Luminescence Kinetics Research Articles

Synthesis and Laser-Related Spectroscopy of Er:Y2O3 Optical Ceramics as a Gain Medium for In-Band-Pumped 1.6 µm Lasers

In this paper, Er:Y2O3 optical ceramics were fabricated and details of the synthesis were presented. The spectral–luminescent properties of Er3+:Y2O3 optical ceramics were investigated. The absorption and emission cross-section spectra were determined. The luminescence kinetics at near 1.6 µm was single exponential and the lifetime of erbium 4I13/2 energy level was determined. In the frame of the conventional Judd–Ofelt theory, the emission properties of the energy levels of erbium 4I13/2 and 4I11/2 involved in laser operation at near 1.6 µm were calculated. The gain coefficient curves for typical values of the relative population of the upper laser level 4I13/2 were presented. The composition and structure were studied using the SEM, XRD, FTIR spectroscopy, and X-ray computer tomography techniques.

Excited state trap in erbium doped borate glass

Erbium doped borate glass is widely used in luminescent materials, the luminescence dynamics of erbium doped borate glass is of great significance for optimizing and improving the luminous efficiency. The 2% molar ratio erbium doped borate glass was synthesized by the traditional melt quenching method, and annealed at 260 °C below the borate glass transition temperature. The thermal performance parameters of borate glass undoped and doped with Er3+ were measured by differential scanning calorimetry with 10 °C/min. The transient emission spectrum and decay kinetics curves were measured for the luminescence mechanism of erbium doped borate. Er3+ ions have different lifetime when emitted at 556 nm with different excitation wavelengths, the excited state trap may exist in erbium doped borate glass.

Luminescence of AlN:Eu ceramics: Properties and mechanisms

Luminescence processes of AlN:Eu ceramics, prepared by high temperature spark plasma sintering method, were studied basing on material spectral characterization by measuring of photoluminescence and excitation spectra at different fixed temperatures within a region from 10 K up to room temperature, together with measurement of luminescence kinetics. In this material the Eu2+ ion emission at 530 nm is dominant, besides, a weak Eu3+ ion emission also is observed at ∼600 nm. Two main spectral regions for excitation of Eu2+ emission are located around 360 nm and 260 nm. Analysis of the results obtained demonstrates a presence of two luminescence mechanisms, which are originating the 530 nm emission. It was found that the 530 nm emission caused by 360 nm excitation represents the intra-center mechanism of Eu2+ ion luminescence, whereas the 260 nm exciting light is causing the recombination luminescence. The mechanism of the tunneling recombination luminescence is proposed. Regarding to Eu3+ ions, an excitation line at 464 nm was found that together with the 614 nm emission represents the intra-center luminescence. The persistent luminescence caused by Eu ions in AlN lasting within a time scale of hours is revealed.

Luminescent properties of carbon quantum dots synthesized by microplasma method

The luminescent carbon quantum dots were synthesized by microplasma treatment of a glucose solution at atmospheric pressure at room temperature. The spectral and kinetic characteristics of synthesized quantum dots were studied by time-resolved confocal scanning luminescent microscopy and time-correlated single photon counting. The emission spectra are wide non-elementary bands. Their maxima were located at 476, 500, 547 and 580 nm at the wavelengths of the exciting radiation of 375, 405, 470 and 532 nm, respectively. Three exponential components with decay time constants of 0.65, 2.2, and 6.2 ns were detected in the luminescence kinetics. The presence of these components is due to the formation of three different types of luminescence centers at quantum dots with different probabilities of quantum transitions. Presumably, it may be related to the activation of quantum dots by various impurities or other defects formed luminescence centers. The concentration of quantum dots was controlled by changing the microplasma processing time of the glucose solution.

The origin of bright cyan persistent luminescence in Ca2SnO4:La3+

The origin of bright cyan persistent luminescence in La3+-doped Ca2SnO4 is investigated by optical and electron paramagnetic resonance spectroscopy methods. The incorporation of La3+ ions in the material stimulates the formation of Sn2+ emission centers and charge trap centers. After exposure of the material to UV radiation, charge transfer processes to the trap centers result in the creation of two types of paramagnetic defects. Both defects are spin 1/2 systems with rhombic symmetry g-factor values, which correspond to electron and hole centers respectively. The role of the identified defects in the optical processes of the material is evidenced by a correlation of defect decay and persistent luminescence kinetics. Due to appropriate activation energies of the defects, light emission of Sn2+ centers is efficient and long-lasting. In this article, optimal lanthanum ion content is determined, the identity of the defects is discussed and a model of persistent luminescence in Ca2SnO4:La3+ is proposed.

Sol-gel auto-combustion synthesis and luminescence properties of GdCaAl3O7: RE3+ (RE=Eu, Tb, Eu@Tb) phosphors for near-ultraviolet light-triggered indoor illumination

The color-tunable GdCaAl3O7: RE3+ (RE = Eu, Tb, Eu@Tb) phosphors were synthesized via an ultrafast sol-gel auto-combustion synthesis method. The X-ray diffraction patterns confirmed the forming of GdCaAl3O7 tetragonal phase, and the scanning electron microscopy images indicated that the obtained products presented honeycomb-like structure due to the gas releasing during the auto-combustion process. The luminescent properties, concentration quenching mechanism, energy transfer mechanism, luminescent dynamics, thermal stability and product practicability of GdCaAl3O7: RE3+ (RE = Tb, Eu, Eu@Tb) phosphors were investigated systematically. All the GdCaAl3O7: RE3+ products presented the characteristic emission of doped RE3+. Using GdCaAl3O7: 50% Tb3+@3.0% Eu3+ as yellow-emitting phosphors in combination with commercial BAM: Eu2+ blue-emitting phosphors and a NUV chip can successfully package a warm white LED device with high color rendering index (CRI, 86.3) and low correlated color temperature (CCT, 3348 K) that was very suitable for near-ultraviolet light-triggered indoor illumination.

Design of Ratiometric Dual‐Emitting Mechanoluminescence: Lanthanide/Transition‐Metal Combination Strategy

AbstractMechanoluminescence (ML) materials with the ability to convert mechanical stimulate into visible light signals have enabled visualized mechanics sensing. To this point, stress sensing based on ML color is preferred over that based on ML intensity in terms of both sensing reliability and visual sensitivity. In this work, a ratiometric dual‐emitting ML strategy to realize the stress‐sensitive ML color variation, where the Lanthanide/transition‐metal combination is adopted to build the dual‐activator ML system is proposed. The difference in electronic configuration between Lanthanide and transition‐metal ions leads to the significant discrepancy in the response of corresponding luminescence kinetics to the instantaneous change of local crystal field environment induced by stress, which plays a key role in the strategy. This strategy establishes a new general path for the design of novel ratiometric ML materials.

Upconversion luminescent nanoheater based on NaGd(MoO4)2: Yb3+/Tm3+ nanocrystals: Surfactant-free solvothermal synthesis, upconversion photoluminescence and photothermal conversion

Multifunctional upconversion luminescent nanoheaters are realized based on NaGd(MoO4)2:Yb3+/Tm3+ nanocrystals synthesized by surfactant-free solvothermal method. The structure, morphology and composition of the nanocrystals are analysed by XRD, SEM, EDS, TEM, HRTEM and SAED techniques. Under 980 nm irradiation, NaGd(MoO4)2:Yb3+/Tm3+ nanocrystals emit blue luminescence with emission peaks located in the blue and near-infrared spectral regions. The electronic transition processes for the upconversion luminescence are discussed based on the excitation power-dependent upconversion luminescence, luminescent dynamics and Yb3+/Tm3+ energy levels. The nanocrystals show efficient photothermal conversion after irradiated by 980 nm laser. The photothermal conversion slope efficiency for NaGd(MoO4)2:Yb3+/Tm3+ nanocrystals irradiated by 980 nm laser for 10 s duration is 17.43 °C/W for 10 mol% Yb3+ doping and 43.64 °C/W for 15 mol% Yb3+ doping. Multifunctional luminescent nanoheater NaGd(MoO4)2:Yb3+/Tm3+ nanocrystals exhibit both upconversion photoluminescence and photothermal conversion capabilities, and are promising candidates for temperature self-monitoring photothermal therapy or other biological applications.

Luminescence response of neodymium ions to phase transformations in yttria-based solid-solution nanopowders

Subject of study. In this paper, we describe the luminescence properties of nanopowders of composition (Nd0.008Y0.992)2O3, (Nd0.008Y0.992)2O3+6mol%ZrO2, and (Nd0.008Gd0.496Y0.496)2O3+5mol.%ZrO2 with various percentages of monoclinic and cubic phases. Method. Photoluminescence and pulsed cathodoluminescence spectra are recorded, followed by interpretation of the results obtained. Main results. In the process of studying the luminescence bands corresponding to the 4F3/2→4I9/2 and 4F3/2→4I11/2 energy transitions for neodymium ions in nanopowder crystalline lattices, we identify several spectroscopic and kinetic properties that can be used to identify the substances and determine the crystal phases present. We show that there is slight broadening of the spectral lines in the continuum base of the 4F3/2→4I11/2 manifold; the intensity level below which the bands merge into a continuum increases as the amount of structural disorder caused by the zirconium- and gadolinium-ion dopants in the Y2O3 increases. Practical significance. The distinctive features of the photoluminescence spectra and the kinetics of neodymium-ion luminescence in the 4F3/2→4I9/2 and 4F3/2→4I11/2 bands can be used for unique identification of the substances present and determination of the crystal phases thereof; this will be of practical interest in the development of high-bandwidth ceramic active elements.

Tuning the Photoluminescence Properties of β‐NaYF4:Yb,Er by Bi3+ Doping Strategy

AbstractThe low luminous efficiency of upconversion materials limits their practical applications in various fields. The present study focuses on the efficient upconversion enhancement of β‐NaYF4:Yb,Er induced by Bi3+ doping. The XRD and SEM results show that introducing Bi3+ into the matrix lattice changes the microstructure and particle size of the crystal. The photoluminescence spectra show that at 6% Bi3+ doping, the red and green emission intensities are enhanced by 12 and 8 times, respectively. The reason could be the lattice distortion caused by Bi3+ doping, breaking the partial forbidden transition of rare‐earth ions. The fluorescence lifetime measurement reveals that the Bi3+ doping changes the environment around erbium ions, affecting the energy level lifetime of erbium ions, explaining the luminescence dynamics law. The present study provides a facile route to achieve nano/microstructures with intense upconversion luminescence with potential applications in optoelectronic devices.

Effects of activated Sr 2+ ion content on strong blue‐emitting Ca 2 Sb 2 O 7 materials for high‐quality WLED devices

In this report, the luminescent performances of the self-host blue-emitting Ca2Sb2O7 materials were investigated in terms of the sintering temperature and the dopant Sr2+ ion content. The emission intensity was enhanced with an increase of the sintering temperature as well as the lattice parameters. After doping the Sr2+ ions (>1.2 mol%), the emission spectra of Ca2Sb2O7 materials would be redshifted. The blue-emitting color (Ca2Sb2O7) turned into greenish-blue (Sr2+@1.6 mol%) and green (Sr2+@2 mol%) colors in sequence. In light of these interesting findings, the crystal structure, elemental composition, morphology, thermal stability, luminescent dynamics, luminescent efficiency, etc were investigated and compared. Finally, the mini-white lighting-emitting diodes (WLEDs) based on the blue-emitting Ca2Sb2O7, greenish-blue-emitting Ca0.4Sr1.6Sb2O7, and green-emitting Sr2Sb2O7 phosphors were fabricated by mixing commercial phosphors (CP). Especially, the Ca2Sb2O7-CP-WLED and Sr2Sb2O7-CP-WLED devices exhibited a warm white light with good correlated color temperature (<3200 K) and excellent color-rendering index (>88). All the above results suggested that the self-host emitting materials of Sr2+ activated Ca2Sb2O7 with color-tunable properties could be very promising for solid-state lighting applications.

Sensitization of Mn2+ Luminescence by Eu2+: A Combined Study Using Optical Spectroscopy and Luminescence Dynamics Simulations.

Owing to the intriguing luminescent feature, Mn2+-doped materials have attracted a lot of attention. Unfortunately, their application potential is hampered by the parity-forbidden nature of Mn2+ 3d-3d transition, and the insufficient excitation light absorption is the main obstacle. Although the use of a sensitization strategy effectively addresses this issue, explicit knowledge of the sensitization mechanism is insufficient, severely limiting the improvement of Mn2+ luminescence performance in a wide range of materials. Herein, the sensitization of Mn2+ luminescence is investigated in Eu2+, Mn2+-codoped SrMgP2O7 which has the high luminescence efficiency upon UV excitation. The electronic transition properties of Eu2+ and Mn2+ are studied by VUV-UV-vis spectroscopy, and the sensitization mechanism is elucidated by luminescence dynamics simulations. Efforts are also made to evaluate the impact of temperature variation on the sensitization efficiency. Based on these discussions, the collaboration of high-efficiency Eu2+ → Mn2+ energy transfer via dipole-dipole interaction and suppression of Mn2+ luminescence loss results in the significant sensitization of Mn2+ luminescence in Eu2+, Mn2+-codoped materials, which are essentially associated with probable orbital hybridization and weak electron-vibration interaction, respectively. Current research provides a practical guideline for analyzing the luminescence sensitization effect in the donor-acceptor system, which facilitates the development of materials with unique optical features.

Features of the pulsed cathodoluminescence kinetics of neodymium ion in yttrium-aluminum garnet and yttria

The kinetics of pulsed cathodoluminescence of Nd3+ ions in single crystals, ceramics, and nanopowders of Nd3+ : Y3Al5O12 (Nd3+ : YAG) and Nd3+ : Y2O3 under excitation by a 2 ns electron beam with average electron energies of 130, 150, and 170 keV was studied. In this case, the luminescence of these substances occurs after the termination of the electron beam. In Nd3+ : YAG, there are optical transitions from the 2F25/2 level of the neodymium ion in the ultraviolet and visible regions of the spectrum, as well as from the 4F3/2 level in the near infrared region. In Nd3+ : Y2O3, there are not transitions from the 2F25/2 level of the neodymium ion, but infrared luminescence occurs from the 4F5/2 and 4F3/2 levels. The luminescence kinetics is characterized by rise and decay and it is described by the difference of two exponential functions. It is found that the characteristic luminescence decay times are the lifetimes of the 2F25/2, 4F5/2 and 4F3/2 emissive levels, and the rise time is determined by their pumping in recombination and relaxation processes. The rise mechanisms of pulsed cathodoluminescence are substantially different from the mechanisms of &amp;quot;phosphor ignition&amp;quot;, which occur during ionization and excitation of the phosphor by an external source. Keywords: pulsed cathodoluminescence, neodymium ion, yttrium-aluminum garnet, yttria, kinetics, rise time, decay time.

Luminescence of colloidal quantum points Ag-=SUB=-2-=/SUB=-S/SiO-=SUB=-2-=/SUB=-, decorated by small nanoparticles Au

Ten-fold increase in quantum yield of defect luminescence was found in area 750 nm with simultaneuous growth of its attenuation from 4 to 200 ns, caused by decoration of quantum point (QP) Ag 2 S/SiO 2 (5.0±1.5 nm) surface with nanoparticles (NP) Au (2.0±0.5 nm). Based on analysis of luminescence kinetics at 77 and 300 K the conclusion was drawn on non-specific manifestation of plasmon-exiton interaction caused by polarization effects from NP Au at properties of small traps that participate in generation of defect luminescence kinetics of QP Ag 2 S/SiO 2 . Keywords: IR luminescence; luminescence attenuation kinetics; quantum points, plasmon nanoparticles, plasmon-exiton interaction.

Dual role of oxygen-related defects in the luminescence kinetics of AlN:Mn2.

This study presents the impact of temperature and pressure on AlN:Mn2+ luminescence kinetics. Unusual behavior of Mn2+ optical properties during UV excitation is observed, where a strong afterglow luminescence of Mn2+ occurs even at low temperatures. When the temperature increases, the contribution of the afterglow luminescence is further enhanced, causing a significant increase in the luminescence intensity. The observed phenomena may be explained by an energy diagram in which the ON-VAl complex in AlN:Mn2+ plays a key role. Hence the ON-VAl complex defect in AlN:Mn2+ plays a double role. When the ON-VAl defect is located close to Mn2+ ions, it is responsible for transferring excitation energy directly to Mn2+ ions. However, when the ON-VAl defect complex is located far from Mn2+ ions, its excited state level acts as an electron trap responsible for afterglow luminescence. Additionally, three models have been tested to explain the structure of the emission spectrum and the strong asymmetry between the excitation and emission spectra. From the most straightforward configuration coordinate diagram through the configuration coordinate diagram model assuming different elastic constants in the excited and ground-states ending by a model based on the Jahn-Teller effect. We proved that only the Jahn-Teller effect in the excited 4T1 electronic state with spin-orbit coupling could fully explain the observed phenomena. Finally, high-pressure spectroscopic results complemented by the calculations of Racah parameters and the Tanabe-Sugano diagram are presented.

Luminescence of colloidal quantum points Ag-=SUB=-2-=/SUB=-S/SiO-=SUB=-2-=/SUB=-, decorated by small nanoparticles Au

Ten-fold increase in quantum yield of defect luminescence was found in area 750 nm with simultaneuous growth of its attenuation from 4 to 200 ns, caused by decoration of quantum point (QP) Ag2S/SiO2 (5.0±1.5 nm) surface with nanoparticles (NP) Au (2.0±0.5 nm). Based on analysis of luminescence kinetics at 77 and 300 K the conclusion was drawn on non-specific manifestation of plasmon-exiton interaction caused by polarization effects from NP Au at properties of small traps that participate in generation of defect luminescence kinetics of QP Ag2S/SiO2. Keywords: IR luminescence; luminescence attenuation kinetics; quantum points, plasmon nanoparticles, plasmon-exiton interaction.

Рентгенолюминесцентные свойства пленок оксида цинка на M- и A-плоскостях сапфира

The results of comparative studies of the processes of high-temperature synthesis, luminescence and scintillation characteristics of ZnO films on M(100)- and A(110)-orientation sapphire substrates are presented. It is shown that the use of the magnetron deposition method makes it possible to form, against the background of a continuous film, ensembles of individual [001] ZnO microcrystals with pronounced X-ray luminescent properties. The X-ray luminescence kinetics is characterized by two components: a fast component with a decay time in the order of a nanosecond and a slow luminescence component. The study of the films by photoluminescence spectroscopy revealed the features of the near-band-edge luminescence spectra of the samples, in particular, the presence of various excitonic emission channels. Differences in the spectral parameters of the near-band-edge luminescence band in the case of optical and X-ray excitation are found and interpreted.

X-ray Luminescent Properties of Zinc Oxide Films on the Sapphire M and A-Plane

The results of comparative studies of the processes of high-temperature synthesis, luminescence and scintillation characteristics of ZnO films on M(100)- and A(110)-orientation sapphire substrates are presented. It is shown that the use of the magnetron deposition method makes it possible to form, against the background of a continuous film, ensembles of individual [001] ZnO microcrystals with pronounced X-ray luminescent properties. The X-ray luminescence kinetics is characterized by two components: a fast component with a decay time in the order of a nanosecond and a slow luminescence component. The study of the films by photoluminescence spectroscopy revealed the features of the near-band-edge luminescence spectra of the samples, in particular, the presence of various excitonic emission channels. Differences in the spectral parameters of the near-band-edge luminescence band in the case of optical and X-ray excitation are found and interpreted. Keywords: Films, microcrystals, zinc oxide, X-ray luminescence, photoluminescence, excitonic emission.

A Study of Vanadate Group Substitution into Nanosized Hydroxyapatite Doped with Eu3+ Ions as a Potential Tissue Replacement Material.

In this study, nanosized vanadate-substituted hydroxyapatites doped with 1 mol% and 2 mol% Eu3+ ions were obtained via the precipitation method. To evaluate the structure and morphology of the obtained compounds, the XRPD (X-ray powder diffraction) technique, Rietveld refinement, SEM-EDS (scanning electron microscopy-energy-dispersive spectrometry) and TEM (transmission electron microscopy) techniques as well as FTIR (Fourier transform infrared) spectroscopy were performed. Moreover, the chemical formula was confirmed using the ICP-OES (Inductively coupled plasma optical emission spectroscopy spectroscopy). The calculated average grain size for powders was in the range of 25 to 90 nm. The luminescence properties of vanadium-substituted hydroxyapatite were evaluated by recording emission spectra and excitation spectra as well as luminescence kinetics. The crucial step of this research was the evaluation of the biocompatibility of the synthesized nanomaterials. Therefore, the obtained compounds were tested toward sheep red blood cells and normal human dermal fibroblast to confirm the nontoxicity and biocompatibility of new nanosized Eu3+ ion-doped vanadate-hydroxyapatite. Moreover, the final step of the research allowed us to determine the time dependent ion release to the simulated body fluid environment. The study confirmed cytocompatibility of vanadium hydroxyapatite doped with Eu3+ ions.

Radiative dynamics and delayed emission in pure and doped InP/ZnSe/ZnS quantum dots.

We have used time-correlated single photon counting to elucidate the radiative dynamics of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) that differ in the amount and distribution of excess indium. Stoichiometric QDs having an In:P atom ratio very near unity exhibit simple luminescence kinetics. The photoluminescence (PL) rises with the 40ps instrument response function and exhibits a decay that is close to a single exponential with a time constant that decreases from 32 to 28ns with increasing shell thickness. QDs having excess indium (In:P ratio of 1.15-1.63) show a significant component of a slower rise time assigned to transient population of indium-based hole traps in the ZnSe shell. They also have a slower PL decay, attributed to an equilibrium between these traps, which are optically dark, and the emissive valence-band state. This results in a radiative lifetime that increases from 32 to 48ns with increasing shell thickness. Different treatments of the InP cores prior to shell deposition result in different core/shell interfaces as indicated by resonance Raman spectroscopy, as well as differences in the amplitude and timescale of the slow PL rise and the PL decay time. These are interpreted in terms of different radial distributions of the indium-based hole traps, which can be related to differences in the interfacial lattice strain.