Doped Silicate Phosphors Research Articles

Eu2+ doping and Mg2+-coupled Zn2+, Ca2+ and Sr2+ cations induce tunable orange-blue luminescence in cordierite

A series of Mg2Al4Si5O18:xEu2+ (x = 0.2, 0.6, 1.4, 2.8, 6.0mol‰) and Mg2Al4Si5O18:0.05B, 1.4Eu2+ (BZn2+, Ca2+ and Sr2+) phosphors were prepared by high-temperature melt ice-water quenching and heat treatment. In this study, using Eu2+ ions as a structural probe, we investigated the effects of heat treatment temperature, Eu2+ ion concentration, and cation position on the crystal phase and local structure, triggering changes in the luminescent properties of the phosphor and achieving coordinated blue and red luminescence. Through heat treatment analysis, we proposed the formation process of the two phases of cordierite. The doping of different concentrations of Eu ions in cordierite triggers the phase transition of the host lattice. The molar distribution ratio of Eu2+ ions was calculated by Gaussian peak-splitting fitting to identify the detailed occupancy distribution of the Eu2+ ions in μ-cordierite and α-cordierite. In the α-cordierite phase, with the doping of Zn2+, Ca2+, and Sr2+ cationic sites, the PL is modulated from orange to blue emission based on the selective occupancy of Eu2+ ions, which is caused by the difference in cationic radii and structural distortion. The comprehensive luminescence intensity of MASE1.4, MASZ0.05E1.4, MASC0.05E1.4, and MASS0.05E1.4 phosphors were 81.18%, 83.49%, 62.67%, and 76.41% at 150 °C compared to that at 30 °C, indicating the better thermal stability of the prepared phosphors. The luminescence tunable strategy by cation and Eu2+ doping simultaneously modifies the emission and achieves different thermal stability, providing a new design concept for the development of Eu2+-doped silicate phosphors.

Simultaneous realization of tunable luminescence and enhanced thermal stability in Eu2+-based blue-green phosphors for multifunctional applications

Developing a new Eu2+-doped blue-green phosphor with tunable spectral in silicate materials is challenging for a high-quality phosphor-converted white light-emitting diode. The cation substitution strategy is a valid way to concurrently modify spectral characteristics and optimize luminescence performances. Herein, a series of NaBaScxLu1-xSi2O7: Eu2+ phosphors with blue-green color-tunable luminescence have been designed. By modulating the ratio of Sc/Lu, controllable regulation of the photoluminescence and thermal stability properties can be realized simultaneously. Moreover, the initial emission intensity is monotonically increased by 2.92 times and the quantum efficiency is enhanced dramatically by introducing Sc3+. Especially, the thermal stability is boosted from 53.4% to 90.9% and the emission shifted from 485 to 504 nm is improved due to the chemical substitution of Sc in the Lu site with the lattice shrinks resulting in the Eu5d energy level farther away from the conduction band and a minimum 5d energy level closer to the ground state energy level. Furthermore, the fabricated w-LEDs with NaBaScxLu1-xSi2O7: Eu2+ blue-green phosphors and (Sr, Ba)3SiO5: Eu2+ red phosphor exhibit a high color rendering index (Ra = 87.2) and desired color-dependent temperature (CCT = 3711 K). Except for the application in solid-state illumination, the potential application of synthetic phosphors in optical anti-counterfeiting is also explored. The luminescence tunable strategy via cation substitutions simultaneously modifies emission and improves thermal stability, providing a distinctive design philosophy for the development of Eu2+-doped silicate phosphors.

Single-Phase Silicate Phosphors (Ba1.3Ca0.7−xSiO4:xDy3+) Doped with Dysprosium for White Solid-State Lighting

Single-phase phosphors have potential advantages such as simple processability, competitive cost, and other optical and optoelectronic properties. Hence, in this study, the silicate phosphors (Ba1.3Ca0.7−xSiO4:xDy3+) doped with Dy3+ ions (x = 0.01–0.05) were synthesized and characterized in detail. X-ray diffraction patterns showed that all the silicate phosphors have a τ-phase hexagonal unit cell independent of doping. However, d-spacing was reduced for the doped samples, indicating that the interplanar interactions were enhanced. Resultantly, the doped phosphors exhibited relatively larger domains with connectivity than the host, although there were sometimes microscale pores. Photoluminescence spectra stipulated that the optimized doping concentration is x = 0.03 for the silicate Ba1.3Ca0.7-xSiO4:xDy3+ phosphors. Finally, the CIE coordinates (0.30, 0.33) confirm that the Dy3+-doped silicate phosphors are well applicable to the white light-emitting diodes for solid-state lighting and display devices.

Data-Driven Photoluminescence Tuning in Eu2+-Doped Phosphors.

Discovery of rare earth phosphors has generally relied on the chemical intuition and time-intensive trial-and-error synthesis; therefore, finding new materials assisted by data-driven computations is urgent. Herein, we utilize a regression model to predict the emission wavelengths of Eu2+-doped phosphors by revealing the relationships between the crystal structure and luminescence property. The emission wavelengths of [Rb(1-x)K(x)]3LuSi2O7:Eu2+ (0 ≤ x ≤ 1) phosphors, as examples for the data-driven photoluminescence tuning, are successfully predicted on the basis of the existing data of only eight systems, also consistent with the experimental results. These phosphors can be excited by blue light and exhibit broad-band red and near-infrared emission ranging from 619 to 737 nm. These findings in Eu2+-doped silicate phosphors indicate that data-driven computations through the regression mode would have bright application in discovering novel phosphors with a target emission wavelengths.

Synthesis and luminescence properties of novel red-emitting Eu3+ ions doped silicate phosphors for photonic applications

In the present work, we report on luminescence properties of Eu3+ ions doped KBaScSi3O9 silicate phosphors (KBSS) synthesized by high temperature solid state reaction method and the prepared phosphor samples were characterized through XRD, FE-SEM, photoluminescence and decay spectral measurements. The XRD pattern confirmed that the KBSS host lattice exhibited a monoclinic crystal structure. Room temperature photoluminescence (PL) spectroscopic results reveal that, on Eu3+ ion doping in the KBSS host matrix, the magnetic dipole transition (5D0 → 7F1) at 593 nm responsible for orange light, dominates the red emission with respect to the electric dipole transition (5D0 → 7F2) at 611 nm. The Judd-Ofelt (JO) intensity parameters Ωλ (λ = 2 and 4) have been calculated from the emission spectra to understand the nature of ligand environment around the Eu3+ ions. The radiative parameters, such as transition probability (A), stimulated emission cross-section (σPE), radiative lifetime (τR) and branching ratios (βR) corresponding to the 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 emission transitions have been determined by using JO parameters and the refractive indices respectively. The concentration quenching effect for Eu3+ was found at the optimum doping concentration of 7 mol %. The CIE chromaticity coordinates were calculated from the luminescence spectra to explore the dominant emission colour of the title phosphors. The experimental lifetime values of 5D0 level of the Eu3+ doped silicate phosphors have been calculated and the obtained results were discussed in detail.

Thermoluminescent behavior of UV and γ rays irradiated Eu2+ and Er3+doped silicate phosphors

Abstract This paper reports the structural, morphological and thermoluminescent studies of Eu2+ and Er3+ ions activated ASiO3 (A = Ca, Ba, Sr) phosphors synthesized via conventional solid state reaction method. The impurity ions concentration of both Eu2+ and Er3+ ions varies from 0 mol% to 1 mol%. The study of crystallographic traits of the synthesized phosphors is done by Powder X-Ray Diffraction (PXRD) analysis. The crystalline nature, phase purity and appreciable homogeneity of the synthesized phosphors were confirmed by this study. The distinct morphological and topographical features were studied through Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The thermoluminescent (TL) behavior of ultraviolet (UV) irradiated and gamma irradiated ASiO3:Eu2+, Er3+ (A = Ca, Ba, Sr) phosphors were studied here and the various kinetic parameters were estimated by Computerised glow curve deconvolution (CGCD) technique and peak shape method. The UV and gamma irradiated phosphors exhibit second order kinetics. The high values of activation energy (∼3 eV) confirm the trapping of electrons in deep trap centers. The incorporation of doping ions into the host lattice causes non-valence substitutions at the substitutional sites. This increases the number of defects and vacancies in the phosphors and more trap centers were generated. The increased TL intensity and high temperature glow peaks confirm the same. The synthesized phosphors show enhanced TL characteristics, efficient trapping mechanism and low fading effects. These characteristics confirm the suitability of the synthesized phosphors for TL mapping and sensing applications.

A near-ultraviolet (NUV) converting blue-violet Mg2SiO4:Ce3+ phosphor for white light-emitting-diodes (w-LEDs)

Ce3+-doped silicate phosphors (Mg2-xSiO4:xCe3+, x = 0.001–0.007 mol) for NUV w-LEDs have been synthesized by solid-state reaction method at 1450°C. The as-prepared samples have been characterized by XRD and fluorescence spectrophotometer, respectively. The XRD results show that the aim phase has been synthesized and doping Ce3+ has not resulted in impurity phase. This phosphor material exhibits a strong blue-violet emission (330–520 nm) under the near-ultraviolet radiation excitation. The average colorimetric coordinate of Mg2-xSiO4:xCe3+ (x = 0.0025 mol) is (0.1508, 0.0694), locating in blue-violet region. We have obtained bright blue-violet light via pumping the sample by NUV light (λ ≈ 365 nm), suggesting that this material can be potential as a NUV converting blue-violet phosphor for the NUV w-LEDs.

Enhancing Photovoltaic Performance Using Broadband Luminescent Down-Shifting by Combining Multiple Species of Eu-Doped Silicate Phosphors.

This paper demonstrates the application of a broadband luminescent downshifting (LDS) layer with multiple species of europium (Eu)-doped silicate phosphors using spin-on film technique to enhance the photovoltaic efficiency of crystalline silicon solar cells. The surface morphology of the deposited layer was examined using a scanning electron microscope (SEM). The chemical composition of the Eu-doped silicate phosphors was analyzed using energy-dispersive X-ray spectroscopy (EDS). The fluorescence emission of the Eu-doped silicate phosphors was characterized using photoluminescence (PL) measurements at room temperature. We also compared the optical reflectance and external quantum efficiency (EQE) response of cells with combinations of various Eu-doped phosphors species. The cell coated with two species of Eu-doped phosphors achieved a conversion efficiency enhancement (∆η) of 19.39%, far exceeding the ∆η = 15.08% of the cell with one species of Eu-doped phosphors and the ∆η = 8.51% of the reference cell with the same silicate layer without Eu-doped phosphors.

Shortwave Triboluminescence of Ce Doped Silicate Phosphor in Sliding Friction and its Potential Application as Light Source Means for Controlling Agricultural Pests

The Ce doped Strontium Magnesium silicate phosphor Sr2MgSi2O7:Ce is compounded by using high temperature roasting process, and the plane sample of prepared phosphor is obtained by tablet press method. A modified MCJ-01A friction tester with the friction pair of glass bar against on the plane phosphor sample is used to determine the triboluminescence property of Ce doped Strontium Magnesium silicate phosphor in the linear contact sliding friction. Examination on the triboluminescence of Ce doped Strontium Magnesium silicate phosphor indicates that a quality triboluminescent phosphor with 448nm± blue spectrum emission can be obtained only in the 1200°C calcining temperature, and only 0.010 molar Ce doping concentration in the Sr2MgSi2O7:Cex can promote the prepared phosphor to generate a higher triboluminecent emission and a smaller full width at half maximum (FWHM). The suitable level of applied load is beneficial to hold a balance between wear increment and spectrum intensity. Finally a triboluminescent unit with squirrel cage structure is constructed to realize the triboluminescence of multiple glass bars against on the cylindrical phosphor in the manner of sliding friction. This can satisfy the light emitting of 360o azimuth, and generate more tribological luminous flux.

Europium doped silicate phosphors: Synthetic and characterization techniques

Europium doped silicate phosphors: Synthetic and characterization techniques

(Invited) Investigation of Eu Doped Silicate Phosphor Family M2Ln8(SiO4)6O2 (M=Mg, Ca, Sr; Ln=La, Y) with Apatite Structure for LED Applications

Research and development of new high-efficiency phosphors for white light generation using light emitting diodes (LEDs) is presently one of the most important topics for development of light sources for general and special lighting. LED light sources offer significant advantages compared to other lighting technologies: low power consumption, high efficiency, long service life, compact size, environmentally-friendly (mercury-free) modules, high resistance to external conditions [1,2]. Search for new compounds with better performance is actively going on. Silicates with apatite structures have got attention for LED phosphor applications because of their stability and high efficiency having a potential for white light generation [3-6]. The complicated crystal structure of silicate apatites provides a good basis for advanced materials engineering. There are two crystallographic sites in the IXA14 VIIA26(SiO4)6O2 structure, which can be occupied by the alkaline earth (M2+) and rare earth (Ln3+) cations, 9 and 7-fold coordinated for A1 and A2, respectively. Besides that, silicate apatites can be doped and codoped with ions of different valence states, i.e. the conditions can be realized for various energy and charge transfer processes. Variation of alkaline earth ions in a row Mg – Ca – Sr changes occupancy of the 9 and 7-fold coordinated sites due to the properties of the apatite structure [7]. Small radius Mg2+ ions tend to occupy preferentially the A2 site and larger radius Sr2+ ions mainly the A1 site resulting in IXLn4 VIILn4 VIIMg2(SiO4)6O2 and IXSr2 IXLn2 VIILn6(SiO4)6O2 compounds, respectively. Medium size Ca2+ ions follow statistical distribution of cations populating both sites. These features of silicate apatites allow advanced materials engineering providing large potential for the development of phosphors for white light generation using LEDs. The motivation of our research is twofold: firstly, the study of the silicate apatite phosphor family enables deeper understanding how structural peculiarities influence electronic properties and secondly, evaluation of application potential for the developed rare earth doped materials in the LED field. The studied phosphors, silicate apatites M2Ln8(SiO4)6O2 (where M = Mg, Ca, Sr; Ln = Y, La) doped with europium ions at various concentrations (0.5-2.0 at. %), were prepared by high-temperature solid-state reaction using the precursors synthesized under hydrothermal conditions (e.g see [8]). The selected samples were annealed in H2/Ar reducing atmosphere in order to convert Eu3+ into Eu2+ and bring more understanding between interplay of electronic subsystems of ions with different valence states. The structural and luminescence properties of synthesized phosphors were characterized by XRD analysis, Raman spectroscopy, diffuse reflectance, time-resolved photoluminescence studies (under blue-to-VUV excitation), cathodoluminescence and site-selective high resolution spectroscopy in the temperature range of 3-400 K. Particle size and morphology of the samples were investigated by scanning electron microscopy. We followed the evolution of emission spectra and decay kinetics of the phosphors under excitation of different 4f levels of Eu3+, (O2- - Eu3+) charge transfer band (peaked near 275 nm) and into host absorption (< 160 nm). Based on experimental data, several emission centers due Eu3+ and Eu2+ ions as well as for host emissions were identified. Depending on the host compound and treatment procedure the phosphors can show a large variety of spectral properties which cannot be explained in many cases as only by the presence of two crystallographic sites for doping ions. Accordingly, additional mechanisms should be also considered for the detailed explanation of the observed properties. The relaxation and energy transfer processes for silicate apatites M2Ln8(SiO4)6O2 will be discussed. Also properties relevant for LED application will be reported. This research project NANOLED # 361 was carried out within framework of the ERA.Net RUS Plus Programme supporting cooperation in 'Science & Technology' between European Union and Russia (RFBR Grant 16-52-76028 ERA_а). 1. C. Feldmann, T. Jüstel, C.R. Ronda, P.J. Schmidt, Adv. Funct. Mater. 13 (2003) 511. 2. E.F. Schubert, J.K. Kim, Science 308 (2005) 1274. 3. Y. Shen, R. Chen, G. G. Gurzadyan, J. Xu, H. Sun, K. A. Khor, Z. Dong, Opt. Mater. 34 (2012) 1155. 4. C.-H. Hsu, S. Das, C.-H. Lu, J. Electrochem. Soc. 159(2012) J193. 5. J. Sokolnicki, E. Zych, J. Lumin. 158 (2015) 65. 6. S. Yuan, L. Wang, Z. Cui, Y. Yang, H. Zeng, F. Cheviré, F. Tessier, G. Chen, J. Mater. Sci. & Appl. 1 (2015) 133. 7. G. Blasse, J. Solid State Chem. 14 (1975) 181. 8. V.N. Makhov, N.M. Khaidukov, Optics and Spectroscopy 116, (2014) 748.

Red emissive CuInS_2-based nanocrystals: a potential phosphor for warm white light-emitting diodes

We here report the integration of red emissive CuInS(2) based nanocrysals as a potential red phosphor for warm light generation. By combining red emissive CuInS(2) based nanocrysals with commercial yellow emissive YAG:Ce and green emissive Eu(2+) doped silicate phosphors, we fabricated warm white light-emitting diodes with high color rendering index up to ~92, high luminous efficiency of 45~60 lm/W and color temperature less than 4000K.

Sol–gel deposition and characterization of Mn 2+-doped silicate phosphor films

Mn 2+-doped Zn 2SiO 4 and Mg 2Gd 8(SiO 4) 6O 2 phosphor films were deposited on silicon and quartz glass substrates by sol–gel process (dip-coating). The variations of sol viscosity with time and film thickness with the number of layers were investigated in Zn 2SiO 4: Mn system. The results of XRD and IR showed that the Zn 2SiO 4: Mn films remained amorphous below 700°C and crystallized completely around 1000°C. From AFM studies, it was observed that the grains with 0.5–0.8 μm size packed closely in Zn 2SiO 4: Mn films, which were uniform and crack free. The luminescence properties of Zn 2SiO 4: Mn films were characterized by absorption, excitation and emission spectra as well as luminescence decay. These properties were discussed in detail by a comparison with those of Mn 2+ (and Pb 2+)-doped Mg 2Gd 8(SiO 4) 6O 2 phosphor films.