Shuchao Xu

Luminescence and energy transfer of Eu2+/Tb3+/Eu3+ in LiBaBO3 phosphors with tunable-color emission

A series of LiBaBO3:RE (RE = Eu2+/Tb3+/Eu3+) phosphors have been synthesized using the high-temperature solid-state reaction method. The X-ray diffraction (XRD), emission spectra, excitation spectra, decay lifetimes, and diffuse reflection spectra were utilized to characterize the phosphors. The as-prepared samples have been characterized via XRD measurement and showed that Eu2+/Tb3+/Eu3+ can be efficiently doped into the host. The obtained phosphors can emit different colors of light when doping with different activators. The energy transfer from Tb3+ to Eu3+ occurs in LiBaBO3:0.03Eu3+,yTb3+ prepared in the air. While an abnormal reduction phenomenon was reported when Eu and Tb ions were co-doped in LiBaBO3 and prepared in an inferior reductive atmosphere, which showed tunable-color from blue to red based on energy transfer of Eu2+ → Tb3+ → Eu3+ ions. And the energy transfer not only can occur between Eu2+ and Tb3+ ions, but also between Tb3+ and Eu3+ ions. All these results reveal that Tb3+ can play the role of storing the energy for Eu3+, and LiBaBO3 may be a potential candidate phosphor for LEDs.

Tunable blue-green emitting and energy transfer of a Eu2+/Tb3+ codoped Sr3La(PO4)3 phosphor for near-UV white LEDs

A series of Eu2+ and Tb3+ doped Sr3La(PO4)3 phosphors have been synthesized via the high-temperature solid-state reaction method. X-ray diffraction (XRD) patterns, luminescence spectra including temperature-dependent luminescence spectra, and fluorescence decay lifetimes have been used to characterize the as-prepared samples. Under ultraviolet excitation, Sr3La(PO4)3:Eu2+ shows a strong blue emission around 418 nm and a shoulder centered at 500 nm, which is based on the substitution of two kinds of Sr2+ sites by Eu2+ ions (Eu1 and Eu2). Sr3La(PO4)3:Tb3+ shows characteristic emission lines of Tb3+ under 376 nm excitation. For Sr3La(PO4)3:Eu2+,Tb3+ phosphor, similar excitation spectra monitored at 418, 500 and 545 nm have been observed, which illustrates the possibility of energy transfer from Eu2+ to Tb3+ ions. Compared with the Tb3+ singly doped phosphor, the codoped phosphors have more intense absorption in the n-UV range and stronger emission of the Tb3+ ions, which are attributed to the effective energy transfer from the Eu2+ to Tb3+ ions. The variations in the emission spectra, emission color and decay lifetimes further demonstrate the existence of energy transfer from Eu2+ to Tb3+ ions under ultraviolet excitation. For Eu1 and Eu2, the energy transfer mechanism has been confirmed to be quadrupole–quadrupole and dipole–quadrupole interaction, respectively. The results can be validated via the agreement of critical distances obtained from the concentration quenching (21.62 A). These results show that the phosphors may possess potential application in ultraviolet-based white light-emitting diodes.

Substituting Different Cations in Tuning of the Photoluminescence in Ba3Ce(PO4)3.

An attempt has been made to explore how the luminescence properties change when rare-earth elements are substituted for different cations in the host. We synthesized Eu(2+)-doped Ba3Ce(PO4)3 via a high-temperature solid-state reaction process, substituting for Ba(2+) and Ce(3+) ions and naming them Ba3Ce(1-x)(PO4)3:xEu(2+) and Ba(3-y)Ce(PO4)3:yEu(2+), respectively. The structure, X-ray diffraction with Rietveld refinements, reflectance spectra, and luminescence characterization of the phosphor are measured to explore the difference of substituting for different ions. In order to explain why all of the emission peaks containing the highest peak and the fitting values of Ba3Ce(1-x)(PO4)3:xEu(2+) are shorter than those of Ba(3-y)Ce(PO4)3:yEu(2+) (when x= y), we built a model by N, which represents the surrounding environment. This mechanism is predicted to be general to Eulytite-type orthophosphates and will be useful in tuning optical and other properties whose structural disorder influences the crystallization and is sensitive to local coordination environments. Substituting different cations in tuning of the red shift, widening of the full width at half-maxima (fwhm), and thermal quenching were also observed.

Single-phase white-emitting phosphors Ba3Ce(1−x−y)(PO4)3:xTb3+,yMn2+ and Ba3Ce(1−x−z)(PO4)3:xTb3+,zSm3+: structure, luminescence, energy transfer and thermal stability

A series of Ba3Ce(1−x−y)(PO4)3:xTb3+,yMn2+ and Ba3Ce(1−x−z)(PO4)3:xTb3+,zSm3+ phosphors were synthesized by a high temperature solid-state reaction. X-ray diffraction, luminescence and decay curves were used to characterize the phosphors. All the synthesized phosphors crystallized in the cubic unit cell with I3d space group. Energy can be transferred from Ce3+ to Tb3+/Mn2+/Sm3+ in Ba3Ce(1−x)(PO4)3:xTb3+, Ba3Ce(1−y)(PO4)3:yMn2+, and Ba3Ce(1−z)(PO4)3:zSm3+ phosphors. Furthermore, the color of these phosphors can turn from cyan to green, blue to red, and cyan to pale pink. When Ba3Ce(PO4)3 was co-doped with Tb3+ and Mn2+/Sm3+, Tb3+ could also transfer part of its energy to Mn2+/Sm3+, and more importantly, a white emission can be achieved based on this energy transfer. The phosphors exhibited a good thermal stability, with correlated color temperatures of up to 3301 K, and a quantum efficiency as high as 51.2%. These results revealed that we managed to obtain good white emitting phosphors by co-doping Ba3Ce(PO4)3 with Tb3+ and Mn2+/Sm3+.

A series of tunable emission phosphors of Sm3+, Eu3+ and Mn2+ doped Ba3Tb(PO4)3: luminescence and energy transfer

A series of activator Sm3+, Eu3+, Mn2+ ion doped Ba3Tb(PO4)3 phosphors with tunable emitting color were synthesized via the high temperature solid state method. X-ray diffraction, luminescence and fluorescent decay curves were used to characterize the phosphors. The obtained powder crystallizes as a cubic unit cell with the space group Ī43d. Under 377 nm excitation of Tb3+, Ba3Tb(PO4)3:Sm3+ not only presents 5D4–7F6–3 of Tb3+ emission lines but also 4G5/2–6H5/2–9/2 of Sm3+ orange emission lines, Ba3Tb(PO4)3:Eu3+ contains the emission lines of Tb3+ and Eu3+ (5D0–7F1–4), and Ba3Tb(PO4)3:Mn2+ exhibits the emission lines of Tb3+ and 4T1–6A1 orange emission band of Mn2+. In addition, the intensities of the red or orange-red emission can be enhanced by tuning the Sm3+, Eu3+ and Mn2+ contents. The intense emission intensities of Sm3+, Eu3+ and Mn2+ ions are attributed to the efficient energy transfer from Tb3+ to Sm3+, Eu3+ and Mn2+ ions, respectively, which have been justified through the luminescence spectra and fluorescence decay dynamics. The energy transfer mechanism was demonstrated to be the electric dipole–dipole interaction. For Ba3Tb(PO4)3:Sm3+, Ba3Tb(PO4)3:Eu3+ and Ba3Tb(PO4)3:Mn2+, the best quantum efficiencies are 41.6%, 70.3% and 49.8%, respectively. The properties of the phosphors indicate that they may have potential application in UV-pumped white light emitting diodes.

Broadening emission band of Ba 2 B 2 O 5 : Dy 3+ by codoping Ce 3+ as sensitizer and its application to white LEDs

In order to achieve broad-band white emitting phosphor, Ce3+/Dy3+ codoped Ba2B2O5 were synthesized by a solid-state method, and the luminescence property and energy transfer were discussed in detail. Dy3+ doped Ba2B2O5 shows white emission, and the two narrow peaks which are assigned to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ions, respectively. When codoped Ce3+ as sensitizer, the broad-band white emission can be obtained by the energy transfer from Ce3+ to Dy3+ ions in Ba2B2O5, and the mechanism is the dipole-dipole interaction. And the CIE coordinates can be tuned from (0.2501, 0.2323) to (0.3422, 0.3799) by increase Dy3+ content. The emission peak blue-shift of Ce3+ ions in Ba2B2O5:Ce3+, Dy3+ was observed from the thermal spectra, and the mechanism was analyzed. A white light emitting diodes (LEDs) can be fabricated Ba2B2O5:Ce3+, Dy3+ with 380nm chip, and the results show that the phosphor may be a potential application in this field.

Zn2−aGeO4:aRE and Zn2Ge1−aO4:aRE (RE = Ce3+, Eu3+, Tb3+, Dy3+): 4f–4f and 5d–4f transition luminescence of rare earth ions under different substitution

Generally, luminescent properties of rare earth ions doped host can be tuned by controlling the host composition, that is, when substituted for different cations of host, the rare earths ions can present different characteristics. In this research, Zn2−xGeO4:xCe3+ and Zn2Ge1−xO4:xCe3+ can show two different emission bands due to the 5d–4f transitions of Ce3+ ions. Moreover, the CIE chromaticity coordinates and the luminescence photographs of Zn2−xGeO4:xCe3+ and Zn2Ge1−xO4:xCe3+ exhibit different characteristics. The emission bands appear blueshift and redshift due to the combination of crystal field splitting and nephelauxetic effect. However, for Zn2−aGeO4:aR and Zn2Ge1−aO4:aR (R = Eu3+, Tb3+, Dy3+), the 4f–4f characteristic transitions of Tb3+, Eu3+ and Dy3+ are observed, and the emission and excitation peaks are not influenced by the crystal field.

Inducing tunable host luminescence in Zn 2 GeO 4 tetrahedral materials via doping Cr 3

Zn2GeO4 consisting of tetrahedron, and it is a self-luminescent material due to the presence of the native defects and shows a bluish white emission excited by ultraviolet. Although Cr3+ doped in a tetrahedron generally cannot show luminescence, in this research, new defects are formed as Cr3+ doped in Zn2GeO4, hence a green emission band can be obtained. Meanwhile, the intensity of host emission is also decreased. Therefore, Zn2GeO4:Cr3+ are synthesized using a high-temperature solid-phase method. Thermoluminescence (TL) and luminescence decay curves are used to investigate the variation of native defects. The emission colour can be tuned from bluish white to green when Cr3+ doped in Zn2GeO4. This result has guidance for controlling the native emission of self-luminescent material.

Tuning of luminescence properties by controlling an aid-sintering additive and composition in Na(Ba/Sr/Ca)PO4:Eu2+ for white LEDs

A series of Na(Ba/Sr/Ca)PO4:Eu2+ phosphors were prepared via a high-temperature solid-state reaction method. When the phase of NaCaPO4:Eu2+ was pure, the luminescence of Eu2+ was enhanced by doping the sintering-aid additive NaCl (t), and it showed a maxima at t = 0.03. For NaCaPO4:Eu2+ with 0.03NaCl, the XRD patterns, and emission and decay spectra demonstrated that Eu2+ ions occupied two different Ca sites with different coordination (i.e., eight and seven coordination). Therefore, two green emission bands at 510 and 542 nm were observed, and the emission band ranging from 480 to 510 nm had a weaker intensity. To obtain a cyan-broad emission, Ba2+ or Sr2+ were introduced into NaCaPO4:0.01Eu2+. The substitution of small Ca2+ ions by large Ba2+ or Sr2+ ions induced a decreased crystal field splitting of Eu2+ ions, which resulted in various full width at half maximum and a blue shift. The colors varied from green (0.1996, 0.4380) to blue (0.1578, 0.0978) under the same excitation. Overall, the phosphor has promising applications for use in white LEDs.

Using rare earth ions to improve the luminescence properties of the defect-related luminescent material Zn3Al2Ge2O10

Herein, Zn3Al2Ge2O10 was synthesized by a high-temperature solid-state method, and a weak white emission ranging from 350 to 600 nm was observed. To enhance the white emission intensity of Zn3Al2Ge2O10, rare earth ions (Eu3+, Ce3+, Dy3+, and Tb3+) were introduced into Zn3Al2Ge2O10. The results show that the white emission intensity of Zn3Al2Ge2O10 is enhanced by doping rare earth ions, which is ascribed to the increased oxygen vacancy . Especially, Eu3+ ions can effectively enhance the white emission intensity of Zn3Al2Ge2O10 as compared to other rare earth ions (Ce3+, Dy3+, and Tb3+) when doped in Zn3Al2Ge2O10, and the intensity is maximum when the doping concentration reaches 6 mol%. The results indicate that the luminescence properties of the defect-related luminescent material Zn3Al2Ge2O10 can be improved by doping rare earths ions.