Vibronic Luminescence Research Articles

Manipulation of Temperature-Dependent Luminescence Behaviors of Mn4+-Activated Fluoride Phosphors.

In this paper, the giant tunability of thermal behaviors, i.e., from thermal deterioration to substantial growth, is firmly demonstrated for the vibronic luminescence of Mn4+ ions in fluoride phosphors. Such peculiar behavior is uncovered to be associated with the thermal excitation of a low-frequency phonon bath, and a theoretical model involving the excitation-wavelength-dependent populations of vibronic levels and the temperature-dependent nonradiative recombination processes is successfully constructed. Two main governing parameters, namely, the thermal activation energy Ea and the involved average phonon energy ΔE, are thus determined for the distinct thermal behaviors of Mn4+-ion luminescence. This demonstration may pave the way for manipulating the thermal behaviors of vibronic luminescence in solids to some extent.

Luminescent Pt(II) Complexes Containing (1-Aza-15-crown-5)dithiocarbamate and (1-Aza-18-crown-6)dithiocarbamate: Mechanochromic and Solvent-Induced Luminescence.

The strong tendency to stack in the solid state and rich luminescence for the Pt(II) complexes makes them potential candidates as new mechanochromic materials and sensing applications. Six mononuclear complexes [Pt(ppy)(O4NCS2)] (1), [Pt(bpy)(O4NCS2)]ClO4 (2), [Pt(ppy)(O5NCS2)] (3), [Pt(phen)(O4NCS2)]ClO4·CH3OH (5a), [Pt(phen)(O4NCS2)]ClO4 (5b), and [Pt(phen)(O5NCS2)]ClO4 (6a), one dinuclear complex [Pt2(phen)2(NaO5NCS2)2(ClO4)3]ClO4 (6b), and one one-dimensional (1-D) coordination polymer {[Pt2(bpy)2(NaO5NCS2)2(ClO4)2](ClO4)2}n (4) were synthesized by reacting [Pt(ppy)Cl]2, Pt(bpy)Cl2, and Pt(phen)Cl2 (ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline) with (1-aza-15-crown-5)dithiocarbamate (O4NCS2) or (1-aza-18-crown-6)dithiocarbamate (O5NCS2), respectively, which have been isolated and structurally characterized by X-ray diffraction. Neutral complexes 1 and 3 contain no intermolecular Pt(II)···Pt(II) contact, whereas cationic complexes 2, 5a, 5b, and 6a with ClO4- as counteranions show alternative intermolecular Pt(II)···Pt(II) contacts of 3.535/4.091, 3.480/5.001, 3.527/4.571, and 3.446/4.987 Å in the solid state, respectively. Interestingly, complex 4 forms a 1-D coordination polymer through coordination between the encapsulated Na+ ions inside the azacrown ether rings of O5NCS2 and ClO4- anions with respective intra- and intermolecular Pt(II)···Pt(II) contacts of 3.402 and 3.847 Å in crystal lattices, whereas a dinuclear complex 6b was surprisingly formed and also connected by the encapsulated Na+ ions and ClO4- anions with alternative intra- and intermolecular Pt(II)···Pt(II) contacts of 3.650 and 3.677/4.4.372 Å, respectively. Upon excitation, complexes 1 and 3 showed similar vibronic luminescence at 507, 534, and 502, 532 nm, respectively, and the other complexes 2 and 4-6 showed broad luminescence with maxima at 537-567 nm. The B3LYP/LanL2DZ calculation was carried out and used to clarify their excited-state properties. In addition, the powder samples for complexes 1-4 almost showed no energy shift for the luminescence and significantly those of complexes 5-6 exhibited the mechanochromic luminescence upon grinding. It is noted that complexes 5a and 6a only showed minor red shifts (i.e., from 544 to 556 nm for complex 5a and from 551 to 565 nm for complex 6a), whereas complex 6b exhibited a remarkable red shift from 558 to 603 nm upon grinding. Besides, their luminescence reversibility was also examined toward various solvents.

Luminescence behaviour of a Yb sensitized Er:YAG transparent ceramic prepared by the solid-state reaction method

Optical-grade yttrium aluminum garnet (YAG) ceramics co-doped with Yb3+ and Er3+ ions are successfully prepared via using high-temperature solid-state reaction method under vacuum condition. Cubic phase structure and full dense microstructure are determined by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) methods. Both characteristics endow our ceramic with high optical transmittance of ~82% at 600 nm. Moreover, the ceramic luminescent properties are mainly discussed with Yb3+ ions serving as an efficient sensitizer for Er3+ active centers. Both zero-phonon lines (ZPLs) and sidebands of Er3+ ions in the YAG ceramics are first analyzed and the most interesting finding of this work is the anti-Stokes sidebands showing remarkably stronger emission intensity than Stokes ones. This obtained result reveals the predominance of absorbing phonon energy in vibronic luminescence process under the weak crystal field.

New Lamellar Silver Thiolate Coordination Polymers with Tunable Photoluminescence Energies by Metal Substitution

The structures of two lamellar silver thiolate coordination polymers [Ag( p-SPhCO2H)] n (1) and [Ag( p-SPhCO2Me)] n (2) are described for the first time. Their inorganic part is composed of distorted Ag3S3 honeycomb networks separated by noninterpenetrated thiolate ligands. The main difference between the two compounds arises from dimeric hydrogen bonds present for the carboxylic acids. Indepth photophysical studies show that the silver thiolates exhibit multiemission properties, implying luminescence thermochromism. More interestingly, the synthesis of a heterometallic lamellar compound, [Ag0.85Cu0.15( p-SPhCO2H)] n (3), allows to obtain mixed metal thiolate coordination polymers and to tune the photophysical properties with the excitation wavelengths from a green vibronic luminescence to a single red emission band.

Photoluminescence and ultra-fast decay profiles of rare-earth (III) ion-doped semiconductor nanocrystals encapsulated in silica nanotube AMCM-41/Cd xZn 1− xS: Eu 3+, Tb 3+

Luminescence, time-resolved luminescence and decay profiles are measured in order to investigate quantum-confinement effects in alumina(Al 2O 3)-modified MCM-41 silica nanotubes doped with Zn x Cd 1− x S:Eu 3+, Tb 3+ nanocrystals at temperatures down to 10 K. In comparison with bulk materials, in the presence of vibronic luminescence bands, luminescence spectral characteristics are found associated with SiO 2 centers, a new f–f transition mechanism and very short (600 ps) lifetime features due to surface-bound centers.

Standardless Analysis of Multicomponent Mixtures of Substances by Time-Resolved Vibronic Spectroscopy

A new approach to the quantitative and qualitative standardless analysis of complex substances based on experimental time-dependent vibronic luminescence spectra (in the UV and visible regions) is proposed. The approach requires no preliminary calculation of absolute intensities for molecular models. It is shown that this analysis can be carried out for both individual substances and multicomponent mixtures, including unknown substances and mixtures of unknown composition. The concentration ranges of mixture components available for the analysis are evaluated, depending on the optical properties of mixtures.

Formation of S 2− and Se 2− molecular ions through photochemical reactions and their vibronic luminescence in KCl : MnS/Se crystals

It is found that when quenched KCl : MnS/Se crystals are irradiated with UV light, S 2 − and Se 2 − molecular ions are formed. By this method these molecular ions were effectively introduced into KCl lattice for the first time. At 8.8 K, such luminescence spectra consist of one or more vibronic series of zero-phonon lines associated with isotope structure and phonon-side bands. The spectroscopic constants ν 00, ω 0″ and ω 0″ x 0″ were calculated for the ground state of Se 2 − ions. On the other hand, from the detailed observation of photochemical reactions in KCl : MnS, it was found that Mn +, Mn 0 and F centers were produced following the formation of S 2 −. From above results, a model for the formation of S 2 − was proposed.

Observation of new vibronic luminescence band in semiconducting diamond

Steady state and time-resolved photoluminescence studies have been carried out for a new vibronic emission band, with a zero phonon line at 2.395eV, that is observed in type IIb semiconducting diamond. This band exhibits a relatively slow (228ns) photoluminescence decay that is exponential, and is believed to be due to an internal transition at a defect site.

Molecular Luminescence from Electron-Bombarded YBa2Cu3O7-x

Luminescence from electron-bombarded YBa2Cu3O7-x was investigated. It has been found that the luminescence is similar in shape and energy position to the vibronic luminescence due to the CN- molecule, indicating that the luminescence is attributed to the CN- adsorbed on the YBa2Cu3O7-x surface but not to the luminescence of intrinsic origin.

The segregation of nickel-related optical centres in the octahedral growth sectors of synthetic diamond

Abstract The vibronic absorption bands with zero-phonon lines at 1·40, 1·883, and 2·51 eV, the broad absorption band with a maximum near 1·4eV and the series of absorption lines near 3·1 eV, the vibronic luminescence bands with zero-phonon lines at 1·40eV and 2·56 eV, all associated with nickel-related optical centres in synthetic diamond, are shown in this investigation to be restricted exclusively to the octahedral growth sectors. In addition, absorption in a sharp line at the Raman frequency (1332cm−1), at the high-frequency limit of the defect-induced one-phonon region, is present only in the octahedral sectors. The relative intensities of the different absorption bands depend on the nitrogen concentration in the diamond. The 1·883 and 2·51 eV systems are strongest in samples containing a high nitrogen concentration, whereas the 1·4 eV broad band and 1·40 eV vibronic system are strongest in diamonds with a low nitrogen concentration.

Exciton Dynamics in β-9,10-Dichloroanthracene

Flaky crystals of β-dichloroanthracene are grown by sublimation method. Polarized absorption and luminescence spectra have been examined over the temperature range from 300 K to 6 K. The lowest singlet exciton absorption band is confirmed to be located at 23370±20 cm -1 at 6.5 K. The exciton-phonon coupling strength is estimated to be 1.66. Vibronic luminescence bands have been observed at temperatures below 37 K and above 180 K and are assigned as due to radiative annihilation of free excitons. Adiabatic potential energy curves are proposed to explain those luminescence spectra and the parameters are obtained as follows: The self-trap depth=-1400±200 cm -1 . The half-width of the free exciton band=2100±300 cm -1 . The self-trapping barrier height=75±5 cm -1 . Possibility of the presence of two kinds of self-trapped exciton states is briefly discussed.

Multiphoton excitation of Mn 4+ and Cr 3+ luminescence in MgO

Multiphoton excitation of the luminescence spectra of Mn 4+ and Cr 3+ ions has been observed in single crystal MgO. MgO crystals irradiated with pulses from a XeCl laser exhibit a strong 745 nm luminescence band at 293 K. The 670.6 nm vibronic luminescence band of Mn 4+ was readily observable at 14 K. The luminescence of the 670.6 nm line shows a six photon dependence on incident XeCl laser intensity, suggesting that the 670.6 nm emission is pumped by energy transfer from excitonioy molecules. Cr 3+ emission also shows a multiphoton dependence on excitation intensity.

Cathodoluminescence studies of carbon-13 diamond

Vibronic luminescence bands associated with seven point defects have been studied for synthetic diamonds grown using 99% C-13. Changes in the electronic and vibrational energies have been compared with those expected theoretically.

Frenkel Exciton Dynamics in Anthracene under High Pressure and Quasi-Free Exciton State

The polarized absorption and luminescence spectra of anthracene crystals have been investigated under high pressures and at room temperature. A satellite absorption band which shifts to lower energy with increasing pressure is found to be related with the vibronic luminescence series. As the origin of the vibronic luminescence a model of a quasi-free exciton is proposed. The vibronic luminescence bands loose their intensity with pressure and are replaced by intrinsic self-trapped exciton luminescence at pressures higher than about 18 kbar. Self-trapping of excitons seems to be enhanced by the second order phase transition which occurs at 24 kbar. The exciton-phonon coupling constant at 22 kbar is estimated to be at least 1.6 which should be compared to 0.85 at ambient pressure.

Vibronic spectra of Eu3+ in lanthanide oxysulfides and oxyhalides

Vibronic luminescence spectra and vibronic luminescence-excitation spectra with laser excitation were considered in this work. At low temperatures the luminescence spectra of Eu/sup 3 +/ and Tb/sup 3 +/ in oxysulfides and oxyhalides contain hundreds of lines. The vibronic side bands of the electronic transitions are isolated with the aid of the temperature dependence of the intensity of the lines. The vibronic excitation spectra were also considered, making it possible to get rid of some of the superpositions and to obtain the single-phonon bands in a ''purer'' form and at lower temperatures. The temperature dependence of the intensities of lines has been used to identify the vibronic bands in the luminescence spectra of Eu/sup 3 +/ and Tb/sup 3 +/ in lanthanide oxysulfides and of Eu/sup 3 +/ in these compounds have been obtained. A comparison of the vibronic spectra with the IR and Raman spectra has been carried out, and the width of the phonon bands has been evaluated. Graphs and tables are included.