Sr2MgSi2O7 Phosphor Research Articles

Shortwave Ultraviolet Persistent Luminescence of Sr2MgSi2O7: Pr3+

Currently, extensive research activities are devoted to developing persistent phosphors which extend beyond the visible range. In some emerging applications, long-lasting emission of high-energy photons is required; however, suitable materials for the shortwave ultraviolet (UV-C) band are extremely limited. This study reports a novel Sr2MgSi2O7 phosphor doped with Pr3+ ions, which exhibits UV-C persistent luminescence with maximum intensity at 243 nm. The solubility of Pr3+ in the matrix is analysed by X-ray diffraction (XRD) and optimal activator concentration is determined. Optical and structural properties are characterised by photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) spectroscopy techniques. The obtained results expand the class of UV-C persistent phosphors and provide novel insights into the mechanisms of persistent luminescence.

Photoluminescence and Judd-Ofelt analysis of Eu3+ doped akermanite silicate phosphors for solid state lighting

After aluminates, alkaline-earth silicates are the most researched category of luminescent inorganic phosphors. Eu3+ doped Ca2MgSi2O7 and Sr2MgSi2O7 phosphors synthesized by the combustion process. For the as-prepared phosphors, XRD and Rietveld refinement revealed a single phase with akermanite type structure belonging to tetragonal crystallography. UV–Vis spectroscopy was used to calculate the optical bandgap. Ca2MgSi2O7:x%Eu and Sr2MgSi2O7:x%Eu (x = 0.5 - 2.5) phosphors produced orange-red light with emission peaks at 590 nm, 614 nm, and 702 nm, which corresponded to the Eu3+ transitions 5D0 → 7F1, 5D0 → 7F2, and 5D0 → 7F4, respectively. Using a modified Judd-Ofelt technique based on the emission spectrum, the key spectroscopic properties (transition probabilities, radiative lifetimes, and branching ratios) associated with the 5D0 orange-red emitting level were found. Ω2 < Ω4 reveals that Eu3+ ions occupy high symmetry locations in the generated sample under the doping level studied in this work. There has also been a decrease in the Ω4 parameter. It implies that the 5D0 → 7F2 transition is more efficient than the 5D0 → 7F4. This indicates that the red color emission has been improved. The estimated CIE coordinates corroborated the PL emission in the orange-red region.

Role of Eu2+ and Dy3+ Concentration in the Persistent Luminescence of Sr2MgSi2O7 Glass-Ceramics.

In this study, glass-ceramics based on Sr2MgSi2O7 phosphor co-doped with Eu/Dy were obtained from the sintering and crystallisation of glass powders. The glasses were melted in a gas furnace to simulate an industrial process, and the dopant concentration was varied to optimise the luminescence persistence times. The doped parent glasses showed red emission under UV light excitation due to the doping of Eu3+ ions, while the corresponding glass-ceramics showed persistent blue emission corresponding to the presence of Eu2+ in the crystalline environment. The dopant concentration had a strong impact on the sintering/crystallisation kinetics affecting the final glass-ceramic microstructure. The microstructures and morphology of the crystals responsible for the blue emission were observed by scanning electron microscopy–cathodoluminescence. The composition of the crystallised phases and the distribution of rare-earth (RE) ions in the crystals and in the residual glassy phase were determined by X-ray diffraction and energy dispersive X-ray analysis. The emission and persistence of phosphorescence were studied by photoluminescence.

X-ray absorption spectroscopy and neutron-diffraction study of persistent luminescent Sr2MgSi2O7 glass-ceramics

Glass-ceramics based on the Eu2O3/Dy2O3-doped Sr2MgSi2O7 phosphor have been obtained from sintering and crystallization of glass powders. The doped parent glasses show red emission under excitation of UV light. After thermal treatment, the corresponding glass-ceramics show persistent blue emission which emanates from Eu2+ incorporated in the crystals; red emission also occurs from Eu3+ in the residual vitreous phase.The aim of this work is to investigate the structure of defects such as oxygen and strontium vacancies in the Sr2MgSi2O7 crystals and the environment, oxidation state and coordination of the Eu and Dy ions in the glass-ceramics, their partitioning between crystalline and glassy phase and their influence on luminescence properties, employing X-ray absorption spectroscopy (XAS) and neutron diffraction (ND) as investigative structural tools. We suggest that the luminescence mechanism involves the presence of shallow electron traps that are abruptly emptied for temperatures above 100 K. The most persistent luminescence is likely due to an effective concentration of Eu2+ in the dendritic-shaped crystals in one of the particular compositions, and with a suitable level of Sr vacancies, even though Sr vacancies are most likely formed in all the investigated samples.

Processing and luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics

Glass-ceramics based on the Eu/Dy-doped Sr2MgSi2O7 phosphor have been obtained from sintering and crystallization of glass powders. Electric and gas furnaces were employed for glass melting. The doped parent glasses show red emission under excitation of UV light whereas the corresponding glass-ceramics show blue emission.The microstructure of the glass-ceramics and the crystals responsible for the blue emission were observed by scanning electron microscopy-cathodoluminescence. The composition of the crystallised phases and the distribution and incorporation of rare-earth (RE) ions into the crystals and remaining glassy phase were determined by X-ray diffraction and energy dispersive X-ray analysis, respectively.Photoluminescence emission spectra showed a main peak at 484 nm assigned to the typical Eu2+ transitions under excitation at 390 nm in the glass-ceramics. The presence of Dy3+ improved persistence in the samples melted in the gas furnace. The glass-ceramics are sensitive to temperature, which modifies both the persistence time and red-blue luminescence.

Investigation of ultraviolet emitting Gd doped Sr2MgSi2O7 phosphors

This article deals with the ultraviolet (UV)-emitting gadolinium (Gd)-doped strontium magnesium disilicate (Sr2MgSi2O7) phosphors. A series of the Gd-doped Sr2MgSi2O7 phosphors were prepared using a sol-gel method. The powders were well characterized using the X-ray powder diffraction (XRPD) and scanning electron microscope (SEM) techniques. The emission measurements upon a specific UV-light excitation (273 nm) showed the emission characteristics of the Gd3+ that are due to the 6PJ/2 → 8S7/2 transition. EPR spectra of the prepared samples indicated the presence of Gd3+ ions in low symmetry sites in this sample.

Optical properties of novel Sm3+ activated distrontium magnesium disilicate phosphor

The Sm3+ doped Sr2MgSi2O7 phosphors were prepared via solid state reaction method. The prepared phosphors have characterised with X-ray diffraction (XRD), Field emission electron scanning microscope (FESEM), Diffuse reflectance (DR) spectroscopy, Photoluminescence (PL) together with decay curve. The XRD pattern shows the phase purity of the phosphors. In FESEM study the particle shows spherical morphology and consists of particles with irregular and different size distribution. The band gaps of the samples were found to be increased trend corresponding to increase the Sm3+ dopant concentration. The strongest excitation and emission peaks were observed at 402 nm (6H5/2→4F7/2) and 603 nm (4G5/2→6H7/2) respectively. The Sm3+ doped Sr2MgSi2O7 shows yellowish color emission with the excitation wavelength of 402 nm. The prepared phosphor shows excellent thermal stability. The critical concentration of Sm3+ ions in Sr2MgSi2O7 lattice was found to be at 3 mol%. The critical energy transfer distance (Rc) of the prepared sample was found to be 17.36 A. The concentration quenching procedure of the emission in the prepared samples for the transition 4G5/2→6H7/2 was multipole–multipole interaction.

Synthesis, structure, and photoluminescence properties of Ce3+ and Tb3+ doped alkaline-earth silicate Sr2MgSi2O7 phosphors for WLEDs

Abstract

The important role of oxygen vacancies in Sr2MgSi2O7 phosphor

There have been some experimental suggestions about the correlation of the persistent luminescence (PL) mechanism of phosphors with host lattice defects. Oxygen vacancies have most often been invoked, but solid and direct evidence is scarce. We investigate the PL mechanism of Sr2MgSi2O7:Eu2+ on the basis of first-principles calculations of oxygen vacancies. We find that oxygen vacancies occur in a high concentration and introduce a dispersive empty defect band, which is distributed over a wide energy range and located from shallow to deep depth, explaining well the persistent luminescence emission with an intense intensity and a long-lasting duration. Our basic understanding of the general trend of the trap depth and density of O1, O2, and O3 vacancies is applicable to the assignment of the defect structures observe in thermoluminescence spectra. We also propose a possible PL mechanism for Sr2MgSi2O7:Eu2+ phosphor and provide some guides for the search and design of better PL materials.

First-principles study of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material

Electronic structures of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material are investigated using first-principles calculations. Si vacancies are too high in energy to play any role in the persistent luminescence of Sr2MgSi2O7 phosphor. Mg vacancies form easier than Sr vacancies as a result of strain relief. Among all the vacancies, O1 vacancies stand out as a likely candidate because they are the most favorable in energy and introduce an empty triply degenerate state just below the CBM and a fully-occupied singlet state at ~1 eV above the VBM, constituting in this case effective hole trap level and electron trap levels, respectively. Mg vacancies are unlikely to explain the persistent luminescence because of its too shallow electron trap level but they may compensate the hole trap associated with O1 vacancies. We yield consistent evidence for the defect physics of these vacancy defects on the basis of the equilibrium properties of Sr2MgSi2O7, total-energy calculations, and electronic structures. The persistent luminescence mechanism of Sr2MgSi2O7:Eu2+, Dy3+ phosphor is also discussed based on our results for O1 vacancies trap center. Our results provide a guide to more refined experiments to control intrinsic traps, whereby probing synthetic strategies toward new improved phosphors.

Structure, surface analysis, photoluminescent properties and decay characteristics of Tb3+-Eu3+ co-activated Sr2MgSi2O7 phosphor

Tb3+-Eu3+ co-activated Sr2MgSi2O7 powder phosphors were synthesized by a solid-state reaction method. The structure, stretching vibrations, chemical and electronic states, and photoluminescent properties were studied using X-ray powder diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Time-of-flight secondary ion mass spectrometer (TOF-SIMS) and Photoluminescence (PL) spectroscopy respectively. The XRD pattern of the Sr2MgSi2O7:Eu3+, Tb3+ phosphor resembles the standard tetragonal phase of Sr2MgSi2O7. The fitted XPS data demonstrated that there were two different Sr2+ sites in the host lattice and a site occupied by Mg+ cations which connects the Sr+ sites with the Si+ ions. The TOF-SIMS results demonstrated localization and distribution of various ions within the host lattice (Sr2MgSiO7) including the Tb3+ and Eu3+ dopants. The photoluminescence of Tb3+ single doped Sr2MgSi2O7 shown to emit blue and green emissions simultaneously with green emission more intense and the blue emission improving considerably when lower concentrations of Tb3+ were used. Only red emission was observed from the Eu3+ single doped Sr2MgSi2O7. Upon Tb3+-Eu3+ co-doping, simultaneous emissions of blue, green and red lines were observed resulting in white emission.

Photoluminescence properties of Tb3+ and Ce3+ co-doped Sr2MgSi2O7 phosphors for solid-state lighting

Sr2MgSi2O7:Tb3+,Ce3+ phosphors were synthesized by solid-state reaction and placed in a muffle furnace in a reducing atmosphere at 1300 °C for 3 h. Photoluminescence properties and energy transfer were investigated. The Ce3+/Tb3+ energy transfer was thoroughly investigated by their emission/excitation spectra and photoluminescence lifetime, there was shortened lifetime of Ce3+ (from 51.31 to 50.06 ns) which could support evidence of energy transfer from Ce3+ to Tb3+ in the host. The varied emitted color of Sr1.97–yMgSi2O7:0.03Tb3+, yCe3+ phosphors could be achieved by altering the concentration of Ce3+, the chromaticity coordinates (x, y) varied from (0.225, 0.376) to (0.172, 0.231). In Sr1.96MgSi2O7:0.03Tb3+,0.01 Ce3+ phosphors, the results indicated that Sr2MgSi2O7:Tb3+,Ce3+ might be useful as tunable phosphors for ultraviolet white-light-emitting diodes.

Studies on white light emission of Sr2MgSi2O7 doped with Dy3+ phosphors

Present paper reports the preparation of Sr2MgSi2O7 doped with Dy3+ ions by modified high temperature solid state reaction technique. Samples were prepared for different concentration of Dy3+ (0.5, 1.0, 1.5, 2.0 and 2.5mol%). Sample with optimum photoluminescence intensity was characterized by X-ray diffraction (XRD) technique. Observed XRD spectrum matched with crystallographic open database card specifically appeared for Sr2MgSi2O7 phosphor. This is a confirmation of proper preparation of the sample. Photoluminescence studies of these samples were done. Emission spectra exhibited 5 prominent peaks at 480, 490, 575, 590 and 660nm respectively. In this case Dy3+ acts as an activator. Peaks centered at 480 and 490nm are due to the transition 4F9/2→6H15/2 (blue color) of Dy3+ ions occupied at different sites. Similarly 575 and 590nm peaks are originated due to transition 4F9/2→6H13/2 (yellow–orange color) of Dy3+ ions occupied at different sites. Emission at 660nm is due to transition 4F9/2→6H11/2 (red color). CIE coordinates have been calculated for each sample and its value exhibited that, overall emission is near white light. In order to investigate the suitability of the samples as white color light sources for industrial uses, correlated color temperature (CCT) and color rendering index (CRI) were calculated. Values of CCT and CRI were found, well within the defined acceptable range.

A new phosphor with flower-like structure and luminescent properties of Sr2MgSi2O7: Eu2+, Dy3+ long afterglow materials by sol–gel method

The flower-like phosphors of Sr2MgSi2O7: Eu2+, Dy3+ with high brightness and long afterglow were obtained by sol–gel method. X-ray diffraction pattern (XRD) shows that single-phased Sr2MgSi2O7 phosphor is prepared by sol–gel method under 1250 °C. Scanning electron microscope (SEM) indicates that the phosphor consists of nano-sized whiskers which are detected for the first time in Eu2+ and Dy3+ co-doped long-lasting phosphorescence silicates. Furthermore, the investigation on the mechanism indicates that the internal structure and gas, liquid and solid phase effect play important roles in the formation of flower-like Sr2MgSi2O7: Eu2+, Dy3+ nanostructure. Finally, the optical properties of flower-like Sr2MgSi2O7 nanostructure have been characterized by photoluminescence (PL) spectra.