Room Temperature Absorption Research Articles

Spectroscopic studies of KGd(WO 4) 2:Ho 3+ single crystals

Single crystals of KGd(WO 4) 2 doped with Ho 3+ ions were grown by the top seeded solution growth method. Polarized room temperature absorption spectra were analyzed by means of the conventional Judd–Ofelt theory taking into account strong dependence of the host refractive index on the wavelength. In addition to the intensity parameters Ω 2, Ω 4, Ω 6, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. The transitions predicted by the phenomenological model as potential transitions for laser applications are discussed. Emission spectra in the green, red, and near-infrared spectral regions were recorded for different excitation wavelengths. Comparison with spectroscopic properties of Ho 3+ ion in other crystals is discussed.

Room temperature absorption in laterally biased quantum infrared detectors fabricated by MBE regrowth

In this paper, we show room temperature operation of a quantum well infrared photodetector (QWIP) using lateral conduction through ohmic contacts deposited at both sides of two n-doped quantum wells. To reduce the dark current due to direct conduction in the wells, we apply an electric field between the quantum wells and two pinch-off Schottky gates, in a fashion similar to a field effect device. Since the normal incidence absorption is strongly reduced in intersubband transitions in quantum wells, we first analyze the response of a detector based on quantum dots (QD). This QD device shows photocurrent signal up to 150K when it is processed in conventional vertical detector. However, it is possible to observe room temperature signal when it is processed in a lateral structure. Finally, the room temperature photoresponse of the QWIP is demonstrated, and compared with theory. An excellent agreement between the estimated and measured characteristics of the device is found.

Yb,Na:PbF_2: a potential new high-power laser material

Yb:PbF(2) and Yb,Na:PbF(2) laser crystals are grown by the Bridgman method. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes of Yb(3+) ions in the crystals have been investigated. Experimental results show that Na(+) ions codoping with Yb(3+) as charge compensators can suppress the deoxidization of Yb(3+) to Yb(2+). The result of diode-pumped laser operation of a Yb,Na:PbF(2) single crystal is reported for the first time to the best of our knowledge . With a 1mol.%Yb(3+)-doped sample, we obtained 2.37W output power at 1056nm for 17.9W of incident power at 978nm.

The synthesis, X‐ray structure analysis, and photophysical characterization of 4‐[(E)‐2‐(4‐cyanophenyl)diazenyl]‐morpholine

Abstract A novel triazene, 4‐[(E)‐2‐(4‐cyanophenyl)diazenyl]‐morpholine (1) was prepared via a diazonium ion coupling reaction between 4‐aminobenzonitrile and morpholine. The x‐ray structure of 1 was determined and evidenced π delocalization in the triazene subunit. The room temperature absorption spectrum of 1 in acetonitrile was dominated by an intense triazene‐centered π→π* transition at 325 nm. Compound 1 was observed to be luminescent, with an emission maximum at 434 nm in room temperature acetonitrile solution. The emission spectrum of 1 in propionitrile glass at 77K exhibited a narrowed emission band with a maximum at 449 nm. Broad emission from 400–700 nm with poorly resolved vibrational structure was observed from solid 1 at room temperature. J. Heterocyclic Chem., 2011.

ChemInform Abstract: A Flash Photolysis Investigation of the Gas Phase UV Absorption Spectrum and Self-Reaction Kinetics of the Neopentylperoxy Radical

The ultraviolet absorption spectrum of the neopentylperoxy radical, (CH 3 ) 3 CCH 2 O 2 (or C 5 H 11 O 2 ), and the kinetics of its self-reaction have been studied in the gas phase using a flash photolysis technique. The room temperature absorption cross-section at 250 nm was determined to be σC 5 H 11 O 2 (250 nm)=(5.18±0.78)×10 −18 cm 2 molecule −1 and was used to normalize the radical absorption spectrum between 210 and 300 nm. Detailed modeling of the self-reaction system was used to interpret the transient absorption kinetic decay curves over the temperature range 228-380 K, at total pressures between 25 and 100 torr. The results are discussed in relation to previous measurements of alkylperoxy radical spectra and kinetics

Synthesis, structure and optical studies of inorganic–organic hybrid semiconductor, NH 3(CH 2) 12NH 3PbI 4

Synthesis, crystal structure and optical properties of two-dimensional layered inorganic–organic hybrid NH 3(CH 2) 12NH 3PbI 4 are presented. Intercalation strategy has also been used to fabricate single crystal and thin films of the same. As thin film, they are well oriented and stacked along the [l 0 0] direction with strong room-temperature excitonic absorption and emission characteristics. Exciton features were correlated with the relative inorganic network crumpling and conformation of alkylammonium chains. The structural features are compared with those of similar hybrid, (H(CH 2) 12NH 3) 2PbI 4.

Crystal growth and spectroscopic studies of novel Yb-doped K5Nd(MoO4)4 single crystals

K5Nd(MoO4)4 crystals with different Yb3+ concentrations were grown using Czochralski technique. Room-temperature absorption spectra were recorded and assigned on the basis of Dieke's diagram for Nd3+ ion; the standard Judd–Ofelt theory has been used to analyze the spectra. Increase of Yb3+ concentration leads to variation of the corresponding Judd–Ofelt intensity parameters. Significant contribution of the Yb↔Nd energy transfer into the formation of the Nd3+ absorption spectra causes the observed changes. After illumination of the crystals with CW Nd:YAG laser changes of the birefringence for the laser line of CW He–Ne laser at 633nm were studied. Birefringence changes show good correlation with the content of Yb ions.

Interaction of oxovanadium(IV) with tricarboxylic ligands in aqueous solution: A thermodynamic and spectroscopic study

In this paper we report an investigation on coordination compounds of vanadyl ion with citric, D(+)- threo-isocitric, cis- and trans-aconitic acids in aqueous solution. The different binary systems have been studied by potentiometric and spectroscopic techniques ( t = 25 °C, I = 0.1 mol dm −3). Electronic paramagnetic resonance spectroscopy (EPR) at room temperature and molecular absorption spectrophotometry were employed in order to obtain a structural characterization of complexes. A speciation model was proposed for all the metal–ligand systems from potentiometric data. For all the systems studied the chemical model assumes the formation of complexes with stoichiometry MLH r and binuclear species M 2L 1H − r . Citric and D(+)- threo-isocitric acids also form stable dimeric species M 2L 2H − r . The EPR investigation reveals that the dimeric complexes of hydroxyacids present magnetic interaction supporting the hypothesis of an alcoholate-bridged dinuclear structure. For each system investigated we recorded visible absorption spectra and estimated the individual spectrum of species in solution. A particular spectrophotometric behaviour of citrate system was recognized and the joint examination of our spectroscopic results and the literature data leads us to suppose that the trans position of vanadyl is occupied by the bridged alcoholate group.

Influence of deposition conditions on nanocrystalline InN layers synthesized on Si(1 1 1) and GaN templates by RF sputtering

We present a detailed investigation on the influence of deposition conditions on morphological, structural and optical properties of InN films deposited on Si(1 1 1) and GaN-on-sapphire templates by reactive radio-frequency (RF) sputtering. The deposition parameters under study are nitrogen content in the sputtering gas, substrate–target distance, substrate temperature and RF power. X-ray diffraction measurements confirm the (0 0 0 1) preferred growth orientation and the wurtzite crystallographic structure of the material. For optimized deposition conditions, InN on Si(1 1 1) substrates presents smooth surface with root-mean-square roughness ∼1 nm. Surface quality of the InN films can be further improved by deposition on GaN-on-sapphire templates, achieving root-mean-square roughness as low as ∼0.4 nm, comparable to that of the underlying substrate. The room-temperature absorption edge is located at 1.70 eV. Intense low-temperature photoluminescence peaking at 1.60 eV is observed.

The Synthesis, Photophysical Characterization, and X‐Ray Structure Analysis of Two Polymorphs of 4,4′‐Diacetylstilbene

AbstractA palladium(II) acetate‐catalyzed synthesis of 1 that utilizes the novel triazene 1‐{4‐[(E)‐morpholin‐4‐yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption spectra of 1 in various solvents exhibited a π→π* transition in the range of 330–350 nm. Compound 1 was observed to be luminescent, with room‐temperature solution and solid‐state emission spectra that exhibited maxima in the range 400–500 nm. All room‐temperature absorption and emission spectra exhibited some degree of vibrational structure. The emission spectrum of 1 at 77 K in propanenitrile glass was broad and featureless with a maximum at 447 nm. Compound 1 crystallized as a yellow and colorless polymorph. X‐Ray structure analyses of both of these polymorphs and 1‐{4‐[(E)‐morpholin‐4‐yldiazenyl]phenyl}ethanone are presented.

Statistical average of model orbital potentials for extended systems: Calculation of the optical absorption spectrum of liquid water

Time-dependent density functional theory (TD-DFT) calculations of the electronic response of molecular and bulk liquid water based on a very accurate orbital-dependent ground-state exchange-correlation potential, the statistical average of (model) orbital potentials (SAOP), and on the adiabatic local density approximation (ALDA) for the exchange-correlation kernel are described. The quality of the calculated excitation energies, both in the molecule and in the liquid, is assessed by comparison to hybrid TD-DFT calculations and experimental data. A combination of classical molecular dynamics simulations and TD-DFT calculations sampling several disordered configurations of a small liquid sample is then used to simulate the optical absorption spectrum in the region of 0–15 eV. The resulting room-temperature absorption profile is discussed in connection with previous TD-DFT calculations as well as with results from Green’s function theory and experiment.

Efficient Light Harvesting by Photosystem II Requires an Optimized Protein Packing Density in Grana Thylakoids

A recently developed technique for dilution of the naturally high protein packing density in isolated grana membranes was applied to study the dependence of the light harvesting efficiency of photosystem (PS) II on macromolecular crowding. Slight dilution of the protein packing from 80% area fraction to the value found in intact grana thylakoids (70%) leads to an improved functionality of PSII (increased antenna size, enhanced connectivity between reaction centers). Further dilution induces a functional disconnection of light-harvesting complex (LHC) II from PSII. It is concluded that efficient light harvesting by PSII requires an optimal protein packing density in grana membranes that is close to 70%. We hypothesize that the decreased efficiency in overcrowded isolated grana thylakoids is caused by excited state quenching in LHCII, which has previously been correlated with neoxanthin distortion. Resonance Raman spectroscopy confirms this increase in neoxanthin distortion in overcrowded grana as compared with intact thylakoids. Furthermore, analysis of the changes in the antenna size in highly diluted membranes indicates a lipid-induced dissociation of up to two trimeric LHCII from PSII, leaving one trimer connected. This observation supports a hierarchy of LHCII-binding sites on PSII.

Spectroscopic properties of Pr 3+:Gd 3Ga 5O 12 crystal

The room-temperature absorption spectrum, fluorescence spectra, and fluorescence decay curves of Pr 3+-doped Gd 3Ga 5O 12 single crystal were studied systematically. The standard and modified Judd–Ofelt theories were used to determine the Judd–Ofelt intensity parameters Ω t ( t = 2, 4, 6), radiative transition probabilities, radiative lifetimes and branching ratios. The stimulated emission cross-sections and the fluorescence quantum efficiency of the promising laser levels were calculated and discussed. The multi-exponential behavior of the fluorescence decay curve of the 1D 2 → 3H 4 transition was explained by using the Inokuti–Hirayama theory. The obtained spectroscopic results show the potential application of the Pr 3+-doped Gd 3Ga 5O 12 crystal as visible solid-state lasers.

Infrared laboratory absorbance spectra of olivine: using classical dispersion analysis to extract peak parameters

Laboratory measurements quantifying the effect of Fe substituting for Mg in olivine are needed to distinguish compositional from temperature, grain size and grain shape effects in observational data. To address this need, we study room temperature absorption spectra of a large suite of olivines evenly spaced across Mg and Fe compositions. We apply the principle that classical dispersion theory may be used to determine peak positions as well as peak widths, strengths and possibly optical function (n(λ) and k(λ)) estimates from absorption spectra of thin film samples of these olivines and two additional isotropic and anisotropic minerals with varying hardness and numbers of spectral bands. For olivine, we find that this method provides good estimates of peak position and that accounting for asymmetric peak shapes in this way increases the error on full width at half-maximum and oscillator strengths. Values from classical dispersion fits better match published n and k derived from reflectivity of single crystals when the dust proxy is soft and the thickness of the sample is independently constrained. Electronic data and peak parameter trends for the laboratory olivine absorption spectra and the viability of the extracted n and k are discussed with regard to astronomy.

Excited State Distortion in Photochromic Ruthenium Sulfoxide Complexes

A series of photochromic ruthenium sulfoxide complexes of the form [Ru(bpy)(2)(OSOR)](+), where bpy is 2,2'-bipyridine and OSOR is 2-(benzylsulfinyl)benzoate (OSOBn), 2-(napthalen-2-yl-methylsulfinyl)-benzoate (OSONap), or 2-(pentafluorophenylmethanesulfinyl)benzoate (OSOBnF(5)), have been synthesized and characterized. In aggregate, the data are consistent with phototriggered isomerization of the sulfoxide from S-bonded to O-bonded. The S-bonded complexes feature (3)MLCT absorption maxima at 388 nm (R = BnF(5)), 396 nm (R = Bn), and 400 nm (R = Nap). Upon charge transfer excitation the S-bonded peak diminishes concomitant with new peaks growing in at approximately 350 and approximately 495 nm. Spectroscopic and electrochemical data suggest that the electronic character of the substituent on the sulfur affects the properties of the S-bonded complexes, but not the O-bonded complexes. The isomerization is reversible in methanol solutions and, in the absence of light, thermally reverts to the S-bonded isomer with biexponential kinetics. The quantum yields of isomerization (Phi(s-->o)) were found to be 0.32, 0.22, and 0.16 for the R = BnF(5), Bn, and Nap complexes, respectively. Kinetic analyses of femtosecond transient absorption data were consistent with a nonadiabatic mechanism in which isomerization occurs from a thermally relaxed (3)MLCT state of S-bonded (or eta(2)-sulfoxide) character directly to the singlet O-bonded ground state. The time constants of isomerization (tau(s-->o)) were found to be 84, 291, and 427 ps for the R = BnF(5), Bn, and Nap complexes, respectively. Analysis of room temperature absorption and 77 K emission spectra reveal significant distortion between the S-bonded ground state ((1)GS(S)) and singlet metal-to-ligand charge transfer state ((1)MLCT(S)) and thermally relaxed (3)MLCT, respectively. The distortion is primarily attributed to low frequency metal-ligand and S horizontal lineO vibrational modes, which are intrinsically involved in the isomerization pathway.

Crystal structure and optical study of Tm:Sc2SiO5 single crystal

Sc 2 SiO 5 : 4 at . % Tm crystal was obtained by the Czochralski method and the crystal cell parameters were calculated. Sixfold coordinated Sc-ions occupied two different crystallographic sites but the low temperature optical spectra only represented energy transitions originating from Tm ions residing in one site. Room temperature absorption spectrum was analyzed in the framework of Judd–Ofelt theory and the calculated absorption coefficient and cross section were 10.47 cm−1 and 5.55×10−21 cm2 at 791 nm respectively. Stimulated emission cross sections for the F34–H36 transition near 1900 nm were evaluated using the reciprocity method while the luminescence F34 lifetime was measured to be 1.14 ms. We conclude that Tm:Sc2SiO5 is promising for diode-pumped infrared lasers.

Synthesis, Morphology, and Optical Characterization of Nanocrystalline Er3+:Y2O3

We describe a methodology to synthesize trivalent-erbium (Er3+)-doped yttrium oxide (Y2O3) nanoparticles. An in-depth morphology analysis indicates that the average diameter of the individual nanoparticles is about 25 nm. To optically characterize the nanocrystalline material, the room-temperature absorption spectrum has been obtained between 400 and 900 nm. The spectrum consists of six absorption bands, including 2G(1)9/2, 4F3/2 + 4F5/2, 4F7/2, 2H(2)11/2 + 4S3/2, 4F9/2, and 4I9/2. The room-temperature fluorescence spectra of the Er3+ (4f11) 2H(2)11/2 + 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions were analyzed for the crystal-field splitting of the energy levels of these states of erbium. We have measured the lifetimes for the 2H(2)11/2 + 4S3/2 and 4F9/2 metastable states and have investigated the effects of Er3+ concentrations and particle size on the emission intensity and decay times. The experimental energies (Stark levels) agree well within the experimental error with the theoretical values reported earlier for bulk single crystalline Er3+:Y2O3. Detailed structural and optical analyses suggest that the nanoparticles of Er3+:Y2O3 have potential applications in diverse fields of photonics including laser systems and optical communication devices.

Spectroscopic properties of new luminescent system based on vanadate(V) crystal doped with erbium ions

Er 3+-doped KCaY(VO 4) 2 microcrystalline samples were synthesized using a high temperature solid-state reaction technique. Spectroscopic properties of Er 3+: KCaY(VO 4) 2 are studied and the nature of emissions is discussed. A strong green and infrared luminescence were observed under excitation at 314 nm in the O 2−→V 5+ charge-transfer transitions and direct excitation of Er 3+ ions at 435 nm. A strong emission lines in the blue region are due to the transitions of VO 4 3− ions have been observed at 77 K. The Judd–Ofelt parametrization scheme has been applied to the analysis of the room temperature absorption spectra in order to evaluate the intensity parameters, the branching ratios and the radiative lifetimes of the 4I 13/2, 4I 11/2, 4F 9/2 and 4S 3/2 emitting levels. The effective cross-section has been calculated for the 4I 13/2→ 4I 15/2 transition, indicating that the title compounds is a promising active medium for application in the three-level laser system. The up-conversion emission in Er 3+: KCaY(VO 4) 2 was investigated at 300 K. The decay profiles of the Stokes and anti-Stokes emissions were measured and the mechanism of up-conversion luminescence is discussed.

Spectroscopic studies of Nd 3+ and Er 3+ in KGd(WO 4) 2 single crystals

Single crystals of KGd(WO 4) 2 doped with Nd 3+ and Er 3+ ions were grown by the top seeded solution growth method. Detailed analysis of the room-temperature absorption spectra was performed using the conventional Judd–Ofelt theory and actual dependence of the refractive index on the wavelength. In addition to the intensity parameters Ω 2, Ω 4, Ω 6, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. Those transitions which can be potentially used for laser applications have been identified for both ions.

Crystal growth and Judd–Ofelt analysis of novel Yb-doped RbNd(WO 4) 2 single crystals

RbNd(WO 4) 2 single crystals with different concentrations of Yb 3+ have been grown using the top seeded solution growth. Room-temperature absorption spectra were assigned on the basis of the Dieke's diagram for Nd 3+ ion and analyzed by means of the standard Judd–Ofelt theory. It was shown that the increase of the Yb 3+ concentration and corresponding decrease of the Nd 3+ concentration leads to the increase of the corresponding Judd–Ofelt intensity parameters, which suggests significant contribution of the Yb–Nd energy transfer in the formation of the absorption spectra.