Quenching Activation Energy Research Articles

Enhanced red emissions and higher quenching temperature based on the intervalence charge transfer in Pr3+ doped LiNbO3 with Mg2+ incorporation

For investigating the effect of exceeding Mg2+ doping on optical properties and luminescent mechanism, detailed spectroscopic characterizations of Pr3+ (1 mol%) and Mg2+ (0 and 5mol%) doped congruent LiNbO3 (CLN) single crystals were studied. The exceeding Mg2+ doping of 5mol% was found to enhance the dominant red emissions (1D2→3H4) under 360nm excitation with a larger population of 1D2 via the Pr3+-Nb5+ intervalence charge transfer (IVCT). Quenching of blue-green emissions in Pr3+ doped CLNs was ascribed to the depopulation of 3P0 via IVCT state. The lifetimes related to 1D2→3H4 were significantly increased with Mg2+ incorporation at a temperature range from 20K to 430K. As the temperature rises, the progressively thermal quenching of the red emission and lifetime was observed, which was interpreted with the thermally activated energy transfer from the IVCT state to ground level 3H4. More importantly, exceeding Mg2+ doping led to a displacement of the IVCT state in the configuration coordinate diagram, resulting in larger quenching activation energy and higher quenching temperature (310K→370K) in Pr:Mg:CLN. The emission enhancement and quenching temperature increase at exceeding Mg2+ concentration were considered to be of practical value in luminescent and laser applications.

Multichannel luminescence properties and ultrahigh-sensitive optical temperature sensing of mixed-valent Eu2+/Eu3+ co-activated Ca8ZrMg(PO4)6(SiO4) phosphors

A novel dual-emitting Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors with ultrahigh-sensitive optical temperature sensing are prepared by a conventional solid-state method. The Eu2+/Eu3+ co-activated Ca8ZrMg(PO4)6(SiO4) phosphors exhibit efficient dual-mode emissions with an intense, broad blue emission peaked at 414 nm and a relative bright red-emitting centered at 614 nm under 297 nm UV-light excitation, respectively. Furthermore, the fluorescence intensity ratio (FIR) technology is applied to analyse the optical temperature sensing performance of Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors. Based on different thermal quenching behavior of Eu2+ and Eu3+ dual-emitting centers, linear temperature-dependent FIR between Eu2+ and Eu3+ is obtained. The maximal absolute sensitivity reaches as high as 5.94% K−1, which is superior to that for the other luminescent temperature sensing materials reported previously. Analyses of the temperature-dependent photoluminescence spectra and configurational coordinate diagrams for Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors indicate that the temperature-sensitive variation in FIR of Eu2+ to Eu3+ is originated from the difference in thermal quenching activation energy for 5d→4f transition of Eu2+ and 5D0→7FJ (J = 1, 2, 4) transitions of Eu3+. These results reveal that the Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors show glorious potential in high temperature optical thermometry.

Structural, electrical, and photoluminescence properties of Pr3+ doped Na0.25K0.25Bi2.5Nb2O9 bismuth layer-structure ceramics

In this paper, Pr3+ doped Na0.25K0.25Bi2.5Nb2O9 (NKBN-xPr3+) ceramics were successfully prepared via a conventional solid-state reaction process. The structural, dielectric, and piezoelectric properties as well as photoluminescence performance of the samples were systemically studied. All the ceramic samples possessed a pure two-layered bismuth layer-structure with the A2 1 am space group. Raman spectra revealed that the doped Pr3+ ions mainly replaced Bi3+ at the A-sites in the pseudo-perovskite layers. With increasing Pr3+ concentration, the Curie temperature and the maximum dielectric constant of the samples decreased, while the piezoelectric constant d 33 increased from 15 pC/N for x = 0 to 21 pC/N for x = 0.01. Addition, d 33 remained almost unchanged for all samples when the annealing temperature was lower than 450 °C. Under excitation with 452 nm light, the obtained samples exhibited a typical emission of Pr3+ ions, with the strongest red emission peak centered at 609 nm. The corresponding color tone of the ceramics shifted from red-orange to orange-yellow with increasing Pr3+ doping. The thermal quenching behavior of the photoluminescence of the x = 0.01 sample was also investigated in detail, and the thermal quenching activation energy was calculated to be 0.4473 eV. Our study indicated that NKBN-xPr3+ ceramics may have potential applications in multi-functional devices.

Influence of silver nanoparticles on relaxation processes and efficiency of dipole – dipole energy transfer between dye molecules in polymethylmethacrylate films

The fluorescence and phosphorescence of dyes in thin polymethylmethacrylate (PMMA) films in the presence of ablated silver nanoparticles has been investigated in a wide temperature range by methods of femtosecond and picosecond laser photoexcitation. The fluorescence and phosphorescence times, as well as spectral and kinetic characteristics of rhodamine 6G (R6G) molecules in PMMA films are measured in a temperature range of . The temperature quenching activation energy of the fluorescence of R6G molecules in the presence of ablated silver nanoparticles is found. The vibrational relaxation rate of R6G in PMMA films is estimated, the efficiency of the dipole – dipole electron energy transfer between R6G and brilliant green molecules (enhanced by plasmonic interaction with ablated silver nanoparticles) is analysed, and the constants of this energy transfer are determined.

Thermal quenching in calcite and evaluation of quenching parameters from composite glow curve by a computerized resolved peak technique

Thermoluminescence (TL) glow curves of X-ray irradiated micro-grain calcite mineral were recorded at various heating rates (2, 4, 6, 8 and 10K/s) under same linear temperature profile from 300 to 520K. By using a Computerized Glow Curve Deconvolution technique, all composite glow curves of calcite were analyzed and the glow curves were found to be a combination of three distinct overlapping peaks. Activation energies corresponding to these three peaks were found to be 0.70, 0.60 and 1.30eV respectively. For each set of computerized resolved peak, variation of peak maximum temperature, FWHM and peak area with heating rate were studied. Entire glow curves were found to be influenced by thermal quenching. Thermal quenching activation energy, W and the pre-exponential unitless constant, C were evaluated from each resolved peak individually. Thermal quenching activation energies for the three peaks were found to be 1.36±0.54, 1.14±0.73 and 1.38±0.40eV respectively. The significance of determining the individual value of quenching parameters related to each peak for a composite glow curve is reported.

Luminescent properties of sol–gel processed red-emitting phosphor Eu3+, Bi3+ co-doped (Ca,Sr)(Mo,W)O4

A series of red-emitting phosphors Ca0.6Sr0.4−1.5y−1.5zMo1−xWxO4:EuyBiz (x = 0–1, y = 0–0.14, z = 0–0.12) have been synthesized by a sol–gel method. The effects of calcining temperature, concentrations of Bi3+ and Eu3+, and the W/Mo ratio on the luminescent properties were investigated. X-ray diffraction and scanning electron microscopic results showed that as-prepared phosphors were of single phase with several microns. The Bi3+ and Eu3+ co-doped phosphors showed remarkably intense red emission at 618 nm. The emission intensities of the series reached maximum for compositions at x = 0.4, y = 0.12 and z = 0.08 when the calcining temperature was 900 °C. Temperature dependent emission intensity of the phosphor suggested that the as-synthesized product had good thermal stability with a thermal quenching activation energy of 0.31 eV. The decay curves showed the energy transfer efficiency from MoO42− to Eu3+ increased with an increase in the Mo6+ doping content.

Low temperature studies of the photoluminescence from colloidal CdSe nanocrystals prepared by the hot injection method in liquid paraffin

This article describes the results from low temperature studies of the photoluminescence (PL) from colloidal CdSe nanocrystals prepared by the hot injection method in liquid paraffin. The synthesized nanocrystals were taken from the reaction mixture at different time intervals, their sizes were all within the quantum confinement range, and showed the typical size-dependent UV–vis absorption, PL and Raman spectral characteristics. The PL spectra and their temperature dependences were measured from room temperature (295K) down to temperatures as low as 15K, demonstrating that the exciton PL transitions followed the Varshni equation. The thermal quenching activation energy below 100K was relatively low, while the luminescence was strongly quenched as the temperature was increased above 100K, probably pointing at change in the degree of carrier localization. The smallest (2.6nm in size) CdSe nanocrystals isolated in the beginning of the nanocrystal growth had a relatively symmetric size distribution and showed a single exciton emission band, while the samples isolated at later stages of the growth process showed negatively skewed asymmetric size distribution, indicating that the growth mechanism of nanocrystals could be explained by the model of Ostwald ripening. The obtained results are expected to be helpful for better understanding of the PL properties of quantum dots and their formation and growth in non-polar organic solvents.

Reduction of thermal quenching of biotite mineral due to annealing

Abstract Thermoluminescence (TL) of X-ray irradiated natural biotite annealed at 473, 573, 673 and 773 K were studied within 290–480 K at various linear heating rates (2, 4, 6, 8 and 10 K/s). A Computerized Glow Curve Deconvolution technique was used to study various TL parameters. Thermal quenching was found to be very high for un-annealed sample, however it decreased significantly with increase in annealing temperature. For un-annealed sample thermal quenching activation energy (W) and pre-exponential frequency factor (C) were found to be W = (2.71 ± 0.05) eV and C = (2.38 ± 0.05) × 1012 s−1 respectively. However for 773 K annealed sample, these parameters were found to be W = (0.63 ± 0.03) eV, C = (1.75 ± 0.27) × 1014 s−1. Due to annealing, the initially present trap level at depth 1.04 eV was vanished and a new shallow trap state was generated at depth of 0.78 eV which contributes very low thermally quenched TL signal.

Study on the spectroscopic properties of Pb2+ doped SrI2 single crystals

Optical transmission and absorption, radioluminescence, temperature-dependent photoluminescence and fluorescence time profiles of Pb2+ doped SrI2 crystals were investigated. The optical absorption spectrum presents characteristic absorption bands corresponding to the 6S2–6S6P transitions of Pb2+ ions and an undetermined absorption band peaking at 435nm. Radioluminescence at the room temperature displays a broad emission band in 400–800nm range with absorption dip at 420–450nm. Three distinct emissions with different luminescence mechanisms and behaviors are observed within the 80–300K range. Under the 378nm excitations, Pb2+ doped SrI2 crystal presents an intense, asymmetric, and broad emission corresponding to the 3P0,1→1S0 transitions. The thermally active phonon assistant tunneling from the excited states of the lower energy emission (3P0→1S0) to the excited states of the higher energy emission (3P1→1S0) is suggested to be responsible for the observed spectral blue-shift with the rising temperature. The thermal quenching activation energy is calculated as 0.50±0.04eV for the 3P1→1S0 transition. Under the 433nm excitation, emission bands peaking at 510nm and 680nm are observed. The 510nm emission shows double exponential decay characteristic with decay times varying in ns range, and its intensity gradually reduces with the rising temperature. Radiative transition processes predominate the symmetric 680nm emission, which thus shows weak thermal quenching.

Thermoluminescence characteristics of X-ray induced kyanite mineral and its thermal quenching parameters

Thermoluminescence (TL) glow curves of X-ray irradiated micro-grain natural kyanite have been recorded under annealed and un-annealed condition at various heating rates (2, 4, 6, 8 and 10 K s−1). TL parameters such as activation energy, order of kinetic and pre-exponential frequency factor have been investigated from the glow peak by a computerized glow curve deconvolution technique. Variation of peak integrals, peak maximum temperatures, FWHM and activation energy with heating rates have been investigated and the glow curves at higher rates have been found to be influenced by presence of thermal quenching. For annealed sample value of thermal quenching activation energy (W) and pre-exponential factor (C) are found to be 0.86 ± 0.02 eV and 2.5 × 109 s−1 respectively and for un-annealed sample these values are 1.68 ± 0.03 eV and 3.1 × 1010 s−1 respectively. Experimentally measured value of W and C have been verified by estimating thermal quenching efficiencies η(T) with the help of calculated value of W and C; quenched glow curves have been successfully reconstructed for each heating rate. The dose sensitivity of both types of samples is also reported. Annealed sample shows improved dose response than un-annealed sample.

Thermoluminescence study of X-ray irradiated muscovite mineral under various heating rate

The thermoluminescence (TL) glow curves of X-ray irradiated micro-grain natural muscovite were recorded within 298–520K at various linear heating rates (2K/s, 4K/s, 6K/s, 8K/s and 10K/s). Natural TL of muscovite was checked, but no significant TL was observed within 298–520K in any heating rate. Within the heating rate 2–10K/s only a low temperature distinct peak was observed in the temperature range 348–357K. The TL parameters such as activation energy, order of kinetic, geometrical symmetry factor and pre-exponential frequency factor were investigated from the glow peak by Peak Shape (PS) method and Computerized Glow Curve Deconvolution (CGCD) technique. At lowest heating rate the glow peak obeys non-first order kinetic and at the highest heating rate it follows the second order kinetic. The variation of peak integrals, peak maximum temperatures, FWHM and activation energy with heating rates were investigated, and the glow curves at higher rates were found to be influenced by the presence of the thermal quenching. The thermal quenching activation energy and pre-exponential factor were calculated and found to be 2.31±0.02eV and 3.46×1014s−1, respectively.

Thickness dependence of temperature-induced emission mechanism in InGaN/AlGaN short-period superlattices

An analysis of temperature-dependent photoluminescence (PL) spectra for a series of InGaN/AlGaN short-period superlattices (SP-SLs) with different well and barrier thickness is presented. A quantitative model, based on Gaussian-like function of localized electronic states, to fit the temperature-dependent emission peak energy gives good fits over an extended temperature range for all samples. It is found that, among all parameters in the model, the degree of broadening of the Gaussian distribution is strongly dependent of the structural parameters of SP-SLs and determines the anomalous “S-shape” behavior of the temperature-dependent emission energy. In thin well and barrier samples with higher broadening parameter, the temperature-dependence of emission energy is different from those of typical “S-shape” behavior, which is characterized by the bigger red-shift with no blue shift in the temperature range used. The depth of localization, Ea-Eo, is smaller than the corresponding activation energy obtained from the thermal quenching of the PL intensity, thus, indicating that the thermal quenching activation energy and the localization due to band-gap fluctuation most likely have different origins. We demonstrate that, in the InGaN/AlGaN SP-SLs, the interface characteristics also contributes to the temperature-induced PL emission shift as much as the compositional fluctuation does.

Luminescence properties of a new greenish blue emitting phosphor Na5Ca4(PO4)4F:Eu2+

A novel greenish blue emitting phosphor, Na5Ca4(PO4)4F:Eu2+, was synthesized by a conventional solid-state reaction, and its phase formation was confirmed by using the X-ray powder diffraction (XRD) technique. The photoluminescence (PL) results showed that the phosphor could be efficiently excited by ultraviolet (UV) light at wavelength of 250–410nm, and it exhibited bright greenish blue emission under 365nm UV light. The emission spectrum showed a single broad band centered at 500nm, corresponding to the 4f65d1→4f7 transition of Eu2+. Eu2+ concentration dependent PL properties in Na5Ca4(PO4)4F:xEu2+ indicated that there was a dipole–dipole interaction of Eu2+ ions. The critical energy-transfer distance was around 19.8Å. Furthermore, this phosphor had good thermal stability and its thermal quenching activation energy was 0.45eV. The measured quantum efficiency of Na5Ca4(PO4)4F:0.01Eu2+ phosphor under 365nm excitation is 76%, which means that the present phosphor is promising in the white light emitting diodes (LEDs) phosphors.

Investigating the luminescence properties as a function of activator concentration in single crystal cerium doped Lu2SiO5: Determination of the configuration coordinate model

The effect of cerium concentration on single crystal lutetium orthosilicate (Lu2SiO5, LSO) was investigated with temperature-dependent steady state and time resolved luminescence spectroscopy. The results were used to determine the thermal quenching activation energies and the phonon energies responsible for the thermal broadening of the luminescence spectra. The measured phonon values were used to calculate configuration coordinate (CC) diagrams of the luminescence centers. The nature of single crystal LSO:Ce concentration quenching was determined to be due to radiative energy transfer by self-absorption. The observed broadening of the excitation spectra and narrowing of the emission spectra with increasing cerium was explained via a CC model. A combination of the CC model and concentration quenching explained the measured thermal quenching activation energies.

Dose and dose rate dependence of time-resolved OSL from Korean paleosol quartz

Abstract Using a newly developed small X-ray irradiator equipped with a mini X-ray generator (Varian VF-50J) and TR-OSL measurement system attached to an MCS (ORTEC MCS-PCI), the influence of dose and dose rate of X-ray radiation on TR-OSL was investigated in paleosol quartz from the Chungdang-dong paleolithic site, Korea. All lifetimes were calculated by a curve-fitting method using a single stretched-exponential function with β = 0.86. Physical characteristics, natural lifetime, thermal quenching activation energy ΔE, and thermal assistance activation energy Ea were firstly determined. From the results of the investigation of dependence on dose and dose rate of X-ray radiation using fully bleached samples, the lifetime decreased significantly to about 20 μs; when the X-ray dose was increased to 300 Gy at a dose rate of 0.5 Gy/s. Also, despite different radiation dose rates, at a dose of 50 Gy both lifetime and related intensity were independent of dose rate change.

Investigation of photoluminescence mechanisms of ZnO through experimental and first-principles calculation methods

The photoluminescence properties of ZnO were investigated experimentally and by a first-principles method. Thermal treatment of ZnO in various atmospheres provides insight into the ultraviolet (UV) and green emission mechanisms. These mechanisms were investigated in detail from the thermal quenching behavior of the emission spectra of ZnO. The negative thermal quenching of the green emission could be fitted exactly with a model equation based on the assumption that UV emission loss by thermal quenching affects green emission. The electronic states of ZnO clusters with and without an oxygen vacancy were calculated by first-principles calculations using the discrete variational (DV) Xα molecular orbital method. This method gave a reasonably accurate calculation of band-gap energy. The energy levels calculated by the DV-Xα method agree well with experimentally measured thermal quenching activation energy and the zero-phonon energy of green emission. The results indicate that oxygen vacancies function as luminescent centers for green emission.

Temperature dependence of localized exciton transitions in AlGaN ternary alloy epitaxial layers

The optical properties of Ga-rich AlxGa1−xN (x=0.019, 0.038, 0.057, 0.077, and 0.092) ternary alloy epitaxial layers have been studied by means of temperature-dependent photoluminescence (PL) and time-resolved PL spectroscopy. The luminescence intensity of excitons in five epitaxial layers indicated a thermal quenching process with two activation energies. The two quenching activation energies were attributed to the delocalization of excitons and thermal dissociation of excitons. Anomalous temperature dependence of the PL peak energy was also observed in the epitaxial layers, which enabled the evaluation of the localization energy of the excitons. The localization energy increased as the 1.7th power of the PL linewidth, which reflected a broadening of the density of localized exciton states. In addition, the luminescence decay of the localized excitons for the five epitaxial layers became longer with decreasing emission energy. These observations suggest that the decay of excitons is caused not only by radiative recombination, but also by transfer to lower energy states.

Photoinduced Energy Transfer in Poly(trimethylene terephthalate)

Photoinduced energy transfer in poly(trimethylene terephthalate) (PTT) was investigated by examining its excitation wavelength and concentration dependences of fluorescence in solutions. Accordingly, critical quench concentration and critical trap formation concentration were identified. Besides, studies of temperature effect on photoluminescence (PL) behavior of amorphous PTT film from −183 to +177 °C revealed that both fluorescence and phosphorescence emissions at low temperature can be attributed to monomers and traps. Phosphorescence quenching originated from the discontinuous increase of nonradiative processes. The corresponding quenching activation energies were estimated to be 13.5 kJ/mol for monomer phosphorescence quenching and 17.2 kJ/mol for exciplex phosphorescence quenching, respectively. Furthermore, the PL method proved to be able to monitor molecular relaxations (including γ-, β-, and α-transitions) and cold crystallization in PTT film, which used to be measured by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), respectively.

Quenching of Singlet Molecular Oxygen (1O2) by Azide Anion in Solvent Mixtures¶

The azide ion is a strong physical quencher of singlet molecular oxygen (1O2) and is frequently employed to show involvement of 1O2 in oxidation processes. Rate constants (kq) for the quenching of 1O2 by azide are routinely used as standards to calculate kq values for quenching by other substrates. We have measured kq for azide in solvent mixtures containing deuterium oxide (D2O), acetonitrile (MeCN), 1,4-dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1O2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1O2. In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. kq was 4.78 × 108M−1 s−1 in D2O and increased to 26.7 × 108 and 27.7 × 108M−1 s−1 in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D2O mixtures, kq decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol−1 in D2O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from kq values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown kq values.

Structural and Optical Properties of Self-assembled InAs Quantum Dots as a Function of Rapid Thermal Annealing Temperature

We present the effects of rapid thermal annealing (RTA) temperature on the structural and optical properties of self-assembled InAs quantum dot (QD) structures grown on GaAs substrates by molecular beam epitaxy (MBE). The photoluminescence (PL) measurements are performed in a closed-cycle refrigerator as a function of temperature for the unannealed and annealed samples. RTA at higher temperature results in the increase in island size, the corresponding decrease in the density of islands, and the redshift in the PL emission from the islands. The temperature dependence of the PL peak energy for the InAs QDs is well expressed by the Varshni equation. The thermal quenching activation energies for the samples unannealed and annealed at <TEX>$600^{\circ}C$</TEX> are found to be <TEX>$25{\pm}5meV$</TEX> and <TEX>$47{\pm}5$</TEX> meV, respectively.