SiO4 Phosphors Research Articles

Energy Transfer and Temperature Measurement Performance for NaGd(1-x-y)TbxEuySiO4 Phosphor

NaGd(1-x-y)TbxEuySiO4 phosphors were synthesized through high-temperature solid-state reaction method. The effects of doping concentration and temperature of Tb3+ and Eu3+ doped NaGdSiO4 on the luminescence performance are investigated in detail. Eu3+ luminous intensity enhancement and excitation spectra expansion are realized through efficient energy transfer of Tb3+ → Eu3+. The luminous color is regulated from green to red by altering the concentration of Tb3+ and Eu3+. The temperature measurement performance of the NaGd0.85Tb0.1Eu0.05SiO4 phosphor has also been witnessed. In the temperature range of 273 K − 483 K, the maximum absolute and relative sensitivity are 0.008 K−1 and 0.533%K−1, respectively. It is evident that NaGd(1-x-y)TbxEuySiO4 phosphors are available for temperature measurement.

Photoluminescence assessment of Ba2-xEuxSiO4 phosphor prepared through a solid phase reaction technique using silica nanoparticles as a precursor

Generally, garnets-based phosphors are being employed in the Phosphor converted white emitting light (pc-WLED) technology. But the deficiency of red spectral components in them makes silicate-based phosphors to be successful. Our study reports the preparation of novel single-phased Ba2-xEux3+SiO4 phosphor obtained by varying dopant (Eu3+) concentration via simple dry solid-phase reaction method. Here, we have used silica nanoparticles as silicate precursor owing to their optical tunability and emissive properties which in turn depend on the occupancy of dopant in the cation site of crystal and morphology, A detailed analysis of the crystal phase and morphology of the silica nanoparticle assisted Ba2-xEux3+SiO4 phosphor (BSS) has been reported. To evaluate the colour output and tunability, the luminescence properties including excitation and emission spectra, asymmetric ratio and concentration quenching were also investigated. The obtained results indicate a rectangular-shaped morphology of BSS with red emission precisely peaked at 592 and 617 nm under the excitation wavelength of 280 nm. The optimum concentration for the luminescence quenching was found to be 7 mol% of Eu3+ in BSS phosphor and was successfully taken for further theoretical experimentations. The critical transfer distance was found to be 1.1 nm. The CIE colour coordinates (x, y) were calculated to be (0.63,0.36). The developed phosphor is found to be a potential candidate for providing enough emission at the red spectral region.

Distinctive features of the crystal-chemical, thermal and luminescence properties of (Zn0.94Mg0.06)2SiO4:Mn phosphor

The effect of magnesium introduction on the structural, thermal, and luminescent characteristics of Zn2SiO4:Mn at the fixed magnesium concentration of 6 at% has been studied. Zn1.88–2xMn2xMg0.12SiO4 phosphors were synthesized by the solid phase method. The structural properties were studied using X-ray diffraction. The luminescent properties were characterized by the PLE and PL spectra. The charge state of manganese ions was determined by the XPS method. It was found that the Zn1.88–2xMn2xMg0.12SiO4 samples at x ≤ 0.14 were single-phase. The unit cell parameters of the solid solutions changed nonmonotonically with increasing x. The change in the linear trend of the parameters occurred at x = 0.06, and was caused by the oxidation of a part of the Mn2+ ions to Mn3+. The introduction of 6 at% magnesium into the Zn2–2xMn2xSiO4 structure caused an inversion of the crystallographic positions in which manganese was predominantly oxidized. It was shown that the melting temperatures of the Zn2–2xMn2xSiO4 and Zn1.88–2xMn2xMg0.12SiO4 solid solutions decreased with increasing manganese concentration, but were practically independent of the presence of magnesium. The structural phase transition α→β was recorded in the premelting region for all Zn2–2xMn2xSiO4 compositions. For the Zn1.88–2xMn2xMg0.12SiO4 solid solutions, the α→β transition was registered only for x˂0.06. The optimal photoluminescence intensity of Zn2–2xMn2xSiO4 shifted to the region of lower values of x with the introduction of magnesium and turned out to be maximum for Zn1.76Mn0.12Mg0.12SiO4. The introduction of 6 at% magnesium reduced the decay time by almost a factor of two; for the sample with x = 0.06 the decay time was 0.654 ms.

Precisely control the ultraviolet to blue light conversion for plant growth: Rigid crystal structure, lattice substitution and flux effect in the Ca1.1Sr0.9SiO4:Ce3+, Li+ phosphor

A series of Ce3+-doped Ca1.1Sr0.9SiO4-based phosphors has led to the development of a fingerprint spectrum to precisely tune the UV to blue light conversion for application in the photosynthesis of different plants in agriculture. The addition of MX2 flux (M = Ca, Ba; X = Cl, Br) not only remarkably enhances the luminescence efficiency, but also fine tunes the photoluminescence (PL) wavelength and photoluminescent excitation (PLE) peaks. With increasing Al content doping in the Si site, the excitation and emission peaks of the Ca1.08Sr0.88Si1-zAlzO4:0.02Ce3+,0.02Li+,0.04CaCl2 (CSSA:CeLiCaCl) phosphor shift to longer wavelengths, i.e. from 367 (z = 0) to 373 (z = 0.04) nm and from 429 (z = 0) to 448 (z = 0.04) nm, respectively, along with an increase of the luminescence intensity. Rietveld refinement of the XRD data for Ca2-ySrySiO4 (y = 0.8, 0.9, 1.0) revealed that Ca1.1Sr0.9SiO4 has the highest rigidity, which can be correlated with the shortest Si-O bond length and strongest bond energy along the series. The crystal structure and unit cell parameters of CSSA:CeLiCaCl (z = 0, 0.03 and 0.05) were also obtained, revealing that the efficient and tunable blue emission of the CSSA:CeLiCaCl phosphors can be attributed to the crystal structure distortions induced by the [(Si/ Al)O4] tetrahedron, while high rigidity is maintained. The combined effects of the Si4+ substitution by Al3+ and flux addition on the crystal structure and luminescence properties of the Ce3+-doped Ca1.1Sr0.9SiO4 phosphors are discussed in detail.

Effect of different temperatures to remove reduction gas on the photoluminescence properties of Eu-doped Li2 (Ba1-x Srx )SiO4 phosphors.

In this study, Eu-doped Li2 (Ba1-x Srx )SiO4 powders (x = 0, 0.2, 0.4, and 0.6) were synthesized at 850°C in a reduction atmosphere (5% H2 + 95% N2 ) for a duration of 1 h using a solid-state reaction method. The reduction atmosphere was infused as the synthesis temperature reached 850°C, and was removed as the temperature dropped to 800-500°C. Li2 (Ba1-x Srx )SiO4 (or Li2 BaSiO4 ), (Ba,Sr)2 SiO4 (or BaSiO4 ), and Li4 SiO4 phases co-existed in the synthesized Eu-doped Li2 (Ba1-x Srx )SiO4 powders. A new finding was that the reduction atmosphere removing (RAR) temperature of the Li2 (Ba1-x Srx )SiO4 phosphors had a large effect on their photoluminescence excitation (PLE) and PL properties. Except for the 800°C-RAR-treated Li2 BaSiO4 phosphor, PLE spectra of all other Li2 (Ba1-x Srx )SiO4 phosphors had one broad emission band with two emission peaks centred at ~242 and ~283 nm; these PL spectra had one broad emission band with one emission peak centred at 502-514 nm. We showed that the 800°C-RAR-treated Li2 BaSiO4 phosphor emitted a red light and all other Li2 (Ba1-x Srx )SiO4 phosphors emitted a green light. Reasons for these results are discussed thoroughly.

Multisite-Occupancy-Driven Efficient Multiple Energy Transfer: A Straightforward Strategy to Achieve Single-Composition White-Light Emission in Ce3+-, Tb3+-, and Mn2+-Doped Silicate Phosphors.

It is unquestionably true that site occupation and energy transfer play important roles in the luminescent properties of optical materials from both practical applications and theoretical research. In this paper, multisite-occupancy-driven multiple energy transfers were used as a straightforward strategy to achieve single-composition white-light emission in Ce3+-, Tb3+-, and Mn2+-doped Ba1.2Ca0.8SiO4 (BCS) phosphors. The Ce3+-, Tb3+-, and Mn2+-doped T-phase orthosilicate BCS samples were synthesized by traditional solid-state reactions. The phase composition was checked via X-ray diffraction (XRD), and the luminescent properties were systematically studied by photoluminescence spectroscopy and fluorescence decay curves. A detailed study on the efficient and multiple energy transfers of Ce I → Mn2+, Ce II → Tb3+, and Ce II → Tb3+ → Mn2+ was carried out. Satisfactorily, the selected phosphor exhibits a high internal quantum efficiency (QE) of 81% and good thermal stability. In addition, an evident negative thermal quenching phenomenon, i.e., the emission intensity increases with increasing temperature, is provided. Moreover, the mechanism of negative thermal quenching was proposed. On the basis of these excellent luminescence properties, a white LED with color-rendering index (Ra = 89) was fabricated by integrating the phosphor on an n-UV 365 nm chip. These results show that the materials present potential application in the field of phosphor-converted white LEDs.

Realization of color tunable via energy transfer in Ba1.2Ca0.8SiO4:Tb3+, Mn2+ phosphor

A detailed investigation on photoluminescence properties and energy transfer mechanism of Tb3+/Mn2+ singly doped and co-doped T-phase orthosilicate Ba1.2Ca0.8SiO4 (BCS) phosphors, synthesized by conventional solid state reaction, is provided. All the samples were investigated by X-ray diffraction (XRD), photoluminescence spectroscopy and fluorescence decay curve. The Mn2+ emission intensity of BCS:Tb3+, Mn2+ is 28 times stronger than that of BCS:Mn2+. In addition, the emission color of BCS:Tb3+, Mn2+ phosphors can be tuned from green to orange-red by varying Mn2+ concentration. The efficient energy transfer from Tb3+ to Mn2+ is responsible for these phenomena. By employing the Inokuti–Hirayama model and Dexter's energy transfer theory, the dipole–dipole interaction is confirmed as the predominant multipolar effect in controlling this energy transfer process.

Efficient energy transfer induced tunable emission in Ce3+ and Eu2+ co-doped Ba1.2Ca0.8SiO4 phosphor

A series of Ce3+ and/or Eu2+ doped T-phase orthosilicate Ba1.2Ca0.8SiO4 (BCS) phosphors were synthesized by conventional solid state reaction. The as-synthesized samples were investigated by X-ray diffraction (XRD), photoluminescence spectroscopy, and fluorescence decay curve. The red shifts of emission peak were observed in Ce3+ and/or Eu2+ doped BCS phosphors. The possible rationalization for the red shift was discussed. The emission color for BCS:Ce3+, Eu2+ phosphors can be turned from deep blue to bluish green by varying Eu2+ concentration. The efficient energy transfer from Ce3+ to Eu2+ is responsible for this phenomenon. The energy transfer mechanism was validated and demonstrated to be a resonant type via a dipole–dipole interaction by using Inokuti–Hirayama model and Dexter's energy transfer theory. In addition, the thermal stability of the phosphors is also investigated. Furthermore, the quantum efficiency (QE) of Ba1.15Ca0.8SiO4:0.02Ce3+, 0.02Na+, 0.01Eu2+ phosphor was found to be 38.77%. Finally, to explore the practical applications of obtained compounds for indoor illumination, a white light-emitting-diode (LED) device which contained a n-UV chip, prepared phosphors, and green emitting and red emitting phosphors was packaged. The packaged white LEDs device can emit dazzling white light with satisfied color coordinate of (0.350, 0.335), Ra (84), and correlated color temperature (4744 K).

Microwave-assisted sintering synthesis of greenish-yellow emitting Sr2 SiO4 :Eu2+ phosphors.

Europium ion (Eu2+ ) doped Sr2 SiO4 phosphors with greenish-yellow emission were synthesized using microwave-assisted sintering. The phase structure and photoluminescence (PL) properties of the obtained phosphor samples were investigated. The PL excitation spectra of the Sr2 SiO4 :Eu2+ phosphors exhibited a broad band in the range of 260nm to 485nm with a maximum at 361nm attributed to the 5f-4d allowed transition of the Eu2+ ions. Under an excitation at 361nm, the Sr2 SiO4 :Eu2+ phosphor exhibited a greenish-yellow emission peak at 541nm with an International-Commission-on-Illumination (CIE) chromaticity of (0.3064, 0.4772). The results suggest that the microwave-assisted sintering method is promising for the synthesis of phosphors owing to the decreased sintering time without the use of additional reductive agents.

On the photoluminescence of multi-sites Ce3+ in T-phase orthosilicate and energy transfer from Ce3+ to Tb3+

Ce3+, Tb3+ co-doped T-phase orthosilicate Ba1.2Ca0.8SiO4 phosphors were prepared by means of solid state reactions. The synthesized samples were investigated using XRD and PL emission and excitation spectra. The emission spectra for Ce3+ doped Ba1.2Ca0.8SiO4 phosphors show broad bands in the 320–550 nm spectral region. The excitation spectra exhibit several absorption peaks in the range of 250–400 nm. Both the emission and excitation spectra are dependent on the excitation or monitoring wavelengths. We attribute these results to Ce3+ ions occupying two different crystallographic sites (i.e., Ce I and Ce II). The Ce3+, Tb3+ co-doped Ba1.2Ca0.8SiO4 phosphors show Tb3+-related line emissions in the 475–600 nm spectral region and Ce3+-related band emissions in the 350–525 nm spectral region when the 4f → 5d transition of Ce3+ is excited (λex = 345 nm), indicating that energy transfer from Ce3+ to Tb3+ takes place. Moreover, the emission intensity of 5D4 → 7F5 transition for Ba1.00Ce0.02Tb0.08Li0.10Ca0.8SiO4 is 30 times stronger than that of Ba1.04Tb0.08Li0.08Ca0.8SiO4 sample under 345-nm UV excitation.

Chemical unit cosubstitution and tuning of photoluminescence in Eu2+ doped Ca1.65-xScxSr0.35Si1-xGaxO4 phosphors

The design scheme of chemical cosubstitution of [Sc3+- Ga3+] for [Ca2+-Si4+] pairs in the Eu2+ doped Ca1.65Sr0.35SiO4(CSSO) phosphors has been put into practice to investigate their structure and optical properties systematically. X-ray diffraction patterns and Rietveld refinements were used to demonstrate the successful incorporation of Sc3+/Ga3+ into CSSO: Eu2+. All phosphors exhibit the general orthorhombic structure with space group of P21CN. Eu2+ activated CSSO phosphors exhibit strong absorption in the range of 260–450 nm and a green emission peak centered at about 506 nm. Under the excitation of 365 nm, the peak position for the Sc-Ga substitutions can be shifted from 506 to 524 nm, which is expected to obtain single-phased phosphors excited by UV-LEDs. The cosubstitution of [Sc3+- Ga3+] for [Ca2+-Si4+] can improve the thermal stability of the materials. This research is in favor of enriching colors of Eu2+ doped CSSO phosphors.

Optical characterization of Eu3+ doped MLSiO4 (M = Ca, Sr, Ba and L = Mg) phosphor materials for display devices

Mixed metal oxide based phosphors of Eu3+ doped MLSiO4 (M = Ca, Sr, Ba and L = Mg) type were explored using sol–gel process. Optical characteristics of different compositions of calcium magnesium silicate including CaMg(0.97)SiO4, Ca(0.97)MgSiO4 and Ca(0.985)Mg(0.985)SiO4 phosphor materials were investigated in detail prepared with 0.03 molar concentration of europium ion. Emission spectra of these materials presented dominant peak at 613 nm because of electric dipole (5D0 → 7F2) transition of Eu3+ ion. Red luminescence in the silicate phosphors was due to the presence of Eu3+ ion in their lattice. Effect of variation of metal ion (M = Ca, Sr and Ba) on the optical properties of MLSiO4 (L = Mg) materials was also explained in the present report. Particle size of the prepared materials was computed using Debye Scherrer’s equation from X-ray diffraction analysis. Different crystal structures were examined from diffraction pattern available for these materials. Chemical structure as well as bonding present in these phosphor materials was analyzed from Fourier Transform Infrared study. Microscopic tool including transmission electron microscope was applied to approximate the particle size of prepared materials. Excellent photoluminescence response and nanosize of these materials made them suitable in display device technology.

Photoluminescence Properties of Red-Emitting Ca3ZrSi2O9:Eu2+ Phosphors

It has been well-known that silicon-based nitride phosphors such as CaAlSiN3:Eu2+ and Sr2Si5N8:Eu2+ possess excellent red-light emission when excited by blue-light region. However, preparation of such silicon-based nitride phosphors in pure form should be needed to sinter precursor powders under high pressure and temperature conditions. On the contrary, Eu2+-activated silicates with alkaline earth ions have been reported as high efficient phosphors. Such silicon-based oxide phosphors in pure form can be easily obtained by simple preparation techniques without any critical conditions mentioned above. Therefore, productivity and production cost for silicate phosphors are advantageous for the commercial production of red phosphors. We have reported red-emitting Ca1.2Eu0.8SiO4 phosphors excited by blue light region.1) The wavelength at the maximum emission of Ca1.2Eu0.8SiO4 phosphors was 650nm.1) We have recently discovered new red-emitting Ca3ZrSi2O9:Eu2+ phosphors with high Eu2+ concentration excited by near-UV and blue-light region. Ca3ZrSi2O9 activated by low Eu2+ concentrations (Eu2+: 1 mol%) exhibited a green emission at 530 nm. However, with increasing Eu2+ concentration to 10 mol%, Ca3ZrSi2O9:Eu2+ phosphors exhibited red emission peaking at 650 nm while the green emission disappeared. Based on the crystal structure data of Ca3ZrSi2O9, there were three Ca sites in Ca3ZrSi2O9, where Eu2+ ions were occupied.2) Two of the Ca sites were smaller than another Ca site. We presume that emission at 530 nm from Eu2+ occupying the large Ca site was not observed owing to Eu2+ concentration quenching, as well as reabsorption of the green emission light from Eu2+ at the large Ca site by Eu2+ at the two small Ca sites. Thus, the deep-red emission of Ca3ZrSi2O9:Eu2+ phosphors observed is considered to be emission from Eu2+occupying these small Ca sites. 1) Y. Sato, H. Kato M. Kobayashi, T Masaki, D. H. Yoon and M. Kakihana, Angew. Chem. Int. Ed. 53(2014) 7756. 2) J. R. Plaister, J. Jansen, R. G. de Graaff, D. J. W. IJdo, J. Solid State Chem. 115 (1995) 464.

Photoluminescence and afterglow of Mn2+ doped lithium zinc silicate

Novel green emitting long lasting phosphorescence (LLP) Li1.14Zn1.43SiO4:Mn2+ (LZS: Mn2+) was prepared successfully through a conventional solid-state reaction. Phase purity was checked by X-ray diffraction. The photoluminescence and afterglow properties of as-prepared phosphors were studied systematically by diffuse reflectance spectra, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence glow curves measurements. The photoluminescence spectra and LLP spectra indicated that LZS: Mn2+ phosphors exhibits green emission center at 526nm originated from 4T1→6A1 transition of Mn2+. The duration of Mn2+ doped Li1.14Zn1.43SiO4 phosphors can last about 1h. Thermoluminescence glow curves indicated that the LLP of LZS: Mn2+ phosphor was generated by the suitable trap depth. Based on the experimental results, a model was constructed to discuss the mechanism of afterglow briefly.

Preparation and characterization of a green emitting Li2Ca0.4Sr0.6SiO4:Tb3+ phosphor with afterglow behavior

A novel green emitting long afterglow phosphor Li2Ca0.4Sr0.6SiO4:Tb3+ was obtained via a high temperature solid-state reaction in air atmosphere. X-ray diffraction (XRD), photoluminescence spectroscope (PLS), long afterglow spectroscope (LAS) and thermal luminescence spectroscope (TLS) were performed to characterize the physical properties of the phosphors. Typical 5D4-7Fj transitions of Tb3+ ions were detected by PL spectra, corresponding to CIE chromaticity coordinates of x =0.3456, y =0.5745. An optimal concentration of Tb3+ in the substrate was determined as 0.8at%. The Li2Ca0.4Sr0.6SiO4 phosphors showed a typical afterglow behavior when the UV source was switched off. A typical triple exponential decay behavior was confirmed after fitting the experimental data. Thermal simulated luminescence study further indicated that the afterglow behavior of Li2Ca0.4Sr0.6SiO4:Tb3+ phosphors was generated by the recombination of electrons with the holes resulted from the doping of rare-earth ions (Tb3+) in Li2Ca0.4Sr0.6SiO4 host. The long afterglow luminescence mechanism of Li2Ca0.4Sr0.6SiO4:Tb3+ is illustrated and discussed in detail on the basis of experimental results.

Luminescence enhancement of (Sr1-x Mx )2 SiO4 :Eu2+ phosphors with M (Ca2+ /Zn2+ ) partial substitution for white light-emitting diodes.

Eu2+ -doped Sr2 SiO4 phosphor with Ca2+ /Zn2+ substitution, (Sr1-x Mx )2 SiO4 :Eu2+ (M=Ca, Zn), was prepared using a high-temperature solid-state reaction method. The structure and luminescence properties of Ca2+ /Zn2+ partially substituted Sr2 SiO4 :Eu2+ phosphors were investigated in detail. With Ca2+ or Zn2+ added to the silicate host, the crystal phase could be transformed between the α-form and the β-form of the Sr2 SiO4 structure. Under UV excitation at 367nm, all samples exhibit a broad band emission from 420 to 680nm due to the 4f6 5d1 →4f7 transition of Eu2+ ions. The broad emission band consists of two peaks at 482 and 547nm, which correspond to Eu2+ ions occupying the ten-fold oxygen-coordinated Sr.(I) site and the nine-fold oxygen-coordinated Sr.(II) site, respectively. The luminescence properties, including the intensity and lifetime of Sr2 SiO4 :Eu2+ phosphors, improved remarkably on Ca2+ /Zn2+ addition, and promote its application in white light-emitting diodes. Copyright © 2016 John Wiley & Sons, Ltd.

Anomalous Orange Light-Emitting (Sr,Ba)2SiO4:Eu(2+) Phosphors for Warm White LEDs.

Phosphors with sufficient red emission component are necessary for warm white light-emitting diodes. In this work on (Sr,Ba)2(1-x)Eu2xSiO4 phosphors, (Sr,Ba)1.5Eu0.5SiO4 achieved 75% of an internal quantum efficiency under excitation by blue light. Surprisingly, the (Sr,Ba)1.5Eu0.5SiO4 exhibited orange emission, against the well-known traditional green-yellow emission of (Sr,Ba)2SiO4:Eu(2+). Moreover, the concentration quenching of Eu(2+) in (Sr,Ba)2SiO4 was abnormally unobvious. With the help of calculations based on the density functional theory, it was discovered that the distinct local environment of luminescence centers rather than usual explanation such as self-absorption or intensified crystal field splitting, is responsible to the interesting red shifts in excitation and emission spectra. The refinement analysis based on X-ray diffraction revealed that the unequal distribution of Eu(2+) to two crystallographic sites caused low concentration of Eu(2+) at the 9-coordination site, inhibiting the concentration quenching. The (Sr,Ba)1.5Eu0.5SiO4 phosphor has warmer emission than the commercial Y3Al5O12:Ce(3+). This study also promotes research on the effect of site occupancy and the local environment of luminescence centers.

Luminescence properties of Eu2+ in T–phase Ba1.3Ca0.7SiO4 lattice from multiple crystallographic sites at different temperatures

Eu2+–activated Ba1.3Ca0.7SiO4 phosphor has been synthesized by high temperature solid state reaction method. The optical properties of (Ba1.29Eu0.01)Ca0.7SiO4 are investigated using photoluminescence (PL), photoluminescence excitation (PLE) spectra and luminescence decay time measurement between 10 and 523 K. The blue emission band peaking at ∼448 nm is observed to be asymmetric. It can be divided into three Gaussian bands with maxima at ∼440 (Eu I), ∼464 (Eu II) and ∼503 nm (Eu III), which is in good agreement with that measured from low temperature at 10 K. The temperature dependence of the PL intensity is also measured. The thermal quenching of Ba1.3Ca0.7SiO4:Eu2+ is about 235 °C. The PL decay times of 425, 455 and 570 nm emission at 10 K are 0.23, 0.28 and 1.00 μs. They can be attributed to the lifetimes of Eu I, Eu II and Eu III site, respectively. The decay times of the 425 and 455 nm emission almost remain constant at 10 K and 523 K. The decay times of the emission at 570 nm do not change a lot with increasing temperature up to 300 K, then decrease to 0.2 μs at 523 K Ba1.3Ca0.7SiO4:Eu2+ is a candidate blue-emitting phosphor for white LEDs.

Photoluminescence Properties of Efficient Blue-Emitting Phosphor α-Ca1.65Sr0.35SiO4:Ce(3+): Color Tuning via the Substitutions of Si by Al/Ga/B.

A series of Ce(3+)-doped α-Ca1.65Sr0.35SiO4 (CSSO) phosphors without and with the substitutions of Si by Al/Ga/B were synthesized via the high-temperature solid-state reaction process. X-ray diffraction patterns and Rietveld refinements were used to demonstrate the successful incorporations of Al/Ga/B into CSSO:Ce(3+). Without Al/Ga/B, the Ce(3+) singly doped CSSO phosphors present intense blue emission, which correspond to the broad emission bands in visible region with the wavelength range from 360 to 580 nm upon 350 nm excitation. The optimal emission intensity occurs in CSSO:0.05Ce(3+) sample with the emission peak wavelength at 436 nm. With the introduction of Al/Ga/B into the CSSO:0.05Ce(3+), the emission peak shifts from 436 to 457/465/446 nm under 365 nm excitation, respectively. The red shift of Ce(3+) emission is attributed to the polyhedral distortion of the cations, resulting in the enhancement of crystal field spitting due to the variations of the adjacent (Al/Ga/B,Si)O4 polyhedron. Moreover, the temperature-dependent photoluminescence was determined to be of light impact to CSSO:Ce(3+) with the introduction of Al/Ga/B. This research is useful for enriching the emission colors of Ce(3+)-activated phosphors.

Structure, Crystallographic Sites, and Tunable Luminescence Properties of Eu(2+) and Ce(3+)/Li(+)-Activated Ca1.65Sr0.35SiO4 Phosphors.

Eu(2+) and Ce(3+)/Li(+) singly doped and Eu(2+)/Ce(3+)/Li(+)-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the αL′-Ca2SiO4 phase with the Sr addition into Ca2SiO4, and the preferred crystallographic positions of the Eu(2+) and Ce(3+)/Li(+) ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2–x)Sr(x)SiO4 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce(3+)/Li(+) singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in the range of 250–450 nm and a blue emission peak centered at about 465 nm. When Eu(2+) ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce(3+) to Eu(2+). The involved energy-transfer process between Ce(3+) and Eu(2+) and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs).