Search

The solar spectral converters mainly involve the energy transfer between two codoped ions. Here, we report a series of Ce3+, Cr3+, Ln3+ (Ln = Yb, Nd, Er) tridoped Gd3Sc2Ga3O12 (GSGO) phosphors with improved absorption and increasing near infrared (NIR) emission. We observed the multiple energy transfer behaviors of Cr3+→Ln3+, Ce3+→Ln3+, Ce3+→Cr3+, and Ce3+→Cr3+→Ln3+ in GSGO matrix. When Ce3+ is introduced into the GSGO:Cr3+,Ln3+ phosphors, the energy transfer of Ce3+→Cr3+→Ln3+ has been realized by utilizing the energy transfer bridge of the Cr3+ ion. Consequently, GSGO:Ce3+,Cr3+,Ln3+ can absorb almost all ultraviolet and visible (UV–Vis) light and produce strong NIR light thanks to the synergistic effect of Ce3+→Cr3+→Ln3+, improving the photovoltaic conversion efficiency of c-Si solar cells. Our results show that the prepared GSGO:Ce3+,Cr3+,Ln3+ have the potential application in the solar spectral material for c-Si solar cells. Meanwhile, the strategy of multiple energy transfers gives a new way to design the spectral conversion materials with wider absorption for c-Si solar cells.

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.

Traditionally, phosphors are developed by doping activators on standard crystallographic sites of selected inorganic hosts, thus enabling the prediction of their luminescence with some empirical mo...

Novel orange-red-emitting phosphors Ca3M2Ge3O12:Mn2+,Mn4+ (M = Al, Ga) with sufficient red light component were developed, and their lattice occupancy and luminescent properties of different color ...

Gd3Ga5–x–δAlx–y+δO12:yMn solid solutions with improving luminescence properties were prepared via cation substitution and a controllable Mn valence state. The abnormal autoreduction from Mn4+ to Mn...

A series of novel Y3Ga5O12:Bi3+,Mn2+ phosphors with controllable luminescence have been synthesized and their photoluminescence characteristics have been studied in detail with the purpose of developing a single-component white light-emitting phosphor suitable for pc-WLEDs. The Bi3+ singly-doped phosphor shows an intense blue–green emission, while the Mn2+-doped phosphor presents a narrow red emission with a FWHM of 59 nm, which is comparable to the previously reported nitride red phosphor Ca[LiAl3N4]:Eu2+. When Bi3+ and Mn2+ were co-doped into the Y3Ga5O12 matrix, effective energy transfer from the Bi3+ to Mn2+ ions was observed. Subsequently, a single-component warm white light-emitting phosphor was obtained by adjusting the doping ratio of Bi3+ and Mn2+ and by utilizing the energy transfer from the Bi3+ to Mn2+ ions. Moreover, the thermal quenching properties show that the prepared Y3Ga5O12:Bi3+,Mn2+ samples possess good thermal stability of luminescence. Finally, a WLED device with a high Ra of 90, a low CCT of 3908 K, and a CIE color coordinate of (0.3503, 0.3158) has been fabricated using the synthesized phosphor. The results indicate that Y3Ga5O12:Bi3+,Mn2+ phosphors are potential candidates as single-component white light emission phosphors applied in WLEDs. Moreover, this strategy is also conducive for the design of novel white light emission phosphors for pc-WLEDs.

Novel La8Ba2(Si4P2O22N2)O2:Eu2+/Ce3+/Tb3+ apatite phosphors with tuneable light emission have been successfully synthesized by the conventional solid-state method. The structural and luminescence properties of the newly obtained samples have been studied systematically. The photoluminescence properties show that the Eu2+-, Ce3+- and Tb3+-doped La8Ba2(Si4P2O22N2)O2 samples have strong absorption in the near ultraviolet (n-UV) region. Under n-UV light irradiation, Eu2+-doped samples exhibit a narrow bluish green emission band peaking at 496 nm with a full width at half-maximum (FWHM) of 55 nm, which is comparable to the commercial blue emitting BaMgAl10O17:Eu2+ (FWHM = 55 nm) phosphor, while La8Ba2(Si4P2O22N2)O2:Ce3+,Tb3+ presents adjustable emission colour from violet to green by adjusting the concentration of Tb3+. The energy-transfer efficiencies and mechanisms have been discussed in detail. The temperature dependent luminescence measurements show that the obtained samples have low thermal quenching. Moreover, a series of white LED devices have been obtained by using the La8Ba1.99(Si4P2O22N2)O2:0.01Eu2+/(Sr,Ca)AlSiN3:Eu2+/(Ba,Sr)SiO4:Eu2+/(Sr,Ba,Ca)10(PO4)Cl2:Eu2+/Sr2SiO4:Eu2+ phosphor blend. By adding the as-prepared narrow bluish-green-emitting La8Ba1.99(Si4P2O22N2)O2:0.01Eu2+ phosphor, the Ra values can increase from 68 to 98, the R9 values increase from 42 to 95, and the corresponding CCT continuously decreases from 6210 to 3086 K, respectively. Our results reveal that the Eu2+, Ce3+ and Tb3+ activated phosphors are promising candidates for WLEDs.

The recently discovered Sr[Li$_2$Al$_2$O$_2$N$_2$]:Eu$^{2+}$ red phosphor, candidate for the next generation of eco-efficient white light-emitting diodes, exhibits excellent emission spectral position and exceptionally small linewidth. It belongs to the UCr$_4$C$_4$-structure family of phosphors, containing many potential candidates commercial phosphors, whose small linewidth, tentatively ascribed to the high-symmetry cuboid environment of the doping site, has drawn the attention of researchers in the last five years. We use density functional theory, $\Delta$SCF method and configuration coordinate models (CCM) to provide a complete characterization of this material. Using a multi-dimensional CCM, an accurate description of the coupling of the vibronic structure with the electronic 5d$\rightarrow$4f transition is obtained, including the partial Huang-Rhys factors and frequency of the dominant modes. We show that, in addition to the first-coordination shell cuboid deformation mode, low-frequency phonon modes involving chains of strontium atoms along the tetragonal axis shape the emission linewidth in Sr[Li$_2$Al$_2$O$_2$N$_2$]:Eu$^{2+}$. This finding sheds new light on the emission properties of UCr$_4$C$_4$-structure phosphors, possessing similar Ca/Sr/Ba channel. Our approach provides a robust theoretical framework to systematically study the emission spectra of such Eu-doped phosphors, and predict candidates with expected similar or even sharper linewidth.

Understanding the physical mechanisms behind thermal effects in phosphors is crucial for white light-emitting device (WLEDs) applications, as thermal quenching of their photoluminescence might render them useless. We analyze from first-principles, before and after absorption/emission of light, two chemically close Eu-doped Ba3Si6O12N2 and Ba3Si6O9N4 crystals for WLEDs. The first one has an almost constant emission intensity with increasing temperature whereas the other one does not. Our results, in which the Eu-5d levels are obtained inside the band gap thanks to the removal of an electron from the 4f7 shell, and the atomic neighborhood properly relaxed in the excited state, attributes the above-mentioned experimental difference to an autoionization model of the thermal quenching, based on the energy difference between Eu5d and the conduction band minimum. Our depleted-shifted 4f method can identify luminescent centers and therefore allows for effective crystal site engineering of luminescent centers in p...

We study from first principles the emission linewidth of Eu 2 + -doped LED phosphors. Based on the one-dimensional configuration coordinate model, an analysis of first principles data obtained for fifteen compounds show that, at working temperature, the linewidth of Eu 2 + emission band in solids is negligibly affected by quantum effects, and can be extracted from the Franck–Condon energy shifts. For a fixed Stokes shift, the difference of Franck–Condon energy shifts in the excited and ground states is the key factor for the FWHM determination. Narrow emission Eu 2 + -doped LED phosphors are expected for the case with large positive value of such difference.

An emitting tunable Mg 2 Al 4 Si 5 O 18 :Ce 3+ /Mn 2+ /Tb 3+ phosphors have been synthesized by high-temperature solid-state reaction technique. In this system, Mg 2 Al 4 Si 5 O 18 :Ce 3+ , Mn 2+ samples exhibit two dominating bands situated at 430 and 640 nm, originating from the Ce 3+ , Mn 2+ ions, respectively. Photoluminescence and energy transfer in Mg 2 Al 4 Si 5 O 18 :Ce 3+ , Mn 2+ are investigated as a function of Mn 2+ concentrations. The intensity ratios of red to blue band as a function of Mn 2+ concentrations are calculated based on the analysis of the luminescence dynamical process as well as fluorescence lifetime measurements, and the results are in good agreement with that obtained directly from emission spectra. Additionally, by incorporation of Tb 3+ , an efficient energy transfer from Ce 3+ to Tb 3+ was found and the energy transfer efficiency reaches 52% at y = 0.05. Results indicated that the emitting colors can be adjusted from blue to red via the energy transfer of Ce 3+ → Mn 2+ and from blue to green via the energy transfer of Ce 3+ → Tb 3+ .

The luminescence of fifteen representative Eu$^{2+}$-doped phosphors used for white-LED and scintillation applications is studied through a Constrained Density Functional Theory. Transition energies and Stokes shift are deduced from differences of total energies between the ground and excited states of the systems, in the absorption and emission geometries. The general applicability of such methodology is first assessed: for this representative set, the calculated absolute error with respect to experiment on absorption and emission energies is within 0.3 eV. This set of compounds covers a wide range of transition energies that extents from 1.7 to 3.5 eV. The information gained from the relaxed geometries and total energies is further used to evaluate the thermal barrier for the $4f-5d$ crossover, the full width at half-maximum of the emission spectrum and the temperature shift of the emission peak, using a one-dimensional configuration-coordinate model. The former results indicate that the $4f-5d$ crossover cannot be the dominant mechanism for the thermal quenching behavior of Eu$^{2+}$-doped phosphors and the latter results are compared to available experimental data and yield a 30$\%$ mean absolute relative error. Finally, a semi-empirical model used previously for Ce$^{3+}$-doped hosts is adapted to Eu$^{2+}$-doped hosts and gives the absorption and emission energies within 0.9 eV of experiment, underperforming compared to the first-principles calculation., 17 pages, 13 figures, (Phys. Rev. B 2017 Accept)

In search of a reliable methodology for the prediction of light absorption and emission of Ce$^{3+}$-doped luminescent materials, 13 representative materials are studied with first-principles and semiempirical approaches. In the first-principles approach, that combines constrained density-functional theory and $\Delta$SCF, the atomic positions are obtained for both ground and excited states of the Ce$^{3+}$ ion. The structural information is fed into Dorenbos' semiempirical model. Absorption and emission energies are calculated with both methods and compared with experiment. The first-principles approach matches experiment within 0.3 eV, with two exceptions at 0.5 eV. In contrast, the semiempirical approach does not perform as well (usually more than 0.5 eV error). The general applicability of the present first-principles scheme, with an encouraging predictive power, opens a novel avenue for crystal site engineering and high-throughput search for new phosphors and scintillators., Comment: 12 pages, 3 figures

We reported a single-phased CaScAlSiO 6 :Ce 3+ , Tb 3+ , Eu 3+ as a potential full-color emitting phosphor for the application in fluorescent lamps. The CaScAlSiO 6 :Ce 3+ , Tb 3+ , Eu 3+ phosphor exhibits three bands under 254 nm excitation: one band situated at 380 nm is attributed to the 5d → 4f transitions of Ce 3+ ions, the second band with sharp lines peaked at 542 nm is assigned to the 5 D 4 → 7 F J transitions of Tb 3+ ions, the third band in the orange–red region (580–700 nm) is originated from 5 D 0 → 7 F J transitions of Eu 3+ ions. The Commission Internationale de I’Eclairage (CIE) chromaticity coordinates (0.30, 0.30) and high color rendering index (CRI=88) can be achieved upon excitation of 254 nm light. It is suggested that CaScAlSiO 6 :Ce 3+ , Tb 3+ , Eu 3+ can serve as a potential single-phased full-color emitting phosphor for phosphor-converted fluorescent lamps.

In this paper, a novel divalent europium-doped green emitting blue convertible K2Ba7Si16O40:Eu2+ phosphor has been synthesized successfully via high-temperature solid-state reaction. The structure of K2Ba7Si16O40:Eu2+ has been refined on the basis of X-ray powder diffraction by Rietveld refinement method, which consists of two infinite dimensional layers of corner-sharing [SiO4] tetrahedral parallel to (201) linked together through eight-coordinate K and seven- and nine-coordinate Ba atoms. Under excitation of blue light, the K2Ba7Si16O40:Eu2+ phosphor emits a strong green emission band peaking at 500 nm. The concentration quenching mechanism of the Eu2+ ion was discussed and the critical distance was calculated. Furthermore, the phosphor exhibits high quantum efficiency and good thermal stability, indicating that the K2Ba7Si16O40:Eu2+ phosphor can serve as an effective green emitting candidate for blue light down-conversion white light emitting diodes.

In this paper, Ce3+ doped and Ce3+,Mn2+ co-doped Na2Ba6(Si2O7)(SiO4)2 phosphors were synthesized via a high temperature solid-state reaction. The Rietveld refinement analysis of the X-ray diffraction patterns confirmed the formation of the single phase of Na2Ba6(Si2O7)(SiO4)2. The PL spectrum of the Ce3+ single-doped phosphor shows a broad asymmetric band extending from 350 to 600 nm peaking at 420 nm under the excitation of UV light. Also, the low temperature (5 K) PL spectrum shows clearly three peaks at 375, 420, and 451 nm, which is in accordance with the Ce3+ ion site in the host. The Ce3+,Mn2+ co-doped phosphors show a blue emission band and an orange emission band, and the corresponding CIE coordinates intuitively indicate the tunable colors from the blue to green area. And the energy transfer mechanism from Ce3+ to Mn2+ in the host has been verified to be a dipole–quadrupole interaction. In addition, the emission intensity of Na2Ba6(Si2O7)(SiO4)2:0.01Ce3+ phosphor slightly changed with the temperature increase from 300 to 450 K, revealing that the obtained phosphor possesses an excellent thermal stability, which makes it an attractive candidate phosphor for white lighting emitting diodes.

A series of Eu2+ and Ce3+/Tb3+ doped Ca2NaSiO4F (CNSOF) phosphors have been synthesized and their structure and photoluminescence properties have been investigated in detail. Rietveld structure refinement indicates that the phosphors crystalized in an orthorhombic system with a space group of Pnma (no. 62) and there are two kinds of cation sites for the doped ions to occupy in forming emission centers. The CNSOF:Eu2+ and CNSOF:Ce3+ phosphors both have broad excitation bands, which match well with the commercial UV LED chips. The CNSOF:Eu2+ phosphor can have intense green emission with a maximum at 530 nm under irradiation at 380 nm, while the CNSOF:Ce3+ sample can emit intense blue light, peaking at 470 nm with excitation at 365 nm. By codoping the Tb3+ and Ce3+ ions into an CNSOF host and varying their relative ratio, tunable blue-green colors are obtained due to efficient energy transfer from the Ce3+ to Tb3+ ions. Moreover, energy transfer mechanisms for the Eu2+ ions in CNSOF:Eu2+ and Ce3+ → Tb3+ in CNSOF:Ce3+,Tb3+ have been studied systematically. Our investigation indicates that CNSOF:Eu2+ and CNSOF:Ce3+,Tb3+ may be potential green and blue-green phosphors for UV WLEDs, respectively.

A series of Eu2+ and Mn2+ activated novel Sr3GdNa(PO4)3F phosphors have been prepared through a high temperature solid state reaction. The investigation revealed that Sr3GdNa(PO4)3F crystallized in a hexagonal crystal system with the space group P (no. 147). The Eu2+ activated phosphors can be efficiently excited in the range of 250 to 420 nm, which matches well with the commercial n-UV LED chips, and give intense blue emission centering at 470 nm. By codoping the Eu2+ and Mn2+ ions into the SGNPF host and singly varying the doping content of the Mn2+ ion, tunable colors from blue to white and then to yellow are obtained in SGNPF:Eu2+,Mn2+ phosphors under the irradiation of 390 nm. The energy transfer from the Eu2+ to Mn2+ ions is demonstrated to be a dipole–quadrupole mechanism in terms of the experimental results and analysis of photoluminescence spectra and decay curves of the phosphors. The critical distance between the Eu2+ and Mn2+ ions in SGNPF:Eu2+,Mn2+ was determined by the spectral overlap method. The investigation indicates that our prepared samples might have potential application in WLEDs.

A series of Ca2SrAl2O6:Ce(3+),Li(+),Mn(2+) phosphors have been synthesized by traditional solid state reactions. The structure and photoluminescence properties of the samples together with the energy transfer from Ce(3+) to Mn(2+) ions have been investigated in detail. The obtained phosphors can be excited efficiently by UV excitation and exhibit a broad blue-green emission band peaking at 470 nm and an orange-red emission band at 610 nm, which result from the f-d transition of the Ce(3+) and the (4)T1-(6)A1 transition of the Mn(2+) ions, respectively. By varying the doping concentration of the Mn(2+) ion, a series of tunable colors including white are obtained at an irradiation of 355 nm. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis of photoluminescence spectra and decay curves of the phosphors. The critical distance between the Ce(3+) and Mn(2+) ions has been calculated by both the concentration quenching method and the spectral overlap method. Preliminary studies on the properties of the phosphor indicated that our prepared Ca2SrAl2O6:Ce(3+),Li(+),Mn(2+) phosphor might have potential application as a single-phase white-emitting phosphor for WLEDs.

In this paper, a novel green phosphor ca8mg3al2si7o28:eu2+ is synthesized via a conventional high-temperature solid-state reaction. the crystal structure of the phosphor is confirmed from the rietveld method. the obtained phosphor has a wide absorption band from the uv to the visible spectral region, ranging from 230 to 450 nm, which fits well with the characteristic emission of uv light-emitting diode (led) chips. upon excitation at 420 nm, the phosphor shows a bright and broad green color emission band with a maximum centered at 535 nm, which is attributed to the parity and spin allowed 5d-4f transition. the longer emission wavelength is caused by both the d orbital preferential orientation and the lowered symmetry of the eu2+ ions caused by the discrepancy of the tetrahedrons composed of mgo4, sio4, and alo4. additionally, the energy transfer mechanism among eu2+ ions is demonstrated via a dipole-dipole interaction by the luminescence spectra and the fluorescence decay analysis calculations on the basis of the inokuti-hirayama model. furthermore, the thermal stability of the phosphor is investigated in detail. these results suggest that the ca8mg3al2si7o28:eu2+ phosphor has great potential to be a green phosphor for white light emitting diodes (wleds).

We have synthesized a series of (Ce3+,Tb3+,Eu3+) singly doped & (Ce3+/Tb3+, Ce3+/Mn2+) codoped NaY9(SiO4)(6)O-2 phosphors via high temperature solid state reaction and investigated their crystal structures and luminescent properties in detail. The singly doped phosphors exhibit the characteristic emission of activators under UV excitation, respectively. And the decay curves can be fitted well by the two exponential functions, which is consistent with the presence of two various Y3+ sites in the host. On the basis of the photoluminescence emission spectra of codoped NaY9(SiO4)(6)O-2 samples, we clearly observed the sensitizing effects from the Ce3+ ions to the Tb3+ or Mn2+ ions and coarsely calculated the energy transfer efficiency. Furthermore, the color tune of these codoped NaY9(SiO4)(6)O-2 phosphors can be easily obtained by adjusting the relative content between the Ce3+ and Tb3+/Mn2+. (C) 2013 The Electrochemical Society. All rights reserved.

Single-phased Ca3Si2O7:Ce3+,Eu2+ phosphor has been successfully prepared by the high temperature solid-state method. The phosphor shows efficient excitation bands from 200 to 400 nm and adjustable emission bands through the energy transfer from the Ce3+ to Eu2+ ions. The color hues can change from blue towards white ultimately to orange by adjusting the percentage content of doping ions. The investigation reveals that an electric dipole-dipole reaction mechanism should be responsible for the energy transfer from the Ce3+ to Eu2+ ions. The critical distance was obtained from the spectral overlap in terms of Dexter's theory. The developed phosphor Ca3Si2O7:Ce3+,Eu2+ exhibits two bands at 440 and 625 nm, respectively, which reveling that it has a great potentiality to be an UV-convertible phosphor for white-light emitting diodes with low color temperature. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

Monodispersed CaWO4 and CaWO4:Mo/Eu, Tb microspheres have been obtained hydrothermally with excellent reproducibility. X-ray diffraction, field-emission scanning electron microscopy and photoluminescence were used to characterize the as-synthesized samples. The results uncover the formation process of the microspheres and the influence of ethylenediamine. Doping proper concentration of Mo into CaWO4 micropheres can extend the excitation range as the incorporation induces obvious redshift. We have also tuned the color from blue to pink blue, white and green only by varying the relative content of Eu-Tb in the CaWO4 host. (C) 2011 Elsevier B.V. All rights reserved.

A novel tunable full-color-emitting Sr3Gd(PO4)3:Eu2+,Mn2+ phosphor system was successfully developed. Its excitation wavelength ranging from 230 to 450 nm fits well with the characteristic emission of UV light-emitting diode (LED) chips. The color emission of these phosphors can be tuned across almost the entire visible light spectrum resulting in white light emission with varied hue and correlated color temperature (CCT) by varying the molar ratios of Eu2+ and Mn2+. Moreover, the efficient energy transfer from Eu2+ to Mn2+ was demonstrated via a dipole–quadrupole mechanism by the luminescence spectra and the fluorescence decay dynamics based on the Inokuti–Hirayama theoretical model. These results indicate that the developed phosphor may be promising as a single-component white-light-emitting phosphor for white LEDs.

A series of single-component Sr3Lu(PO4)3:Eu2+,Mn2+ phosphors were successfully synthesized by solid-state reaction, and their photoluminescence properties were investigated. The Sr3Lu(PO4)3:Eu2+,Mn2+ phosphor system was efficiently excited at wavelength ranging from 250 to 420 nm, which is well-matched with ultraviolet (UV) light-emitting diode (LED) chips. As a result of fine-tuning of the emission composition of the Eu2+ and Mn2+ ions, warm white light emission can be realized by combining the emission of Eu2+ and Mn2+ in a single host lattice under UV light excitation. Efficient resonant energy transfer from the Eu2+ to Mn2+ ions was demonstrated to be a dipole–quadrupole mechanism in such system, and the energy transfer efficiency increases with an increase in the Mn2+ doping content, which was confirmed by the luminescence spectra and fluorescence decay curves. In addition, the energy transfer efficiency and critical distance were also calculated. The results indicate that the developed phosphor can ...

The blue-emitting phosphors Ca (4− x ) Eu x Si 2 O 7 F 2 (0 x ⩽ 0.05) have been prepared by solid-state reaction and the photoluminescence properties have been studied systematically. The electronic structure of calcium fluoride silicate Ca 4 Si 2 O 7 F 2 was calculated using the CASTEP code. The calculation results of electronic structure show that Ca 4 Si 2 O 7 F 2 has an indirect band gap with 5 eV. The top of the valence band is dominated by O 2p and Si 3p states, while the bottom of the conduction band is mainly composed of Ca 3d states. Under the 350 nm excitation, the obtained sample shows a broad emission band in the wavelength range of 400–500 nm with peaks of 413 nm and 460 nm from two different luminescence centers, respectively. The relative intensity of the two peaks changes with the alteration of the Eu 2+ concentration. The strong excitation bands of the powder in the wavelength range of 200–420 nm are favorable properties for the application as lighting-emitting-diode conversion phosphor.

The title phosphor is synthesized by solid state reaction of NaNO3, BaCO3, SiO2, CeO2, and MnCO3 (5% H2—95% N2, 1050 °C, 8 h) and characterized by XRD and photoluminescence spectroscopy.

Presently considerable interest in phosphor-converted warm LEDs which meet the stringent requirements of general illumination is stimulated. Here we report warm white LEDs made by altering the crystal structure and doping ions, which can govern the luminescence pattern to modulate the correlated color temperature and color-rendering index.

A series of (Ba1-mEum) 3La1-nTbnNa(PO4)3F (m = 0—0.07; n = 0—0.60) phosphors are prepared by solid state reaction of BaCO3, BaF2, La2O3, Na2CO3, NH4H2PO4, Eu2O3, and Tb4O7 (20% H2/80% N2, 1050 °C, 3 h).

Hexagonal GdF3 is a more efficient phosphor host compared with the traditional orthorhombic form but the hexagonal phase is thermodynamically unstable at room temperature. Herein, we present a strategy to stabilize hexagonal GdF3 by doping with alkaline-earth ions in a mild hydrothermal reaction system. The selection of the dopant, effect of the dopant amount and the mechanism of the phase transition was discussed in detail. The luminescence variation of GdF3:Eu was demonstrated to verify the phase transformation. Furthermore, the upconversion luminescence of the Sr-doped and undoped GdF3:Yb/Er was investigated.

Near-UV convertible Eu(3+)-activated orange oxynitride phosphors have been obtained via a Ce(3+)→ Tb(3+)→ Eu(3+) energy transfer mechanism. The Tb(3+) ions play the role of an energy transfer bridge to connect the Ce(3+) and Eu(3+) ion pairs, and an optimal concentration of the Tb(3+) ion is necessary for maximum intensity of the Eu(3+) ion emission.

A series of single-component red/white-emitting Ce3+,Tb3+,Mn2+-doped CaScAlSiO6 phosphors are synthesized by solid state reaction of CaCO3, Sc2O3, SiO2, Al2O3, CeO2, Tb4O7, and MnCO3 (10% H2/N2, 1400 °C, 4 h).

A series of single-component red/white-emitting CaScAlSiO6:Ce(3+),Tb(3+),Mn(2+) phosphors have been synthesized by a solid-state reaction. It is observed that CaScAlSiO6:Ce(3+),Tb(3+) phosphors exhibit two dominating bands situated at 380 and 542 nm, originating from the allowed 5d → 4f transition of the Ce(3+) ion and the (5)D4 → (7)F(J) = (J = 6, 5, 4, 3) transition of the Tb(3+) ion, respectively. As for CaScAlSiO6:Ce(3+),Mn(2+), our results indicate that Mn(2+) may occupy not only a Ca(2+) site to generate an orange emission [Mn(2+)(I)] at 590 nm but also a Sc(3+) site to generate a red emission [Mn(2+)(II)] at 670 nm. Both energy transfers from Ce(3+) to Tb(3+) and from Ce(3+) to Mn(2+) in the CaScAlSiO6 host are investigated and have been demonstrated to be of the resonant type via a dipole-dipole mechanism. By proper tuning of the relative composition of Tb(3+)/Mn(2+), white light can also be achieved upon excitation of UV light, indicating that the developed phosphor may potentially be used as a single-component red/white-emitting phosphor for UV-light-emitting diodes.

The Eu(2+) → Tb(3+) → Sm(3+) energy transfer scheme has been proposed to realize the sensitization of Sm(3+) ion emission by Eu(2+) ions. Following this energy transfer model, near-UV convertible Sm(3+)-activated orange phosphors have been obtained in Sr3Y(PO4)3:Eu(2+), Tb(3+), Sm(3+) powders.

Eu(2+)-Mn(2+) codoped orange-yellow-emitting Ba(3)Lu(PO(4))(3) phosphors were synthesized by a solid-state reaction. The synthesis, structure refinement, and luminescence properties of the obtained phosphor were first investigated in detail. The crystal structure was refined with a split-atom model, where the oxygen atoms are distributed over two partially occupied sites. The refinement confirmed that BLuP:0.005Eu(2+),0.06Mn(2+) has a cubic unit cell with space group I43d (no. 220), cell parameters a = b = c = 10.4025 Å and Z = 4. The luminescent properties reveal that the developed phosphor can efficiently convert UV photons in a broad range from 230 to 430 nm into orange-yellow emission. On the basis of the luminescence spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu(2+) to Mn(2+) ions takes place in the codoped Ba(3)Lu(PO(4))(3):Eu(2+),Mn(2+) phosphor, and the energy transfer efficiency increases with an increase in the Mn(2+) content. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis. In particular, our developed phosphor contains a larger amount of the red-emitting component, compared with the commercial YAG:Ce phosphor, possessing favorable properties for application in warm white LEDs with low correlated color temperature.

A novel orange-yellow-emitting Ba(3)Gd(PO(4))(3):xEu(2+),yMn(2+) phosphor is prepared by high-temperature solid-state reaction. The crystal structure of Ba(3)Gd(PO(4))(3):0.005 Eu(2+),0.04 Mn(2+) is determined by Rietveld refinement analysis on powder X-ray diffraction data, which shows that the cations are disordered on a single crystallographic site and the oxygen atoms are distributed over two partially occupied sites. The photoluminescence excitation spectra show that the developed phosphor has an efficient broad absorption band ranging from 230 to 420 nm, perfectly matching the characteristic emission of UV-light emitting diode (LED) chips. The emission spectra show that the obtained phosphors possess tunable color emissions from yellowish-green through yellow and ultimately to reddish-orange by simply adjusting the Mn(2+) content (y) in Ba(3)Gd(PO(4))(3):0.005 Eu(2+),y Mn(2+) host. The tunable color emissions origin from the change in intensity between the 4f-5d transitions in the Eu(2+) ions and the (4)T(1)-(6)A(1) transitions of the Mn(2+) ions through the energy transfer from the Eu(2+) to the Mn(2+) ions. In addition, the mechanism of the energy transfer between the Eu(2+) and Mn(2+) ions are also studied in terms of the Inokuti-Hirayama theoretical model. The present results indicate that this novel orange-yellow-emitting phosphor can be used as a potential candidate for the application in white LEDs.

The new title phosphor is synthesized by solid state reaction of MgO, Lu2O3, Al2O3, SiO2, CeO2, and MnCO3 (CO atmosphere, 1350 °C, 3 h) and characterized by XRD and photoluminescence spectroscopy.

A series of the solid-solution phosphors Lu(3-x-y)Mn(x)Al(5-x)Si(x)O(12):yCe(3+) is synthesized by solid-state reaction. The obtained phosphors possess the garnet structure and exhibit similar excitation properties as the phosphor Lu(3)Al(5)O(12):Ce(3+), but with an effectively improved red component in the emission spectrum. This can be attributed to the energy transfer from Ce(3+) to Mn(2+). Our investigation reveals that electric dipole-quadrupole interactions dominate the energy-transfer mechanism and that the critical distance determined by the spectral overlap method is about 9.21 A. The color-tunable emissions of the Lu(3-x-y)Mn(x)Al(5-x)Si(x)O(12):yCe(3+) phosphor as a function of Mn(3)Al(2)Si(3)O(12) content are realized by continuously shifting the chromaticity coordinates from (0.354, 0.570) to (0.462, 0.494). They indicate that the obtained material may have potential application as a blue radiation-converting phosphor for white LEDs with high-quality white light.

Ce(3+) and Eu(2+) singly doped and Ce(3+)/Eu(2+)-codoped Ca(7)Mg(SiO(4))(4) phosphors are synthesized by the conventional solid state reaction. The Ce(3+) activated sample exhibits intense blue emission under 350 nm excitation, the composition-optimized Ca(7)Mg(SiO(4))(4) : 4%Ce(3+) shows better color purity than the commercial blue phosphor, BaMgAl(10)O(17) : Eu(2+) (BAM : Eu(2+)) and exhibits superior external quantum efficiency (65%). The Ca(7)Mg(SiO(4))(4) : Eu(2+) powder shows a broad emission band in the wavelength range of 400-600 nm with a maximum at about 500 nm. The strong excitation bands of the Ca(7)Mg(SiO(4))(4) : Eu(2+) in the wavelength range of 250-450 nm are favorable properties for applications as light-emitting-diode conversion phosphors. Furthermore, the energy transfer from the Ce(3+) to Eu(2+) ions is observed in the codoped samples, the resonance-type energy transfer is determined to be due to the dipole-dipole interaction mechanism and the critical distance is obtained through the spectral overlap approach and concentration quenching method.

In this paper, a novel single-phased white light emitting phosphor Na2Ca4Mg2Si4O15:Eu2+, Mn2+ was prepared successfully via the high temperature solid state reaction. The obtained Na2Ca4Mg2Si4O15:Eu2+ phosphor exhibits a broad excitation band ranging from 200 to 450 nm and a blue light emission band peaking at 480 nm, originating from 4f7 ↔ 4f65 d1 (f-d) electric dipole allowed transitions of Eu2+ ions. Due to the energy transfer from Eu2+ to Mn2+ ions, the co-doped Eu2+ ions in the Na2Ca4Mg2Si4O15:Eu2+, Mn2+ phosphors markedly enhances the luminescence intensity of Mn2+ ions, providing highly attractive tunable color. The luminescent mechanism invoking the energy transfer between Eu2+ ions and Mn2+ ions has been certified to be dipole–quadrupole interaction predominantly through the investigations of the luminescence spectra and the fluorescence decay curves. Our results show that the novel Na2Ca4Mg2Si4O15:Eu2+, Mn2+ phosphor is a very promising candidate for UV white light emitting diodes.

Emission-tunable Mg2Al4Si5O18:Eu2+, Mn2+ and Mg2Al4Si5O18:Eu2+, Tb3+ cordierite phosphors have been synthesized by a high-temperature solid-state reaction technique. Photoluminescence and energy transfer in Mg2Al4Si5O18:Eu2+, Mn2+ occur via a resonance-type dipole–quadrupole interaction mechanism, and the critical distance of the energy transfer is calculated to be 11.1 A. We found that the emission colors could be tuned from blue (0.19, 0.26) to white (0.41, 0.37) via the energy transfer of Eu2+ → Mn2+ and from blue to green (0.28, 0.45) via the energy transfer of Eu2+ → Tb3+. The green emission is realized in the Mg2Al4Si5O18:Eu2+, Tb3+ phosphors on the basis of the highly efficient energy transfer from the Eu2+ to Tb3+ ions. Finally, the color tunable emission with varied hues has been obtained in Eu2+, Tb3+, or Mn2+ activated Mg2Al4Si5O18 phosphors, making them potential emission-tunable phosphors for near-UV LEDs.

Incorporating Tb3+ and Mn2+ into a high efficiency BaCa2MgSi2O8:Eu2+ phosphor generates a green line peaking at 542 nm and a red emission band peaking at 660 nm. Upon 365 nm excitation, the absolute quantum yields of BaCa2MgSi2O8:Eu2+ phosphors doped with various Tb3+ ions all exceed 77%, indicating that the phosphor is a suitable matrix for rare earth ion doping. Meanwhile, the luminescent properties of BaCa2MgSi2O8:Eu2+,Mn2+ were investigated and remarkable energy transfer from the blue emitting Eu2+ to both Tb3+ and Mn2+ can occur in the BaCa2MgSi2O8 system. This energy transfer is important in enabling the achievement of a broad emission spectrum, covering a red spectral region, suitable for a near-UV light-emitting diode (LED) excitation. The decay patterns of the red and blue fluorescence are discussed in relation to the effect of the energy transfer. Measurement of the thermal quenching properties reveals that BaCa2MgSi2O8:Eu2+,Mn2+ exhibits excellent characteristics.

An orange-emitting phosphor was obtained via efficient Ce3+–Mn2+ and Eu2+–Mn2+ energy transfers in La9.33(SiO4)6O2, and has been developed for solid state UV/near-UV white lighting applications. The luminescence properties and energy transfer from Ce3+ to Mn2+ and Eu2+ to Mn2+ are investigated. The La9.33(SiO4)6O2:Ce3+, Mn2+ phosphor shows a blue emission centered at 380 and an orange emission peaking at 590 nm, which could be ascribed to the allowed 5d → 4f transition of the Ce3+ ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ion, respectively. Upon excitation at 365 nm, the Eu2+, Mn2+ co-doped La9.33(SiO4)6O2 phosphor exhibits the Eu2+ green emission band and the Mn2+ orange emission band. Non-radiative transitions between the Ce3+/Eu2+ and Mn2+ ions in the La9.33(SiO4)6O2 host are both demonstrated to be attributable to dipole–quadrupole interactions. The intensity ratio of the Mn2+ emission bands can be enhanced through the increase of the Mn2+ content, which is attributed to the efficient energy transfer from Ce3+/Eu2+ to Mn2+, and the corresponding chromaticity coordinates (0.50, 0.38), (0.51, 0.46) were obtained with the La9.33(SiO4)6O2:Ce3+, Mn2+ and La9.33(SiO4)6O2:Eu2+, Mn2+ samples. Results indicated that the as-prepared phosphors might have promising applications in white-light LEDs as an orange-emitting phosphor.

A n-UV convertible phosphor Sr3Tb(PO4)3:Mn(2+) with tunable-emitting color has been synthesized by solid state reaction. The GSAS refinement shows that the obtained powder crystallizes as a cubic unit cell with space group I43d, and Mn(2+) ions occupy the Sr(2+) crystallographic sites. Under (7)F6→(5)D3 of Tb(3+) excitation at 381 nm, Sr3Tb(PO4)3:Mn(2+) not only exhibits (5)D4→(7)F6-3 of Tb(3+) green emission lines but also (4)T1→(6)A1 of the Mn(2+) orange emission band. In addition, the intensity ratio of the orange/green emission bands can be enhanced through the increase of Mn(2+) content. The intense orange emission band of the Mn(2+) ions is attributed to the efficient energy transfer from the Tb(3+) to Mn(2+) ions, which has been justified through the luminescence spectra and fluorescence decay dynamics. The energy transfer mechanism was demonstrated to be the electric dipole-dipole interaction based on the Inokuti-Hirayama theoretical model, and the energy transfer efficiency was calculated. Optimal-composition samples show high external quantum efficiency, up to 59.3%, indicating the potential of the powder as a n-UV convertible phosphor for white LEDs.

A broadband direct warm-white-emitting phosphor Sr3Sc(PO4)3:Eu(2+), Mn(2+) (SSP:Eu(2+), Mn(2+)) was prepared by a solid-state reaction. The powder X-ray diffraction data, photoluminescence spectra, fluorescence decay curves, quantum efficiency, and chromaticity coordinates of the obtained phosphors were measured and discussed in detail. The results reveal that there is efficient energy transfer from the Eu(2+) to the Mn(2+) ions and the broadband direct warm-white-light comes from the emissions of the Eu(2+) and Mn(2+) ions. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis. We demonstrate the ability to tune the color tone, the correlated color temperature (CCT), and the chromaticity coordinates which can approach the color properties required for solid state lighting. The developed phosphors can be efficiently excited in the UV region and exhibit a warm-white-light emission, making them attractive as single-component white-light-emitting conversion phosphors for UV-based white light emitting diodes.

A series of NaCa2LuSi2O7F2:xCe(3+),yMn(2+) phosphors are firstly prepared by a high-temperature solid-state reaction technique. The Rietveld refinement analysis confirmed that the obtained phosphors have a pure crystalline phase with cuspidine-group structure. NaCa2LuSi2O7F2:xCe(3+),yMn(2+) phosphors can be efficiently excited by UV light and have two emission bands at about 410 and 600 nm. The luminescent properties of the singly-doped samples reveal that the Ce(3+) ions occupy two different Lu(3+) sites in the host lattice. We observed an efficient energy transfer from the Ce(3+) to Mn(2+) ions. The investigation revealed that the mechanism of the energy transfer was a resonant type via a nonradiative dipole-quadrupole interaction. The hues can be adjusted and white light can be obtained by tuning the concentration of Mn(2+) ions in the codoped phosphors through the energy transfer from the Ce(3+) to Mn(2+) ions, hinting a promising application of NaCa2LuSi2O7F2:xCe(3+),yMn(2+) as a single-component phosphor that can produce white light from UV-based LEDs.

A series of Eu(3+), Tb(3+), Tm(3+) singly and triply doped Ca3Bi(PO4)3 (CBP) phosphors were synthesized by solid-state reaction. Their structure and photoluminescence (PL) properties were first investigated in detail. Rietveld refinement analysis confirmed that the CBP has a cubic unit cell. Its space group was determined to be I4[combining macron]3d with cell parameters a = b = c = 9.941 Å and Z = 4. In addition, the Ca3Bi(PO4)3 shows both cation disorder and oxygen sublattice disorder. For the CBP:Eu(3+) phosphor, the charge transfer bands in the PLE spectra were different at 293 K and 4.3 K, and a model was presented to give a possible explanation for this phenomenon. CBP:Eu(3+) shows intense red emission due to (5)D0-(7)F2 transition and its integral emission intensity and quantum efficiency are higher than the commercial Y2O3:Eu(3+) phosphor under irradiation of 397 nm, indicating that the CBP:Eu(3+) phosphor might have potential application in the NUV range for solid-state lighting. The CBP:Tb(3+) and CBP:Tm(3+) phosphors show intense green and blue emission due to (5)D4-(7)F2 transition of the Tb(3+) ions and the (1)D2-(3)F4 transition of the Tm(3+) ions, respectively. The energy transfer from the Tb(3+) to Eu(3+) ions was also validated by the spectra and decay curves of the Tb(3+) ions. Tunable emission colors were obtained by triply doping Eu(3+), Tb(3+) and Tm(3+) activators in a single host and adjusting their relative ratio.

Mg1.5Lu1.5Al3.5O1.5O12:Ce3+,Mn2+, a novel garnet phosphor was synthesized by solid state reaction. The obtained samples can be excited efficiently by the blue light and exhibit varied hues from green-yellow through yellow and eventually to orange by tuning the relative proportion of Ce3+/Mn2+.

In this paper, the color point tuning of Y3Al5O12 : Ce3+ phosphor has been realized by the incorporation of Mn2+–Si4+. The Mn2+ ions occupy the dodecahedral crystallographic Y3+ site, while the Si4+ ions substitute the tetrahedral Al3+ crystallographic site in the obtained powder. Under 450 nm excitation, the YAG : Ce3+,Mn2+,Si4+ samples exhibit the typical yellowish-green emission band of the Ce3+ ions, as well as an orange emission band of the Mn2+ ions. Furthermore, the intensity ratio of the orange/yellowish-green band can be enhanced through the increase of Mn2+–Si4+ content. The intense orange emission band of the Mn2+ ions is attributed to the effective energy transfer from the Ce3+ to Mn2+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The related mechanism was demonstrated to be the electric dipole–quadrupole interaction based on the Inokuti–Hirayama theoretical model, and critical distance is calculated to be 8.6 A by the spectral overlap method.