Integrated Luminescence Intensity Research Articles

Emission behaviour of CdTe/SiO2 core/shell quantum dots in external electric field

Optical properties of CdTe/SiO2 core/shell colloidal quantum dots were investigated in external electric field in the range of 0–140 kV/cm. Maximum of photoluminescence intensity was centered at 2.39 eV with the full width at half maximum of 0.26 eV. It was found that the photoluminescence intensity of quantum dots tends to decrease by 22% and the integrated luminescence intensity tends to decrease by 23% with increasing electric field to the maximum value. However, an increase in the integrated luminescence intensity in the region of 60 kV/cm was observed. We show that both interband and trap-state luminescence is affected by an external electric field with no Stark shift observed. Based on these results, we propose that relaxation of the excited states in CdTe/SiO2 core/shell colloidal quantum dots exposed to an external electric field is affected by two field-dependent mechanisms, i.e. field-induced quenching of luminescence and blocking of charge carrier trapping. The obtained results can be useful to gain better understanding of the electric field effect on the optical properties of CdTe/SiO2 colloidal semiconductor quantum dots and, in particular, on the operation of hybrid organic-inorganic LEDs with emitting layers based on the studied nanocrystals.

LiGdxY1−xF4 and LiGdF4:Eu3+ Microparticles as Potential Materials for Optical Temperature Sensing

In this work, the physical characterization of LiGdxY1−xF4 (x = 0.05, 0.3, 0.7, and 1.0) and LiGdF4:Eu3+ microparticles was performed. The distribution coefficient of LiGdxY1−xF4 (x = 0.05) was determined for the first time (0.84). Based on kinetic characterization data, the LiGdF4 sample was chosen for further Eu3+ doping (0.1 and 1.0 at.%). For the LiGdF4:Eu3+ sample, Eu3+ emission was clearly observed under the excitation of Gd3+. This fact indicates an effective energy transfer from Gd3+ to Eu3+. The temperature-dependent spectral characterization of the LiGdF4:Eu3+ (1.0%) sample revealed that in the 30–250 K temperature range, a broad emission peak is evidenced. Its intensity sharply increases with the temperature decrease. We made a suggestion that this phenomenon is related to the irradiation-induced defects. The integrated luminescence intensity ratio of this broad peak and the Eu3+ emission were taken as temperature-dependent parameters. The sensitivity values are very competitive, and the first maximum occurs at 174 K (3.18%/K). The kinetic characteristics of both Gd3+ and Eu3+ did not demonstrate a notable temperature dependence. The LiGdF4:Eu3+ sample showed the possibility of being used as an optical temperature sensor, operating in the cryogenic temperature range.

Infrared Glow of Nitric Oxide in Earth’s Middle Atmosphere during GLE Events of the 23rd Solar Cycle

The article considers the production kinetics of vibrationally excited NO(X2Π, 0) molecules at heights of Earth’s middle atmosphere during the precipitation of high-energy protons. The intensity profiles of the luminescence of the infrared bands of nitric oxide at 5.3 and 2.7 μm were calculated for precipitation of high-energy protons into Earth’s atmosphere during the events GLE65, GLE67, GLE69, and GLE70 of the 23rd solar cycle. Calculations have shown that the highest integral luminescence intensity values of the 5.3 and 2.7 μm bands were obtained for GLE69: 5.7 and 0.18 kR (kilorayleighs), respectively. Comparison of the calculation results for the 5.3 µm band during the GLE69 event with experimental data obtained from the TIMED spacecraft on January 20, 2005, showed that the calculation results were overestimated by a factor of 2.

Efficient broadband yellow-emitting Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ garnet phosphors for blue-light-pumped white light-emitting diodes

The discovery of yellow-emitting phosphors with higher luminescence intensity and wider bandwidth than the commercial Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor upon blue light excitation remains one of the significant challenges for establishing human-centered warm white light-emitting diode towards high-performance illumination. Herein, we innovatively synthesized a novel Ce3+-activated broadband yellow-emitting garnet phosphor of Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ (MLASO:Ce3+) via conventional high-temperature solid-state reaction method. The as-prepared MLASO:10%Ce3+ garnet sample possesses a cubic structure with Ia3‾d space group and lattice parameters of a = b = c = 11.85098 Å and V = 1664.421(0.044) Å3. Luminescence spectroscopy tests indicates that the optimal MLASO:10%Ce3+ yellow-emitting phosphor features 1.2 times higher relative integral luminescence intensity and an impressive full width at half maximum (FWHM) of up to 145 nm with respect to the most extensively available commercial YAG:Ce3+ phosphor (FWHM = 122 nm) under the identical blue light irradiation, which can provide more red-components for improving color rendering index. Additionally, the CIE color coordinates and a satisfactory internal quantum efficiency are determined to be (0.4751,0.5028) and 74%, respectively. More importantly, the representative optimal sample can preserve 77% luminescence emission intensity at a 423 K high temperature thermal treatment environment compared to the ambient temperature. As a result, this study sheds light on newly discovered broadband yellow-emitting MLASO:10%Ce3+ garnet phosphor containing more of the red chromatic spectrum can sever as one of the promising color-conversion-materials in high-performance white LEDs with high color rendering index for healthy solid-state lighting.

Characterization of YAG:Ce ceramics with graphene oxide

Yttrium-aluminum garnet (Y3Al5O12) is an optical material that shows great potential due to its favorable light-emitting and mechanical properties, as well as its chemical stability and thermal resistance. It is commonly utilized in laser technology, optical instruments, and solid-state light sources as a result of its activation by transition metal or rare earth element ions. In this work, experiments were carried out on the procedure for compacting samples of luminescent ceramics Y3Al5O12:Ce3+, by single-base pressing followed by sintering. Comprehensive studies of the influence of graphene oxide of variable concentration (x=0.1;0.5; 1 wt.%) on the radiative characteristics of ceramic samples. It was found that the addition of graphene oxide in an amount from 0.1 to 1 wt. % affects the density and luminescent properties of YAG:Ce ceramics. There is a decrease in the value of the density parameter at concentrations of graphene oxide 0.1-1 wt. % before annealing, after annealing, the relative density value increases to ~99 %. The luminescence spectrum when excited by a blue LED chip appears as a wide band in the spectral range 460-750, the nature of which is associated with radiative transitions in the cerium ion. It has been established that the light-emitting characteristics have a downward trend when activated by graphene oxide. The integral luminescence intensity decreases from 27.1 % to 19 % with an increase in the concentration of graphene oxide.

Enhancement of broad-spectrum orange emission and thermal stability in Rb2-xCsxCaP2O7:0.015Eu2+ phosphors by improving local structural symmetry

The tunable 5 d-4f luminescence of Eu2+ is of great application value, but it is still full of challenges in terms of luminescence efficiency, thermal stability and precise tuning of luminescence colors. In this work, we synthesized a series of Rb2-xCsxCaP2O7:0.015Eu2+ phosphors based on the equivalent substitution strategy, allowing a certain proportion of Cs+ to replace Rb+ sites. By optimizing the Rb/Cs ratio, the structural symmetry of the [CaO6] octahedra can be enhanced, providing a high-stability and high-symmetry localized crystal field environment for the high efficiency luminescence of Eu2+. The experimental results confirmed that the broad-spectrum orange light emission could be achieved in Rb0·5Cs1·5CaP2O7:0.015Eu2+, and the integrated luminescence intensity was 6.9 times higher than that of Rb2CaP2O7:0.015Eu2+. Moreover, the luminescence intensity at 150 °C reached 93.3% of its room-temperature value. Using the synthesized phosphor as orange component, a white LED was assembled and a high-quality white light emission with Ra = 87.8 was achieved. These results suggest that rationally tuning the local structural symmetry around Eu2+ is an effective strategy to develop high-performance Eu2+-activated phosphors.

Influence of silver nanoparticles in the ion-exchange layer of photo-thermo-refractive porous glass on the spectral-luminescent properties of CsPbBr3 perovskite nanocrystals

The spectral-luminescent properties of new composite materials based on porous matrices of photo-thermo-refractive glasses with a silver ion-exchange layer and CsPbBr3 inorganic perovskite nanocrystals have been studied. Perovskite nanocrystals were introduced into a porous matrix by the method of pumping solutions through a sample under piston pressure. Two mechanisms of interaction between silver nanoparticles and perovskite nanocrystals have been revealed, such as enhancement of the local field and luminescence quenching due to the high absorption of nanoparticles. The quantum yield of the studied samples under different irradiation associated with an increase in the concentration of silver nanoparticles was 34% without irradiation, 51% with 100 j irradiation dose, and 25% with 1000 j irradiation dose. In this case, an increase in the integrated luminescence intensity was observed in glasses irradiated with 100 J by a factor of 2.97 and irradiated with 1000 J by a factor of 1.76 compared to the unirradiated sample. The average luminescence lifetime decreases from 2.19 to 1.68 ns with an increase in the concentration of nanoparticles.

ЗАВИСИМОСТЬ СОСТАВА И ЛЮМИНЕСЦЕНТНЫХ ХАРАКТЕРИСТИК ЛЮМИНОФОРОВ ОТ ТЕМПЕРАТУРЫ ПИРОЛИЗА ПРЕКУРСОРОВ

General conditions for the synthesis of phosphors based on mixed oxides of REE and rare elements by the low-temperature extraction-pyrolytic method were discussed. Dependence of morphology, composition and relative integrated luminescence intensity of phosphors on the pyrolysis temperature of precursors was investigated.

Performance of the Li6Eu(BO3)3 crystal as a scintillating bolometer for studies of rare processes

In this article we report on a detailed study of the internal radioactive and chemical contamination of the Li6Eu(BO3)3 scintillating crystal operated as a cryogenic scintillating bolometer over 359 h. The excellent discrimination power of the detector allows to distinguish effectively beta/gamma events from alpha events. Whilst a weak activity of daughter nuclides from U/Th chains at the level few mBq/kg was observed, this crystal was found to be significantly contaminated by 147Sm, an alpha-active nuclide, at the level of about 0.5 Bq/kg. The light yield for β/γ events was determined to be 7.4(6) keV/MeV. The light yield and quenching factor for alpha particles vary in the range of (0.5–1.2) keV/MeV and (0.07–0.17), respectively, due to energy dependence of the emitted scintillating light in the energy interval (2.0–7.0) MeV. The integral luminescence intensity of the Li6Eu(BO3)3 crystal increases by more than four times only at low temperatures, below 80 K. Therefore, the Li6Eu(BO3)3-based cryogenic scintillating bolometers can be attractive detectors for direct neutron flux monitoring, to search for rare alpha decays or solar axions.

Optical characteristics of Tl+ centers in CsCaCl3, KCaCl3, and CsCl crystals

We have investigated the absorption, luminescence, and excitation spectra of the Tl+ centers in CsCaCl3:Tl+, KCaCl3:Tl+, and CsCl:Tl+ crystals in the energy region up to the vacuum ultraviolet region. The A, B, and C absorption bands attributed to the intra-ionic transitions were observed in the transparent energy region below their respective fundamental absorption edge. The parameters characterizing the Tl+ centers were estimated by the energy positions of the A, B, and C absorption bands and the absorption intensity ratio of the C to A bands. These values are consistent with those of the Tl+ centers in other ionic chloride crystals. The luminescence bands attributed to the radiative transitions from several relaxed excited states were observed even under excitation of the A absorption band. Although the intensities of the luminescence bands change with an increase in temperature from low temperature, the total integrated luminescence intensity remained almost constant. The temperature dependence of the luminescence intensity can be explained by the thermally activated non-radiative transitions among the relaxed excited states and the radiative transitions from them. By including the Tl+ centers in alkali and ammonium chloride crystals, the features of the Tl+ centers in the resulting chloride compound crystals have been comprehensively discussed regardless of the different chloride-ionic configurations around the Tl+ ions.

Influence of synthesis conditions on structural and spectroscopic properties of the K2SrP2O7 pyrophosphate doped with the Eu3+ and Eu2+ ions

This study is focused on the synthesis condition influence related to structural and spectroscopic properties of the potassium strontium pyrophosphate (K2SrP2O7) co-doped with Eu3+ and Eu2+ ions. The experimental parameters of the urea assisted combustion synthesis were optimized by temperature and time of calcination as well as reduction atmosphere composition. The obtained materials were structurally characterized using the X-Ray Powder Diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Spectroscopic properties were determined by emission spectra, excitation spectra, luminescence kinetics and luminescence temperature quenching measurements. It was found that increasing concentration of Eu3+ ions caused an increase of spectroscopic factors, which correspond to the relative integrated luminescence intensities of 5D0–7FJ transitions as well as structural defects. Moreover, the successful Eu2+ ion incorporation was proven by optical spectroscopic measurements, which showed the allowed f-d transitions.

Microwave-hydrothermal synthesis and investigation of Mn-doped K2SiF6 microsize powder as a red phosphor for warm white LEDs

Microsize powder of Mn-doped potassium hexaflourosilicate (PFS, K2SiF6) phosphor has been synthesized using the microwave-hydrothermal (MWHT) method, a new approach for obtaining this material. Special attention has been paid to the identification of the valence states for Mn doping ions using EPR and XANES techniques. Although photoluminescence results reveal luminescence properties typical for Mn4+ ions, the XANES spectra show the presence of Mn ions in various valence states (+2 to +4). The analysis of the temperature dependence for the Mn4+ integrated luminescence intensity and luminescence decay time has shown that the MWHT synthesis provides better performance of the PFS phosphor compared to that of commercially available PFS phosphors in respect of higher thermal stability because of improved crystallinity and lower concentration of defects. It has been revealed that above 500 K, Mn4+ luminescence decay becomes non-exponential due to the energy transfer to defect quenching centers. Repeated thermal treatment of microparticles up to 700 K results in considerably changed thermal quenching parameters due to the transformation of K2SiF6 into the K3SiF7 phase. The latter compound doped with Mn4+ shows spectral properties very similar to those of K2SiF6:Mn4+ but demonstrates better thermal stability and shorter decay time of Mn4+ luminescence at normal conditions which can make the red-emitting K3SiF7:Mn4+ phosphor a promising candidate for application in wLEDs.

Optical Glass with γ-Ga2O3 Nanocrystals for UV-C Radiation Visualization

Glass meeting the GOST requirements concerning stria-free category-1 optical glass was produced in the system Me2O–Ga2O3–GeO2–SiO2 (Me = Li, Na). The subsequent heat treatment results in the precipitation of γ-Ga2O3 nanocrystals in it and triggering of luminescence excited by only UV radiation in the solar-blind range. The integral visible-light transmission and luminescence intensity of the developed material are comparable with these characteristics of glass-crystalline samples for which the glass was obtained by the melt quenching method.

Tunable white light emission from Dy3+/Eu3+ doped LaAlO3 nanophosphors via hydrothermal method

A sequence of Dy3+/Eu3+ co-doped LaAlO3 nanophosphors are synthesized by hydrothermal technique and their phase purity, particle nature and luminescence characteristics are investigated. All the prepared samples possess single-phased perovskite type rhombohedral structure of LaAlO3 and consist of polygonal natured particles with the mean size of 30 nm. Under the excitation with 351 nm, LaAlO3: Dy3+ nanophosphors shown characteristic emission peaks of Dy3+ ion and are positioned at 485, 576 and 665 nm. LaAlO3: 9 mol% Dy3+, y mol% Eu3+ nanophosphors exhibited emission bands of both Dy3+ and Eu3+ ions and are noticed at 485, 576, 590, 620 and 696 nm under 351 nm excitation. It can be perceived that the Dy3+ integrated luminescence intensity is reduced and the average lifetime of Dy3+ is decreased with the enhancing Eu3+ content, which is owing to energy migrates from Dy3+ ion to Eu3+ ion. Moreover, CIE coordinate values of LaAlO3: 9 mol% Dy3+, y mol% Eu3+ nanophosphors are altered from the bluish-white to white light and ultimately to the orange-white light location with increasing the Eu3+ ion content. This nature of color adjustable nanophosphors shows the excellent potential advantages in the fields of white light luminescent materials, optoelectronic devices and color displays.

Impact of excitation energy on the excitonic luminescence of cesium lead bromide perovskite nanosheets.

An excitation-energy-dependent luminescence phenomenon is reported in cesium lead bromide (CsPbBr3) perovskite nanosheets. At 10 K, the relative integrated luminescence intensity between the trapped exciton (TX) emission and the free exciton (FX) emission shows an interesting tendency with increasing the optical excitation energy from 2.431 eV (510 nm) to 3.758 eV (330 nm). To interpret such phenomenon, we develop a quantitative model on the basis of the biological population growth theory. A good agreement between experiment and theory is obtained. It is thus revealed that the lower capture coefficient of the TX level to the excited excitons via multiphonon emission relative to the FX level shall be the major cause of the observed phenomenon. These findings may help to deepen the current understanding of the complex luminescence mechanisms of these emerging light-emitting materials.

A novel Al3+ modified Li6CaLa2Sb2O12:Mn4+ far-red-emitting phosphor with garnet structure for plant cultivation

A novel-far red emission Li6CaLa2Sb2O12 (LCLSO):Mn4+ phosphor was prepared by traditional high temperature solid state reaction method. The morphology, spectral characteristics and luminescence properties of the phosphors were all studied systematically. Based on the results, when x = 0.0045 (x represents the doping concentration of Mn4+), the emission intensity of LCLSO:xMn4+ phosphor reaches the maximum, and the concentration quenching occurs after the Mn4+ doping concentration exceeds 0.0045. In addition, the effect of Al3+-doped on the luminescent properties of the materials was also studied. The optimum doping concentration of Al3+ is y = 0.009 (y represents the doping concentration of Al3+), and the luminescence intensity of Mn4+ can be increased about 4 times. Moreover, the integrated luminescence intensity, the thermal activation energy, and decay time can be obtained via calculation. In summary, LCLSO:Mn4+, Al3+ phosphor exhibits good luminescence efficiency and thermal stability, and possesses the latent application foreground in plant growth lighting.

Luminescent properties of nanocomposite - Bi12SiO20, filled with C6H9EuO6 × H2O

The work presents the results of the study of the photoluminescence spectra of the (111) growth surface of an opal - Bi12SiO20 matrix nanocomposite filled with europium (III) acetate hydrate (C6H9EuO6 × H2O). An increase in the integral luminescence intensity of the matrix composite opal - Bi12SiO20: Eu3+ compared to composite opal: Eu3+ was found. The measured photoluminescence spectra of the Bi3+ ions in the opal pores indicate its participation in optical processes as a co-activator of luminescence. A change in the character of the splitting of the main luminescence bands of Eu3+ ions in the region of 575–635 nm and the integral luminescence intensity after dehydration of the crystalline hydrate in opal pores has been established.

All-fibre single-mode small-signal amplifier operating near 0.976 μm

We have developed and demonstrated a polarisation-maintaining single-mode ytterbium-doped fibre for light amplification at a wavelength near 0.976 μm in an all-fibre configuration. A distinctive feature of the proposed fibre design is low losses due to fusion splices with standard single-mode fibre having a core diameter of 10 μm, which has made it possible to produce an all-fibre small-signal amplifier with a gain threshold near 3 W and a differential pump-to-signal conversion efficiency of 9.8 % in the saturation regime. The proposed amplifier has been shown to be well-suited for small-signal amplification. In particular, at an input signal power near 1 mW and a gain of 20 dB, the ratio of the amplified signal to the integrated luminescence intensity near 0.976 μm exceeds 20 dB. A 40-dB gain has been demonstrated for an ultrasmall signal of ∼10-μW power.

Brightening upconverting nanocrystals using laser-induced surface reconstruction

Upconversion nanoparticles exhibit ordinary emission brightness for the existence of non-radiative transition induced by the surface defects, which fundamentally limits their promising applications. Here, a reconstruction process to rule out the amorphous layer and defects related to the surface of the as-synthesized particles is achieved with the use of 980-nm continuous laser irradiation. More importantly, the uniform morphology and monodispersibility of these nanoparticles are well preserved. Local heat induced via photothermal conversion of laser irradiation with the association with non-harmonic phonon coupling contributes to a tremendous improvement on the integral upconversion luminescence intensity. The upconversion intensity of Er3+ ions in sub–10-nm Ba2LaF7 nanoparticles enhances by more than 313-fold in the red emission, and subsequently, a bright luminescence originated from an individual particle could be observed under a multiphoton laser scanning luminescence microscopy. Our results suggest that this strategy could be extended to GdF3, KLu2F7, and BaGdF5 systems, which exhibit drastic enhancement of emission intensity unambiguously. The laser-induced surface reconstruction in this work is demonstrated to provide a direct and facile approach to enhance the upconversion intensity, which could offer the possibility for achieving high-resolution imaging.

Luminescence Spectra of C6H9EuO6 x H2O Doped Synthetic Opals Matrix Containing Bi-Active Dielectrics

This paper presents the results of experimental studies for the luminescence spectral intensity redistribution of opal photonic crystals containing various active dielectrics - Bi12SiO20, opal - Bi2TeO5 and opal - NaBi(MoO4)2 matrix nanocomposites and filled with europium C6H9EuO6 x H2O salt. Ultraviolet excitation was provided by semiconductor laser operating at wavelengths of 400nm and 100 mW average power. An increase in the integral luminescence intensity of the matrix composite opal - Bi12SiO20: Eu3+ was found. The possibility of the participation of bismuth ions as a co-activator and luminescence concentrator also is analyzed. It has been proposed to use opal-Bi12SiO20 nanocomposite filled with europium as a potentially attractive material to improving the solar cell efficiency.