Photoluminescence Decay Profiles Research Articles

Effect of Sm3+ ions concentration on borosilicate glasses for reddish orange luminescent device applications

Zinc Bismuth Strontium Borosilicate (ZnBiSrBSi) glasses doped with varying concentrations of samarium (Sm3+) ions have been synthesized via melt quenching technique and characterized by using XRD, SEM, optical absorption, excitation, Photoluminescence (PL) and decay spectral measurements. The amorphous nature of the as prepared glass has been confirmed by XRD and SEM measurements. The PL spectra recorded for the as-prepared glasses under 403 nm excitation show four emission bands from 4G5/2 level to 6HJ (J = 5/2, 7/2, 9/2 and 11/2). Among the four emission transitions, 4G5/2 → 6H7/2 transition at 600 nm is having highest intensity. The intensity of PL spectra in the titled glasses increases with increase in Sm3+ ions concentration up to 0.5 mol% and beyond decreases due to concentration quenching. Dexter theory applied to the emission spectral features reveals the energy transfer mechanism between Sm3+- Sm3+ ions as dipole-dipole in nature. The experimental lifetimes measured from the PL decay profiles for the intense 4G5/2 → 6H7/2 transition decreases with increase in Sm3+ ions concentration due to energy transfer between Sm3+-Sm3+ ions. All the aforementioned studies finally reveal that 0.5 mol% of Sm3+ ions in ZnBiSrBSi glasses is optimum in fabricating the reddish orange luminescent devices.

Integral Method Analysis of Electroabsorption Spectra and Electrophotoluminescence Study of (C4H9NH3)2Pbl4 Organic–Inorganic Quantum Well

Electric-field-induced changes in absorption and photoluminescence (PL) spectra and in PL decay profile have been measured for two-dimensional hybrid organic–inorganic halide perovskite semiconductor, ((C4H9NH3)2Pbl4) (N1). Electroabsorption (E-A) spectra observed at room temperature and at a low temperature of 45 K were analyzed by assuming the Stark shift, and the magnitudes of the change in electric dipole moment and polarizability following photoexcitation were determined. The strong signal observed in the E-A spectra at 45 K was interpreted in terms of the weak absorption band which shows extremely large Stark shift resulting from the large change in polarizability following photoexcitation. Electrophotoluminescence spectra of this compound, that is, field-induced change in PL spectra, show that PL of N1 is quenched by the application of electric field. Field effects on PL decay profiles show that the quenching results both from the field-induced decrease of the population of the emitting state follo...

Ultrafast endothermic transfer of non-radiative exciplex state to radiative excitons in polyfluorene random copolymer for blue electroluminescence

We report a blue-emitting random copolymer (termed modified Aryl-F8) consisting of three repeat units of polydioctylfluorene (F8), Aryl-polydioctylfluorene (Aryl-F8), and an aromatic amine comonomer unit, poly(bis-N,Ν′-(4-butylphenyl)-bis-N,N′-phenyl-1,4 phenylenediamine) chemically linked to get an improved charge carrier balance without compromising on the photoluminescence (PL) quantum yield with respect to the Aryl-F8 homo-polymer. The measured photoluminescence quantum efficiency (∼70%) of the blue-emitting polymer is comparable to or greater than the individual monomer units. The time resolved PL spectra from the modified Aryl-F8 are similar to those of Arylated-poly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4 phenylenediamine) (PFB) even at a time scale of 100–250 ps, indicating an ultrafast energy transfer from the (Aryl-F8 or F8):Arylated-PFB interface to Arylated-PFB, i.e., endothermic transfer of non-radiative exciplex to a radiative molecular exciton. Furthermore, the presence of non-radiative exciplex is confirmed by the photoluminescence decay profile and temperature dependent PL spectra. The luminance efficiency achieved for the modified Aryl-F8 polymer light-emitting diodes is ∼11 cd A−1 with an external quantum efficiency (EQE) of ∼4.5%, whereas it is 0.05 cd/A with an EQE of ∼0.025% for Aryl-F8. Almost two orders of higher efficiency is achieved due to the improved charge carrier balance from the random copolymer without compromising on the photoluminescence yield.

Inhomogeneous Photoluminescence Characteristic in Carbon Nanodots and Electrophotoluminescence Measurements

Photoluminescence (PL) spectra, time-resolved PL spectra, and PL decay profiles have been observed for carbon nanodots (CDs) with different excitation wavelengths in an embedded solid film and in s...

Characterizations of Pr-doped Yb3Al5O12 single crystals for scintillator applications

Yb3Al5O12 (YbAG) single crystals doped with different concentrations of Pr were synthesized by the Floating Zone (FZ) method. Then, we evaluated their basic optical and scintillation properties. All the samples showed photoluminescence (PL) with two emission bands appeared approximately 300–500 nm and 550–600 nm due to the charge transfer luminescence of Yb3+ and intrinsic luminescence of the garnet structure, respectively. A PL decay profile of each sample was approximated by a sum of two exponential decay functions, and the obtained decay times were 1 ns and 3–4 ns. In the scintillation spectra, we observed emission peaks in the ranges from 300 to 400 nm and from 450 to 550 nm for all the samples. The origins of these emissions were attributed to charge transfer luminescence of Yb3+ and intrinsic luminescence of the garnet structure, respectively. The scintillation decay times became longer with increasing the Pr concentrations. Among the present samples, the 0.1% Pr-doped sample showed the lowest scintillation afterglow level. In addition, pulse height spectrum of 5.5 MeV α-rays was demonstrated using the Pr-doped YbAG, and we confirmed that all the samples showed a full energy deposited peak. Above all, the 0.1% Pr-doped sample showed the highest light yield with a value of 14 ph/MeV under α-rays excitation.

Photoelectrochemical hydrogen production using CdS nanoparticles photodeposited onto Li-ion-inserted titania nanotube arrays

This study reports the synthesis of cadmium sulfide (CdS) nanoparticles on Li+-inserted TiO2 nanotube array (Li-TNA) to fabricate Li-TNA/CdS heterojunction electrodes for photoelectrochemical (PEC) hydrogen production under air mass (AM) 1.5 light and solar visible light (λ>420nm). For fabrication of the heterojunction, Li+ is rapidly inserted into TNA pre-grown on Ti foil, and CdS is then photodeposited onto the Li-TNA electrodes for varying deposition times. Surface analyses reveal that sub-100-nm polycrystalline CdS particles partly cover the Li-TNA (length: ∼800nm, pore diameter: ∼100nm), enabling the heterojunction to utilize AM 1.5 light as well as visible light. In aqueous solutions of sulfide and sulfite, the Li-TNA/CdS exhibits an incident photon-to-current efficiency (IPCE) of ∼20% (λ=420nm) while generating H2 at a Faradaic efficiency of ∼100%. This PEC performance is superior to that of TNA/CdS, which is attributed to the Li+-enhanced charge transfer at the TNA/CdS interface. Electrochemical impedance analysis shows that the charge-transfer resistance of the TNA is reduced by ∼60% by Li+ insertion. Time-resolved photoluminescence decay profiles further reveal that the charge transfer in Li-TNA is completed within 0.8ns, which is ∼33% faster than that in TNA. The sample surface is analyzed using scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscopy, and the PEC behavior of the samples is discussed in detail.

Influence of carrier localization at the core/shell interface on the temperature dependence of the Stokes shift and the photoluminescence decay time in CdTe/CdS type-II quantum dots

We have systematically investigated the temperature dependence of absorption, photoluminescence (PL), and PL decay profiles in CdTe-core and CdTe/CdS type-II quantum dots (QDs). In CdTe/CdS QDs, Stokes shifts and PL decay time become larger with an increase in temperature above 120 K, while those in CdTe-core QDs are almost independent of temperature. The unusual temperature dependence of Stokes shifts and PL decay time in CdTe/CdS QDs is understood by considering carrier localization at the core/shell interface at low temperatures and thermal-energy-assisted detrapping from localized-exciton to type-II exciton states at higher temperatures. Furthermore, a phenomenological rate-equation model is developed to explain the experimentally observed temperature-dependent PL decay time.

Spectroscopic and Photoluminescent Properties of Indium Zinc Oxide (IZO) and IZO/Ag/IZO Sandwiched Film

We report the ellipsometric and photoluminescence (PL) properties of Indium zinc oxide (IZO) films, which were grown by radio frequency sputtering under Ar and O2 atmospheres. IZO films grown under an O2 atmosphere (IZO (O2)) showed enhanced PL properties when compared to the films grown under an Ar atmosphere (IZO (Ar)), particularly with respect to the band-edge emission. The enhancement of band-edge emission can be attributed to the reduction in the non-emissive defect states related to oxygen vacancies, which were repaired by sputtering under O2 atmosphere, whereas the PL enhancement in green region is probably due to the formation of the different types of defects under the excess oxygen environment. This was also supported by the results of time-resolved PL measurements, where the band-edge emission of IZO (Ar) showed rapid decay with a 50 ps lifetime, which indicates the dominance of the relaxation pathway to underlying defect states. In contrast, the PL decay profiles of IZO (O2) for band-edge and emissive defect states showed moderate decay with time-constants of 2.3 ns and 5.7 ns, respectively. The exciton relaxation dynamics were sensitive to the presence and its kinds of defect states, which were controlled by the growth conditions.

Optical, scintillation and thermally stimulated luminescence properties of Ce-doped yttrium–aluminum–indium garnet

We have investigated the photoluminescence (PL), scintillation and thermally stimulated luminescence (TSL) properties of 1 mol % Ce-doped Y3(AlXIn1−X)5O12 (X = 0–1; Ce:YAING). These samples showed strong and broad PL emission by Ce3+ ion appeared in the spectral range from 480 to 620 nm. The PL decay profiles can be represented by a first-order exponential function with the decay time ranging 39–62 ns. Furthermore, the scintillation spectra showed similar features with those observed in PL. The scintillation decay time profiles were approximated by second or third order exponential decay functions, and we observed 26–61 ns component due to Ce3+ emission. The X-ray induced afterglow levels of Ce:YAING were worse than that of Ce:Y3Al5O12. The pulse height spectra of Ce:Y3(Al0.26In0.74)5O12 showed a clear photoabsorption peak, and that of the scintillation light yield was around 6,700 photons/MeV. In TSL glow curves, Ce:YAING show the glow peak at around 110 °C.

Stark Spectroscopy of Absorption and Emission of Indoline Sensitizers: A Correlation with the Performance of Photovoltaic Cells

Electric field effects on photoexcitation dynamics and electronic properties of highly efficient indoline sensitizers, DN488, D205, and DN182, embedded in PMMA films have been examined by using electroabsorption (E-A) and electrophotoluminescence (E-PL) spectroscopic techniques and time-resolved photoluminescence (PL) decay measurements in the presence of electric fields. Photovoltaic performances have been also measured for devices constructed using these sensitizers. Then, field-induced quenching of PL and field-induced change in PL decay profile were observed, and it was found that these field effects, which depend on the sensitizers investigated herein, are well correlated with the trend of power conversion efficiencies of the corresponding photovoltaic cells. Electric dipole moment and molecular polarizability of these sensitizers both in the ground state (S0) and in the excited state have been calculated at the level of B3LYP/6-31G(d), and the differences of these physical parameters between S0 and ...

Emission enhancement in indium zinc oxide(IZO)/Ag/IZO sandwiched structure due to surface plasmon resonance of thin Ag film

We report on a photoluminescence (PL) enhancement in IZO/Ag/IZO sandwiched structure via surface plasmonic effects of 14nm-thick Ag film. In the presence of Ag thin film, the 2–8-fold enhancement was observed for the broad PL around 2.34eV, which can be originated from defect states in amorphous IZO film. The results of time-resolved PL spectra suggested that the increase in radiative recombination rate, and the maximum Purcell factor of 19 was estimated from the analysis of the PL decay profiles. The comparison between the results of static- and dynamic-PL measurement suggests that the non-radiative process after the excitation of the surface plasmon of the silver film also affects the total efficiency of the emission enhancement.

Scintillation and optical properties of Ce-doped YAGG transparent ceramics

We investigated photoluminescence (PL) and scintillation properties of Ce3+-doped Y3Al2Ga3O12 (Ce:YAGG) transparent ceramics synthesized by vacuum sintering with different Ce3+ concentrations (mol.%) from 0.3% to 1% (0.3%Ce:YAGG, 0.5%Ce:YAGG, 0.8%Ce:YAGG and 1%Ce:YAGG). The samples were synthesized by the vacuum sintering technique. The obtained samples showed a very strong and broad PL emission by the 5d1-4f transition of Ce3+ in the wavelength range from 470 to 600 nm. The PL decay profiles were approximated by a single exponential decay function with the time constants of around 33–39 ns. Furthermore, the scintillation spectra induced by X-rays showed similar features with those observed in PL. The scintillation decay time profiles followed a second-order exponential decay function. The fast component group (ranged 35–42 ns) were dominantly contributed by the 5d1-4f transition of Ce3+. The pulse height spectra utilizing the latter emissions showed a clear photoabsorption peak. Among those samples tested, 0.5%Ce:YAGG sample showed the highest scintillation light yield of 21,400 ph/MeV under 137Cs γ-ray irradiation.

Interfacial Charge-Carrier Trapping in CH3NH3PbI3-Based Heterolayered Structures Revealed by Time-Resolved Photoluminescence Spectroscopy

The fast-decaying component of photoluminescence (PL) under very weak pulse photoexcitation is dominated by the rapid relaxation of the photoexcited carriers into a small number of carrier-trapping defect states. Here, we report the subnanosecond decay of the PL under excitation weaker than 1 nJ/cm(2) both in CH3NH3PbI3-based heterostructures and bare thin films. The trap-site density at the interface was evaluated on the basis of the fluence-dependent PL decay profiles. It was found that high-density defects determining the PL decay dynamics are formed near the interface between CH3NH3PbI3 and the hole-transporting Spiro-OMeTAD but not at the CH3NH3PbI3/TiO2 interface and the interior regions of CH3NH3PbI3 films. This finding can aid the fabrication of high-quality heterointerfaces, which are required improving the photoconversion efficiency of perovskite-based solar cells.

Photoluminescence of atomic layer deposited ZrO2:Dy3+ thin films

Atomic layer deposition based on alternate cycling of ZrCl4, Dy(thd)3 and H2O as precursors was applied for preparation of nanocrystalline ZrO2:Dy thin films. Photoluminescence (PL) properties of Dy3 + in the ZrO2 films were studied at several laser excitations. Substantial activation of Dy3 + PL required thermal treatment at 900 °C. As a result of annealing, thinner (~ 80 nm) films with higher Dy content retained relatively high amount of tetragonal phase and remained crack-free. In thicker (~ 140 nm) films, considerable amount of monoclinic phase was formed and a peculiar microscale cracking pattern was developed along with phase segregation. It is demonstrated that the crystal structure of ZrO2 significantly influences the Dy3 + emission spectrum and, at least for ZrO2-type matrices, Dy3 + is an excellent luminescent microprobe in comparison with micro-Raman scattering. A Förster-like PL decay profile allowed a conclusion that the self-quenching due to cross-relaxation between Dy3 + ions had a marked impact on emission intensity.

Variations in Decay Rate of Green Photoluminescence in ZnO under Above- and Below-Band-Gap Excitation

The mechanism of the commonly observed green photoluminescence (PL) emission in ZnO is still controversial and is being actively discussed. Herein, through comprehensive time-resolved and excitation-energy-dependent PL measurements on variously annealed ZnO samples, we show that the PL decay profile, which is well fitted to a triple-exponential function, depends not only on temperature but also on excitation energy. Under excitation with photons near the band-gap energy, the decay profile is governed by three decay components with decay times of ∼2, ∼10, and ∼50 μs. The contribution from the slower ∼10 and ∼50 μs decay components becomes dominant when the photoexcitation energy is ∼100 meV below the band-gap energy of bulk ZnO. It has also been revealed the highest green PL intensity is achieved under excitation of photons with energies ∼100 meV below the band-gap energy of bulk ZnO as well. These PL features are interpreted in terms of the formation of sub-band-gap states, band edge perturbation, and the...

Electric Field Effects on Photoluminescence of CdSe Nanoparticles in a PMMA Film

External electric field effects on spectra and decay of photoluminescence (PL) as well as on absorption spectra were measured for CdSe nanoparticles in a poly(methyl methacrylate) (PMMA) film. Electrophotoluminescence (E-PL) spectra as well as electroabsorption spectra show a remarkable Stark shift which depends on the particle size, indicating a large electric dipole moment in the first exciton state. The E-PL spectra also show that PL of CdSe is quenched by application of electric fields, and the magnitude of the field-induced quenching becomes larger with increasing size. The PL decay profiles observed in the absence and presence of electric field show that the field-induced quenching of PL mainly originates from the field-induced decrease in population of the emitting state prepared through the relaxation from the photoexcited state.

In Situ Optical and Structural Studies on Photoluminesence Quenching in CdSe/CdS/Au Heterostructures

We report here detailed in situ studies of nucleation and growth of Au on CdSe/CdS nanorods using synchrotron SAXS technique and time-resolved spectroscopy. We examine structural and optical properties of CdSe/CdS/Au heterostructures formed under UV illumination. We compare the results for CdSe/CdS/Au heterostructures with the results of control experiments on CdSe/CdS nanorods exposed to gold precursor under conditions when no such heterostructures are formed (no UV illumination). Our data indicate similar photoluminescence (PL) quenching and PL decay profiles in both types of samples. Via transient absorption and PL, we show that such behavior is consistent with rapid (faster than 3 ps) hole trapping by gold-sulfur sites at the surface of semiconductor nanoparticles. This dominant process was overlooked in previous end-point studies on semiconductor/metal heterostructures.

Numerical investigation of mid-infrared emission from Pr $$^{3+}$$ 3 + doped GeAsGaSe fibre

The experimentally obtained luminescence characteristics of a praseodymium (Pr\(^{3+})\) doped chalcogenide glass fiber are studied numerically using a rate equation approach. The numerical model includes both the radiative and non-radiative transition paths whilst it neglects the up-conversion processes. Photoluminescence spectra at mid-infrared wavelengths ranging from 3.5 to 6 \({\upmu }\)m were obtained by using two pump wavelengths: 1.55 and 1.94 \({\upmu }\)m. A good agreement between the experiment and theory is obtained for the photoluminescence decay profiles.

Time-resolved photoluminescence of silicon microstructures fabricated by femtosecond laser in air

Green photoluminescence (PL) from silicon microstructures fabricated by femtosecond laser in air was studied at different temperature by time-resolved spectroscopy. The PL decay profiles are well fitted by a stretched exponential function: I(t)=I(0)*exp[-(t/τ)β]. The dependence of the decay time constant τ and of the stretching index β on PL photon energy and on the temperature is investigated. A model of transport and recombination of the carriers is introduced as a possible explanation of the stretched exponential decay. The nonradiative recombination rate of the localized carriers, which is dependent on the carrier density and influenced by the trapping site density and the temperature, is deduced to be responsible for this kind of decay.

Thickness dependence of photoluminescence-decay profiles of exciton-exciton scattering in ZnO thin films

We have investigated the photoluminescence (PL) dynamics of ZnO thin films under intense excitation conditions using an optical-Kerr-gating method. The PL bands originating from exciton-exciton scattering (P emission) and biexciton (M emission) have been observed at 10 K. The ultrashort gating time of 0.6 ps has enabled us to obtain precise information of the temporal profiles of the peak energies and the intensities of the P- and M-PL bands. We have found that the decay time of the P emission becomes longer with increasing film thickness, while that of the M emission is independent of the film thickness. Although the decay time of the P emission is an increasing function of the film thickness, the relation is not in proportion, which is contrary to the predicted proportionality based on a simple model of photon-like polariton propagation.