Single Phosphor Research Articles

ZnGa2–yAlyO4:Mn2+,Mn4+ Thermochromic Phosphors: Valence State Control and Optical Temperature Sensing

Dual-emitting and thermochromic manganese ion single doped ZnGa2-yAlyO4 phosphors were prepared by solid-state reaction. The regulation of the valence state and the luminescent properties, especially the luminescent thermal stability of manganese ions in ZnGa2-yAlyO4, are discussed in detail. When excited by ultraviolet (UV) light, the emission spectra of ZnGa2O4:Mn2+,Mn4+ present an ultranarrow green emission band at 503 nm with a fwhm of 22 nm, which derives from the Mn2+ ions formed by the self-reduction of doped Mn4+, and a red emission band of the Mn4+ ions at 669 nm. In addition, a ZnGa2-yAlyO4:Mn2+,Mn4+ solid solution was designed and synthesized by Al3+ replacing Ga3+. The doping of Al3+ effectively inhibited the degree of Mn4+ self-reduction to Mn2+, thus realizing the regulation of valence state of manganese ions. Interestingly, the thermal stability of luminescence shows that the response of Mn2+ and Mn4+ to temperature is obviously different in ZnGa2-yAlyO4, implying the potential of the prepared phosphors as optical thermometers. Subsequently, three kinds of optical thermometers with superior color discrimination and high relative sensitivity (Sr) based on the fluorescence intensity ratio (FIR) technique were realized in 100-475 K. The Sr value of ZGO:0.005Mn/ZGA0.5O:0.005Mn/ZGAO:0.005Mn phosphors can be as high as 4.345%/4.001%/3.488% K-1 (at 350/325/400 K), reflecting the great potential of ZnGa2O4:Mn2+,Mn4+ for optical thermometry applications.

Y2O3:Ho3+ and ZnO:Bi3+: a selection for enhancing color quality and luminous flux of WLEDs

As the luminescence industry develops, the white light light-emitting diode (LED) package with a single chip and a single phosphor although produces good luminous flux but has a poor color rendering index (CRI) can no longer fulfill the requirements of modern lighting applications. Therefore, this research is conducted to response to the urgent demands of improving other lighting qualities of WLED while maintaining high luminous efficiency. To achieve this target, we applied the new WLED package, which contains multi-chips and multi-phosphor layers, and have obtained outstanding results in both CRI and luminous efficacy. Two types of phosphor used in the WLED package are Y2O3:Ho3+ and ZnO:Bi3+. A color configuration model is also developed to adjust the shading of the white-light LED module. The results of this research show that the triple-layer phosphorhas the best performance when applied in a white-light LED package, which is demonstrated through better color quality, CRI and luminous efficacy, The manufacturers can rely on this research to produce the optimal-quality WLED, or WLED that is appropriate to their quality demands.

Transmission Geometry Laser Lighting with a Compact Emitter

Laser lighting systems can take many form factors for applications, such as spotlighting, general illumination, or decorative lighting. The use of lasers in conjunction with phosphors for white lighting leads to questions about incorporating the various package elements. Some practical considerations of a transmission geometry system implementing a blue laser and a yellow Ce:YAG single crystal phosphor are discussed, with specific focus on color tuning and the optical efficiency of the single crystal. A compact emitter is demonstrated with examples of modifications to increase the system performance and complexity. Moving from a cool white system to a warm white system is done through the addition of a red light such as a red laser or red phosphor. The single crystal phosphor component needs to allow light to be coupled in from the laser and has high extraction efficiency. A wavelength‐selective reflective coating is implemented to address these concerns, which increases the luminous efficacy of the system. Engineering the phosphor element using this concept may allow for single crystal phosphors to be viable options for future laser lighting systems.

A blue and Red Bicolor Emission Phosphor Excited by a Single n-UV and Its Self-reduction of Eu3+ → Eu2+ in Na2Al2B2O7

It has great significance to find a path on generating multicolor with one n-UV chip coated with single phosphor. Herein, Eu doped Na2Al2B2O7 (NAB) phosphor is synthesized by solid state reaction in air atmosphere. Both 4f65d1 → 4f7 transitions of Eu2+ (445 nm) and f–f transitions as 5D0 → 7FJ (J = 0, 1, and 2) of Eu3+ (570–650 nm) have been observed. When increasing Eu doping concentration, both the luminescence intensity and lifetime of Eu3+ are increased and no obvious concentration quenching is observed, while the emission strength of Eu2+ does not change monotonically but with two remarkable peak values. The optimum doping concentration of Eu is 16%. Furthermore, Eu3+ is determined to be from Eu(BO3) matrix itself, and Eu2+ testified by ESR and XPS is created by self-reduction of Eu3+ to Eu2+ in NAB due to charge compensation. When x ≥ 0.16, the Eu3+ ion would rather bond with BO3 triangles in Eu(BO3) than stay as Eu2+ in AlO4 tetrahedral in NAB. Furthermore, the as prepared sample shows an excellent thermal stability and the PL quantum efficiencies of NAB: 0.16Eu sample excited by 341 nm and 393 nm are 11.99% and 9.39%, respectively. Additionally, the calculated CIE chromaticity coordinates signify that a couple of colors can be generated by adjusting the excitation wavelength owing to the strength changes between blue and red emissions. Therefore, this novel bicolor phosphor can serve as a potential candidate for w-LEDs applications.

Multicolor emission leading by energy transfer between Dy3+ and Eu3+ in wolframite InNbTiO6

Exploring new color-tunable phosphors is of significance for light-emitting applications. In this work, multicolor-emitting InNbTiO6:Dy3+,Eu3+ phosphors were formulated and synthesized using the classic solid-state reaction technique. Phase identification indicates the pure wolframite crystal structure of as-prepared samples. According to the Rietveld refinement, dopants have been confirmed to occupy the In3+ site in the InNbTiO6 matrix. The phosphors exhibit strong absorption around 385 and 394 nm, due to the dominated transitions of 4F9/2->6H13/2 in Dy3+ and 5D0->7F2 in Eu3+, respectively, well matching the emissions from the commercial UV LED chips. In single doped phosphors, activators Dy3+ and Eu3+ under the UV light excitation respectively present their unique emission lines. As for the codoped phosphors, the co-activation and sensitization between Dy3+ and Eu3+ have been elucidated under a 394 nm excitation. The addition of Eu3+ into InNbTiO6:0.06Dy phosphor leads to the emission tuning from grass-green to orange-red crossing the warm-white region. The energy transfer can be proved through analyzing the PLE and PL profiles of the co-activated phosphors and evaluating the decay process for Dy3+ ions. According to the Dexter's theory and Reisfield's approximation, the mechanism of coupling effect has been identified to be the electric d-d (dipole-dipole) interaction. When the sum of dopants concentration equals to 0.09, the energy transfer efficiency reaches the maximum value 40.5. Moreover, the thermal stability of a representative InNbTiO6:0.06Dy3+,0.015Eu3+ phosphor have been investigated, which presented and a emission intensity maintenance of 42% at 423 K relative to room temperature 298 K. Besides, the quantum yields of InNbTiO6:0.06Dy3+, 0.04Eu3+ within the luminescence range 603–620 nm are measured to be 33.4% under the ultraviolet radiation of 394 nm. These results demonstrate that these new type phosphors have promising applications in UV LED based white light-emitting devices.

Enhancing the CRI and lumen output for the 6600 K WLED with convex-dual-layer remote phosphor geometry by applying red-emitting MGSR3SI2O8:EU2+,MN2+ phosphor

The traditional white LED product established with a single chip and a single phosphor results in a low color rendering index (CRI). The upgrade of LED package is comprised of two chips and one phosphor material and gives the higher CRI while keeping high luminous efficiency. Based on previous findings, the research paper performs the application of the two chips and two phosphors to enhance the color tunability of LEDs with different amounts and intensities of the two employed phosphors. Additionally, a color design model is built to serve the purpose of bettering the color fine-tuning of the white-light LED module. The maximum value of the difference between the measured CIE 1931 color coordinates and that of the simulated model is approximately 0.0063 around the 6600 K correlated color temperature (CCT). From the results, this study offers a quick approach to achieve the color fine tuning of a white-light LED module with a high CRI and luminous efficiency.

Improved deep red emission of Ca2LaTaO6:Mn4+ by codoping Dy3+

Mn4+ and/or Dy3+ doped Ca2LaTaO6 phosphors were prepared by a molten salt process. The phase and photoluminescence characteristics of the prepared phosphors were researched. The XRD patterns of the prepared phosphors coincide with the normative XRD pattern of Ca2LaTaO6, demonstrating that Mn4+ and Dy3+ ions doped into Ca2LaTaO6 host and formed solid solution with a single phase. For Dy3+ single doped Ca2LaTaO6 phosphors, they exhibit photoluminescence bands corresponding to 4F9/2 → 6H15/2, 6H13/2 and 6H11/2 transitions of Dy3+ while they are excited at 375 nm. For Mn4+ single doped Ca2LaTaO6 phosphors, they exhibit photoluminescence bands corresponding to 2Eg → 4A2g transitions of Mn4+ while they are excited at 321 nm Ca2LaTaO6:Mn4+/Dy3+ phosphors exhibit photoluminescence bands corresponding to transitions of Dy3+ and Mn4+ while they are excited at 375 nm. In Mn4+/Dy3+ codoped Ca2LaTaO6 phosphors, energy transfer from Dy3+ to Mn4+ occurred, which leads to the enhancements of Mn4+ photoluminescence.

A novel bifunctional Dy3+ activated RbCaF3 single phase phosphor: Facile synthesis and dual-luminescence properties for WLEDs and dosimetry applications

A series of Dy3+ activated RbCaF3 phosphors was synthesized by the conventional high temperature solid state reaction technique under ambient atmosphere. The structural properties and morphology of synthesized compounds were analyzed by PXRD and FE-SEM, respectively. The chemical composition of synthesized phosphors was obtained by EDAX. The phosphor was excited at 386 nm and monitored at 484 and 574 nm, and the strongest peak was located at 484 nm (blue region). In addition, the point of RbCaF3:Dy3+ with calculated chromaticity coordinates in the CIE diagram was located in the yellow region. TL characteristics of the RbCaF3:Dy3+ phosphor was analyzed and the glow curve peak was emitted at 355 K. The symmetry factor, Balarin parameter, activation energy and frequency factor were calculated by Chen method from the TL glow curve, and the TL signal degradation was also analyzed.

Tuning the oxidation states of dopants in Li2SrSiO4:Eu,Ce and control of the photoemission color

A color-tunable phosphor Li2SrSiO4:Eu2+,Eu3+,Ce3+ (LSSO:Eu2+,Eu3+,Ce3+) was synthesized by solid state reaction in reducing atmosphere followed by a controlled heating in air at different temperatures. Due to the different sensitivities to oxidation of the Eu2+ and Ce3+ ions, the emission centers Eu2+/Eu3+/Ce3+ can coexist in the Li2SrSiO4 host and enable a tunable coloration of the “blue-yellow-red” photoemission. By controling the energy transfer between the different activators, a single phase white phosphor was obtained.

Effective Sensitization of Eu3+ with Ce3+ by suppression of metal-to-metal charge transfer in composite structured TbF3 fluoride particles

Sensitization of Eu3+ with Ce3+ suffers from low emission intensities due to the well-known metal-to-metal charge transfer (MMCT), which effectively quenches the luminescence process. By separating sensitizer and activator spatially, reduced MMCT quenching and thus higher luminescence intensities can be expected. We chose TbF3 as host material, since it is well-known that Tb3+ acts as a mediator in the energy transfer (ET) between Ce3+ and Eu3+. Respective phosphor particles were prepared via precipitation synthesis. X-ray powder diffraction was used to determine the phase purity of the synthesized samples. Emission spectra, excitation spectra and diffuse reflectance spectra were measured to record the photoluminescence properties. Fluorescence lifetime measurements were performed to contrast the decay behavior between the co-doped and the composite approach. Especially by comparison of the emission spectra between the composite particles and the single co-doped phosphor particles it could be demonstrated that the composite approach significantly increases the luminescence intensities due to the spatial separation of Ce3+ and Eu3+.

New full color emitting phosphor through energy transfer in Bi3+ and Eu3+ co-doped La3TaO7 weberite system

A new full color emitting single phase phosphor in Bi3+ and Eu3+ ion co-doped La3TaO7 weberite system was developed via a conventional high temperature ceramic method. Phase, structural and luminescence characteristics of the developed phosphor were evaluated with different concentrations of Bi3+ and Eu3+ ions. The structural studies show that the samples are crystallized into orthorhombic weberite type structure with Cmcm space group. Photoluminescence studies reveal that the Bi3+ and Eu3+ ions co-doped La3TaO7 phosphors show broad excitations in the n-UV region (270 nm, 336 nm, 394 nm), and displays broad bluish-green emission due to the 1S0 to 3P1 and 1P1 transitions of Bi3+ and intense orange-red emission due to 5D0 to 7F0-2 transitions of Eu3+ leading to cover the whole visible spectral region. The lifetime measurements and the overlap of the spectral regions with the variation of Eu3+ concentration with Bi3+ suggest an effective energy transfer from Bi3+ to Eu3+, allowing to fine tune the chromaticity coordinates close to the white point. Further, the energy transfer mechanism existing in this phosphor is established, and it is found to be due to the dipole–quadrupole interaction. These properties make it an irrefutable candidate for single phase phosphor material for WLED application.

Controllable hydrothermal synthesis and morphology evolution of Zn4B6O13:Tb/Eu phosphors with tunable luminescent properties

A series of Tb, Eu single or co-doped Zn4B6O13 phosphors with tetrahedral morphology were synthesized by facile hydrothermal method. The influences of reaction temperature and the pH value of the reaction system on the structures and compositions of product were also investigated, in which four kinds of zinc borates with different structures and compositions (Zn4B2O7·H2O, Zn4B6O13, Zn(H2O)B2O4·0.12H2O, and H(Zn6O2(BO3)3)) were obtained. A possible growth mechanism of tetrahedral morphology of Zn4B6O13 has been proposed according to reaction time. The obtained samples were characterized by XRD, EDS, SEM, TEM, XPS, BET, DR, PL and QY. XPS results indicate that Eu2+ and Tb4+ are present in Tb/Eu co-doped Zn4B6O13, which might be generated from charge transfer between Tb3+ and Eu3+. The PL results shows that Eu3+, Tb3+ ion single-doped Zn4B6O13 microstructure exhibit orange and green emission under ultraviolet excitation, respectively. Compared to Eu3+ and Tb3+ single doped Zn4B6O13 phosphors, the Eu/Tb co-doped Zn4B6O13 phosphors showed stronger blue emission of Eu2+. These results imply that the tetrahedral morphology of Eu3+, Tb3+ ion single-doped and Eu2+/3+/Tb3+/4+ co-doped Zn4B6O13 phosphors have the promise application for nano/micro-optical functional devices.

Achieving white-light/tunable emissions via the controllable energy transfer in the single Ba9La2Si6O24:Eu3+,Bi3+ phosphor for UV converted white LEDs

Nowadays, ultraviolet (UV) and blue converted phosphors have played a key role in the solid-state lighting field, and the white light is usually produced by mixing multiple phosphors. In this work, we report a type of UV converted single white phosphor, i.e., Ba9La2Si6O24:Eu3+,Bi3+.Various techniques, such as powder X-ray diffraction (XRD), scanning electron microscopic (SEM), photoluminescence (PL) spectra, and quantum efficiency (QE), have been used to characterize the samples. In Bi3+ doped samples, upon excitation within the wavelength range of 250–380 nm can lead to three Bi3+ emission bands (i.e., 358 nm, 415 nm, and 516 nm), but only one emission band peaking at 415 nm appears when the excitation wavelength exceeds 380 nm. Structural analysis and discussion on the PL intensity variation reveal there are three Bi3+ luminescent centers at two different La3+ sites and one Ba2+ site. The Bi3+ concentration-induced luminescent quenching is dominated by the d-d interaction. In view of the spectral overlap between the Bi3+ emissions and the Eu3+ excitation spectra, the energy transfer from Bi3+ to Eu3+ of the Ba9La2Si6O24:Eu3+,Bi3+ is studied, and it is dominated by a dipole-quadrupole (d-q) interaction. Moreover, upon excitation at 365 nm, the emissions broadly tuning from blue, white and to red are achieved by varying the Eu3+ content. For the white Ba9La2Si6O24:Eu3+,Bi3+ sample, high temperature PL results show that it does not have severe degradation of emission intensity after increasing the temperature from 25 to 300 °C, exhibiting a good thermal stability. To show the potential application in the lighting fields, we fabricate a white light LEDs device by depositing this white phosphor on a 365 nm UV LED chip. As a result, the values, i.e., a color rendering index (CRI) of 95, luminous efficiency of 80 lm/W, and color temperature (CT) of ~4215 K at chromaticity (0.382, 0.398), are achieved.

Current Situation and Trend of the Phosphors for Full Spectrum LED Lighting

With the increase of the requirements for lighting quality, full spectrum light emitting diode (LED) lighting becomes the development hotspot. In this paper, the key materials for full spectrum LED phosphors are discussed and compared in detail. The advantages and disadvantages, research progress, and practical application of various color phosphors excited by violet and near ultraviolet light are emphasized, and then the existing problems, development trend, and industrial direction in this field are analyzed and prospected. Currently, there remain many problems in the phosphors excited by violet and near ultraviolet light, which can be applied in full spectrum. For example, the blue and cyan phosphors take on narrow emission spectrum, low light efficiency, and poor thermal stability; yellow phosphors and far-red phosphors have a low luminous efficiency due to their low absorption of violet or near ultraviolet light; and single matrix white phosphors have insufficient red light emission. Among them, luminous efficiency and thermal stability are the key factors restricting the application of the phosphors. Therefore, it is urgent to research the preparation and application technology of wide spectrum blue, cyan, yellow green, yellow, far-red, and single matrix white phosphors with high light efficiency and thermal stability, and develop the high-efficient and continuous preparation technology of the present phosphor products, to promote the further development of full spectrum LED.

Morphology formation mechanism and fluorescence properties of nano-phosphor YPO4:Sm3+ excited by near-ultraviolet light

A series of YPO4:Sm3+ phosphors were prepared by the hydrothermal method. The composition, structure, morphology and luminescence properties of the samples were characterized and analyzed by means of X-ray diffractometer (XRD), scanning electron microscopy (SEM and EDS) and fluorescence spectrophotometer (FL). The morphology formation mechanism and fluorescence temperature characteristic of nano-phosphor YPO4:Sm3+ were mainly studied. The results show that the products are single tetragonal phosphor yttrium ore structure with nanosphere morphology. Morphology formation mechanism of YPO4:Sm3+ is nucleation - dissolution - recrystallization - crystal growth. The strongest excitation spectrum appears at 404 nm, which belongs to the 6H5/2 → 4F7/2 transition of Sm3+. The strongest emission spectrum appears at 603 nm, which belongs to the 4G5/2 → 6H7/2 transition of Sm3+. The chromaticity coordinates show that the phosphors are red. The optimum doping concentration of activator Sm3+ in YPO4 matrix is 2%. When the doping concentration of Sm3+ is higher than 2%, concentration quenching occurs. The mechanism of concentration quenching is electric dipole - electric dipole interaction. The critical distance for energy transfer between Sm3+ is 1.899 nm. Nano-phosphor YPO4:2% Sm3+ has good thermal stability, and its fluorescence lifetime is 217.99 μs. The activation energy of thermal quenching is 0.2566 eV.

Synthesis of RE6–xCa1.5xSi11N20O (RE = Yb, Lu; x ≈ 2.2) with Lu6–xCa1.5xSi11N20O:Ce3+ Offering Interesting Spectral Properties for Yellow‐Emitting Phosphors in 1pcLEDs

The oxonitridosilicates RE6–xCa1.5xSi11N20O (RE = Yb, Lu; x ≈ 2.2) were synthesized starting from REF3, CaH2, and ”Si(NH)2” in a radiofrequency furnace at 1600 or 1400 °C, respectively. The crystal structure was solved and refined from single‐crystal X‐ray diffraction data of dark red Yb6–xCa1.5xSi11N20O crystals in the trigonal space group P31c (no. 159) with a = 9.8281(10), c = 10.5968(13) Å and Z = 2. The structure represents a filled variant of the Er6Si11N20O structure type, in which the charge difference caused by substitution of trivalent Yb3+ with bivalent Ca2+ is balanced by occupation of an additional third cation site. Synthesis of Lu6–xCa1.5xSi11N20O:Ce3+ resulted in a yellow powder with yellow luminescence. Powder X‐ray data were analyzed by Rietveld refinement based on the crystal data obtained from Yb6–xCa1.5xSi11N20O. The Ce3+ doped compound exhibits a broad emission (fwhm ≈ 168 nm/≈ 5100 cm–1) with a maximum at λem ≈ 565 nm. The emission extends more in the red spectral range compared to YAG:Ce3+, thus making it an interesting phosphor for warm‐white single phosphor converted light‐emitting diodes (1pcLED) with an improved color rendering index.

Tunable white light emission of rare earth ions doped single matrix SrAl2Si2O8 phosphors

Aluminosilicate phosphors have been successfully applied in laser technology and fluorescent lamps due to their high luminescence properties and excellent chemical stability. Consequently, research on novel aluminosilicate phosphors has a good application prospect. Rare earth (RE) ions doped SrAl2Si2O8 phosphors were prepared by solid-phase method. Excited at 350 nm, the phosphor doped with Dy3+ ions emits a blue light peaking at 482 nm and an orange light peaking at 575 nm, respectively, and its optimum doping concentration is 0.8 at.%. At the NUV excitation of 377 nm, the phosphor doped with Tb3+ ions shows emission peaks at 489 nm, 544 nm, 585 nm and 623 nm, and the luminescence intensity is the strongest when the content of Tb3+ is 9 at.%. The concentration quenching mechanism of Dy3+ and Tb3+ RE ions is the electric dipole–dipole interaction. For SrAl2Si2O8:Tb3+, Sm3+ phosphors, the energy transfer efficiency is 85.4%, and the mechanism is electric dipole–quadrupole interaction. For SrAl2Si2O8:Dy3+ and SrAl2Si2O8:Tb3+, Sm3+ phosphors, the best CIE coordinates are (0.275, 0.308), (0.316, 0.386). The consequences display that RE ions doped single matrix SrAl2Si2O8 phosphors can achieve effective white light emission and have high application value in white LEDs.

Luminescence and self-referenced optical temperature sensing performance in Ca2YZr2Al3O12:Bi3+,Eu3+ phosphors

Ca2YZr2Al3O12:Bi3+,Eu3+ phosphors were elaborated by a traditional solid-state reaction method. The luminescence of Ca2YZr2Al3O12:Bi3+ samples, energy transfer from Bi3+ to Eu3+, and the temperature sensing properties of Ca2YZr2Al3O12:Bi3+,Eu3+ samples have been systematically researched. Under the excitation of ultraviolet light, Bi3+ single doped phosphors give 313 and 392 nm emission bands, which origin from the substitutions of Bi3+ instead of Ca2+ and Y3+ sites, respectively. And the color-adjustable emission from blue to red were observed by increasing Eu3+ content in Ca2YZr2Al3O12:Bi3+,Eu3+ samples. Relying on different temperature dependent variation tendency, the fluorescence intensity ratio (FIR) values present outstanding temperature sensing properties. The absolute and relative sensitivity can be up to 0.826 %K-1 and 0.664 %K-1, respectively. All above results suggest that Ca2YZr2Al3O12:Bi3+,Eu3+ phosphor is a potential alternative for optical thermometer.

High Thermal Stability Apatite Phosphors\xa0Ca2La8(SiO4)6O2:Dy3+/Sm3+ for White Light Emission: Synthesis, Structure, Luminescence Properties and Energy Transfer

What ideal w-LED phosphors always aim to do is to achieve a single phase near-sunlight emission phosphor simultaneously with both high luminescence efficiency and high thermal stability at operation temperature. And It is well known that apatite compound phosphors are one of the most promising optical materials to realize those above because of their unique structure enhanced luminescence properties and thermal stability. Here, we synthesized a co-doped single phase apatite phosphors Ca2La8(SiO4)6O2:Dy3+/Sm3+ (CLSO:Dy3+/Sm3+) for white light emission, which was provided with excellent thermal stability and of which luminescence intensity at 150 °C still was 92 percentage of that at room temperature. Moreover, X-ray diffraction technique, Fourier transform infrared spectroscopy, scanning electron microscope were employed to characterization of phase structure and morphology, and consequently pure apatite structure and gravel-like morphology of phosphors were proved. Analysis of photoluminescence spectra indicated that concentration quenching effect exist in single-doped CLSO:Dy3+ phosphors owing to dipole-dipole interaction between Dy3+ ions. It is revealed that maybe exist Dy3+ ↔ Sm3+ bilateral non-radiative energy transfer processes in Dy3+/Sm3+ co-doped CLSO system by PL spectra and decay curves. And variation of Sm3+ ion concentration can control color emission, namely CIE chromaticity coordinates and correlated color temperature, finally to achieve white light emission (0.309,0.309) with CCT 6848 K, able to be a potential candidate for commercial lighting applications.

Phase and photoluminescence evolution of (Mg1−xBax)2SiO4: Eu phosphors

(Mg1−xBax)1.95SiO4:0.05Eu phosphors were synthesized by high temperature solid-state reaction at 1200 °C. The x-ray diffraction analysis showed the host phase changing as x value increasing could be denoted as γ-Mg2SiO4, β-Mg2SiO4 mixture (x < 0.2) → Ba2SiO4, β-Mg2SiO4, γ-Mg2SiO4 mixture (0.2 ≤ x < 0.3) → Ba2SiO4, Ba3MgSi2O8, β-Mg2SiO4 mixture (0.3 ≤ x < 0.7) → Ba2SiO4 (x ≥ 0.7). For Ba2SiO4 phase powder (Mg1−xBax)2SiO4 , x ≥ 0.7), the replacement of Mg into Ba ions could improve the crystallization, and Mg2+ ions prefer 9-coodinated Ba2+(II) ions more than 10-coodinated Ba2+(I) ions. Furthermore, there is no change in the phase when Eu ions adding. Photoluminescence spectra analysis showed that (Mg1−xBax)1.95SiO4:0.05Eu phosphors exhibited from typical Eu3+ line emission to typical Eu2+broad band emission under UV excitation, and the powder would be used as green phosphor when x ≥ 0.3. The intensity of mixture green phosphor (0.3 ≤ x < 0.7) increases as x value increases. While, the intensity of Ba2SiO4 single phase green phosphor (x ≥ 0.7) decreases as x value increases. The high resolution emission spectra of (Mg1−xBax)1.95SiO4:0.05Eu (x ≥ 0.7) analysis indicates 10-coodinated Eu2+(I) contributes more than 9-coodinated Eu2+(II) for the green emission, and bigger Eu2+(I)/Eu2+(II) ratio when more Mg2+ ions incorporating to Ba2SiO4 phase crystal. The high-resolution x-ray photoelectron spectroscopy (XPS) analysis of Eu4d showed the Eu ion valence is rarely affected by cation substitution. So the better crystalline and higher Eu2+(I)/Eu2+(II) ratio could used to explain the luminescence improvement of Ba2SiO4 phase green phosphor with Mg2+ cation substitution.