of near-infrared luminescence**Presented at the 7th Russian Workshop on Fibre Lasers, Novosibirsk, 5–9 September 2016.

This paper presents results of a detailed magneto-optical spectroscopy study of bismuth-doped aluminosilicate glass. At least three distinct optical centres are shown to coexist in the glass: bismuth ion clusters, Bi+ ions and defects in the glass structure, with energy transfer between the last two species. Analysis of magnetic circular dichroism and magnetic circular polarisation of luminescence as functions of magnetic field and temperature indicates that all three centres have an even number of electrons (holes). Experimental evidence is presented that both ‘red’ and near-infrared luminescence bands are due to transitions in the defects.

Near-infrared luminescence in TlCl:Bi crystal

Experimental and theoretical studies of spectral properties of crystalline TlCl:Bi are performed. Two broad near-infrared luminescence bands with a lifetime of about 0.25 ms are observed: a strong band near 1.18 μm excited by 0.40, 0.45, 0.70, and 0.80 μm radiation and a weak band at ≳1.5 μm excited by 0.40 and 0.45 μm radiation. Computer modeling of Bi-related centers in TlCl lattice suggests that a Bi(+)…VCl(Cl)(-) center (Bi(+) in Tl site and a negatively charged Cl vacancy in the nearest anion site) is most likely responsible for the IR luminescence.

Magneto-optical studies of iron impurity in HVPE GaN

We report on optical studies of bulk GaN crystals doped with iron. High-quality freestanding GaN crystals with varying Fermi level position were grown using the hydride vapor phase epitaxy on bulk GaN substrates. Samples with the dominant neutral Fe 3+(3d 5) acceptor state showed a characteristic near-infrared luminescence band around 1.3 eV, consisting of several sharp lines due to the fine structure of the 4T 1(G)– 6A 1(S) internal transitions of isolated Fe 3+(d 5) ions. In a magnetic field, these lines split into several components. This allowed us to determine energy structure of the 4T 1 multiplet in the magnetic field. For samples containing a singly ionized Fe 2+(3d 6) acceptor, absorption due to well-resolved 5E– 5T 2 internal transitions of Fe 2+ was observed. Measurements performed at different temperatures ranging from 7 to 50 K and at magnetic fields up to 13 T enabled us to analyze some sublevels of the 5E ground and the 5T 2 excited state.

Photoluminescence Characteristics of TiO2and Their Relationship to the Photoassisted Reaction of Water/Methanol Mixture

This work investigated the photoluminescence characteristics of TiO2 and discussed the relationship between the photoluminescence features of TiO2 and the photoassisted reaction of water/methanol mixture. It is found that anatase TiO2 displays a visible luminescence band centered at about 505 nm and rutile TiO2 mainly shows a near-infrared luminescence band centered at about 835 nm, which are respectively ascribed to the oxygen vacancies in anatase TiO2 and the intrinsic defects in rutile TiO2. The visible luminescence band is easily quenched by the Pt deposited on the surface of TiO2, while the near-infrared luminescence band is hardly influenced by the deposited Pt. It is suggested that the excited electrons trapped in the oxygen vacancies of anatase are facilely transferred to Pt to contribute to the photoassisted reaction, but the electrons trapped in the intrinsic defects of rutile are not.

Luminescent CdTe nanocrystals as ion probes and pH sensors in aqueous solutions

CdTe nanocrystals capped by short-chain thiol molecules can easily be prepared in aqueous solution, possess a single narrow emission band and can potentially be used as luminescence sensors and ions probes. We report the effect of pH and various ions, including physiology important cations such as calcium(II), manganese(II) and iron(III), on the luminescence intensity of CdTe nanocrystals capped by thioglycolic acid. Quenching of luminescence of CdTe nanocrystals by Ag(I)-cations points out their use in cellular studies as fluorescent labels and quenching agents, respectively. Micromolar amounts of Hg 2+ ions caused quenching of the emission of CdTe nanocrystals, while at increasing Hg 2+ concentration alloyed Cd x Hg 1− x Te nanocrystals were formed, followed by appearance of a near-infrared luminescence band. Luminescence of both bare CdTe nanocrystals and CdTe nanocrystals embedded into polymer microcapsules was found to be pH sensitive within the pH range of 4–6.

Electroluminescence mechanism in SiOx layers containing radiative centers

Luminescent silicon oxides containing radiative centers were obtained by using two different techniques. Silicon rich silicon oxides (SRSOs) were fabricated by rf magnetron sputter deposition and Ge-implanted SiO2 films were fabricated by ion implantation following the thermal oxidation of Si. Blue and violet photoluminescence were observed from the SRSO and the Ge-implanted SiO2, respectively. However, the electroluminescence (EL) spectra from both oxides exhibited red and near-infrared luminescence bands. Strong EL was observed only under reverse bias conditions on metal-luminescent oxide–semiconductor structures. The EL intensity and peak position were varied with applied voltages. According to the EL and current–voltage measurements, it is concluded that the possible EL mechanism is the impact ionization of ground state electrons in the radiative centers.

Photoluminescence and Zeeman effect in chromium-doped 4H and 6H SiC

Photoluminescence (PL) and Zeeman effect measurements in near-infrared luminescence bands in Cr-doped 4H and 6H SiC are presented. The PL spectrum consists of two no-phonon lines (NPLs) at 1.1583 and 1.1898 eV in 4H SiC and three NPLs at 1.1556, 1.1797, and 1.1886 eV in 6H SiC. The observed Zeeman splittings and temperature dependence studies reveal the spin triplet of the ground state and the orbital doublet structure of the excited state of the Cr-related center. All the triplets have almost isotropic g values close to 2 with trigonal symmetry and small zero-field splitting values D. In contrast, the effective g values of the excited state of the center are very anisotropic with g∥ in the range of 0.22–0.64 and g⊥=0 for different NPLs in both polytypes. Based on the Zeeman results, the PL is attributed to the internal transition 1E(D)→3A2(F) within the d shell of a substitutional, neutral chromium (Cr4+) in the 3d2 electronic configuration.

Luminescence of tungsten impurities in ZnSe

A new near-infrared luminescence band due to internal transitions of tungsten in ZnSe crystals is described. It is characterized by a weak zero-phonon line (ZPL) at ( nm) and 40 partially strong phonon satellites which reveal the presence of quasilocalized modes with energies of 33, 77, and . A magnetic field does not split the ground state, indicating that this is a state of a low-spin configuration of . The lifetime of the excited state is . Intense absorption bands around 12 000 and dominating the PLE spectrum are assigned to internal W transitions. Under excitation with ) a further emission appears starting at with a weak ZPL followed by several stronger phonon lines. The distances between these peaks coincide in some cases with the quasilocalized modes of the former emission. Therefore, this luminescence is probably also related to tungsten centres.

Near-Infrared Luminescence Spectroscopy of Nickelocene Doped into Single Crystals of Ruthenocene

Single crystals of ruthenocene doped with nickelocene show a near-infrared luminescence band with a maximum at 13 100 cm(-1) and a width of 1100 cm(-1) at 5 K in addition to the ruthenocene luminescence. The band is symmetric and attributed to nickelocene on the basis of a comparison of luminescence and absorption spectra. Energy transfer from the ruthenocene host enhances the nickelocene luminescence intensity at temperatures between 50 and 100 K. An activation barrier of 306(18) cm(-1) is determined from luminescence decay measurements. The Stokes shift of 2200 cm(-1) and the large change of 0.16 Å in nickel-cyclopentadienyl distance in the emitting state confirm the assignment as (3)E(1g), arising from an electron configuration different from that of the ground state. The comparison of experimental and calculated spectra shows that only low-energy vibrational modes contribute to the luminescence band shape, in contrast to the case of cobaltocene doped in the same host lattice, where a distortion along a high-frequency, ligand-centered mode affects the luminescence band shape.

Identification of the 1.19-eV luminescence in hexagonal GaN.

We report on optical investigations of a near-infrared luminescence band in hexagonal GaN with a single zero-phonon line (ZPL) at 1.1934 eV. It is attributed to the spin-forbidden internal d-d transition $^{1}$E(D)${\mathrm{\ensuremath{-}}}^{3}$${\mathit{A}}_{2}$(F) of a defect with a ${\mathit{d}}^{2}$ electronic configuration. This assignment is based on the observed Zeeman splittings, which agree with the ground and excited states being threefold and twofold degenerate, respectively. This interpretation is supported by the observed small full width at half maximum (FWHM) of the ZPL, the weak phonon sideband, and the weak temperature dependence of the luminescence band. With increasing temperature, the ZPL shifts towards lower energies but maintains its FWHM of about 200 \ensuremath{\mu}eV up to 60 K. The observed luminescence lifetime of 65 \ensuremath{\mu}s indicates a strong mixing of the $^{1}$E(D) with the $^{3}$${\mathit{T}}_{2}$(F) multiplet at slightly higher energies by spin-orbit interaction. Photoluminescence excitation spectra show intracenter absorption into the higher excited $^{3}$${\mathit{T}}_{1}$ states at 1.62 and 2.8 eV in n-type samples, proving the defect to be in the luminescent charge state in n-type material. Thus, we propose ${\mathrm{Ti}}^{2+}$ as the luminescence center responsible for the 1.19-eV transition. Implications for the band offset between GaN and GaAs are discussed.

Sensitized near-infrared luminescence from cobaltocene doped in single crystals of ruthenocene

Single crystals of ruthenocene doped with cobaltocene show a broad near-infrared luminescence band at 750 nm (13 400 cm-1) in addition to ruthenocene luminescence. This new band is attributed to cobaltocene by comparison with the absorption spectrum. The intensity of this band increases with temperature, a manifestation of thermally activated energy transfer between the metallocene molecules.

Empirical one-electron model of optical transitions in Cu-doped ZnS and CdS

Optical absorption and emission processes in the paradigmatic wide-gap II-VI compounds ZnS: Cu and CdS: Cu find an unconstrained interpretation in a plain strong-field model of light-induced electronic processes which depicts the charge states Cu2+ (d9) and Cu+ (d10), viz. their internal and charge transfer transitions. A variety of observed spectroscopic features between the UV and the IR regions are included, supplemented by some tentative assignments and/or predictions. Among the phenomena covered are the blue (B-Cu), green (G-Cu) and orange-red (R-Cu) emission bands of ZnS and their homologues in CdS. Novel near-infrared luminescence bands in ZnS peaking near 7200 and 9200 cm-1 are tentatively assigned to radiative hole-recombination at a Cu acceptor state and to the t52e3 → t42e4 internal transitions of Cu3+ (d8), respectively. Participation of a native donor turns out to be essential for some of the processes covered. Formation of deep-acceptor-bound excitons is demonstrated for several absorptive and emissive optical transitions.