Wenzhen Lv

Tunable Color of Ce3+/Tb3+/Mn2+-Coactivated CaScAlSiO6 via Energy Transfer: A Single-Component Red/White-Emitting Phosphor

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.

Tunable Blue-Green-Emitting Ba3LaNa(PO4)3F:Eu2+,Tb3+ Phosphor with Energy Transfer for Near-UV White LEDs

A series of Eu(2+) and Eu(2+)/Tb(3+) activated novel Ba3LaNa(PO4)3F phosphors have been synthesized by traditional solid state reaction. Rietveld structure refinement of the obtained phosphor indicates that the Ba3LaNa(PO4)3F host contains three kinds of Ba sites. The photoluminescence properties exhibit that the obtained phosphors can be efficiently excited in the range from 320 to 430 nm, which matches perfectly with the commercial n-UV LED chips. The critical distance of the Eu(2+) ions in Ba3LaNa(PO4)3F:Eu(2+) is calculated and the energy quenching mechanism is proven to be dipole-dipole interaction. Tunable blue-green emitting Ba3LaNa(PO4)3F:Eu(2+),Tb(3+) phosphor has been obtained by co-doping Eu(2+) and Tb(3+) ions into the host and varying their relative ratios. Compared with the Tb(3+) singly doped phosphor, the codoped phosphors have more intense absorption in the n-UV range and stronger emission of the Tb(3+) ions, which are attributed to the effective energy transfer from the Eu(2+) to Tb(3+) ions. The energy transfer from the Eu(2+) to Tb(3+) ions is demonstrated to be a dipole-quadrupole mechanism by the Inokuti-Hirayama (I-H) model. The Eu(2+) and Tb(3+) activated phosphor may be good candidates for blue-green components in n-UV white LEDs.

Sr3GdNa(PO4)3F:Eu2+,Mn2+: a potential color tunable phosphor for white LEDs

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 Novel Efficient Mn4+ Activated Ca14Al10Zn6O35 Phosphor: Application in Red-Emitting and White LEDs

A new, highly efficient deep red-emitting phosphor Ca14Al10Zn6O35:Mn(4+) was developed as a component of solid-state white light-emitting diodes (LEDs). The structural and optical characterization of the phosphor is described. The phosphor exhibits strong emission in the range of 650-700 nm when excited by 460 nm excitation, with a quantum efficiency approaching 50%. Concentration dependence of Mn(4+) luminescence in Ca14Al10Zn6O35:Mn(4+) is investigated. Attempts to understand the thermal stability on the basis of the thermal quenching characteristics of Ca14Al10Zn6O35:Mn(4+) is presented. The results suggest that phosphors deriving from Ca14Al10Zn6O35:Mn(4+) have potential application for white LEDs. In addition, influence of cation substitution on the luminescence intensity of these phosphors is elucidated.

Color point tuning of Y3Al5O12:Ce3+ phosphor via Mn2+-Si4+ incorporation for white light generation

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.

Ba1.3Ca0.7SiO4:Eu2+,Mn2+: A Promising Single-Phase, Color-Tunable Phosphor for Near-Ultraviolet White-Light-Emitting Diodes

In this paper, Eu(2+)-doped and Eu(2+)/Mn(2+)-codoped Ba1.3Ca0.7SiO4 phosphors were synthesized by means of a conventional solid-state reaction process. The single-phase purity was checked by means of X-ray diffraction and the Rietveld method. Under excitation at 390 nm, the emission spectra of the Eu(2+)-doped phosphors exhibit a broad-band emission centered at 500 nm caused by the electric dipole allowed transition of the Eu(2+) ions. The emission spectra of codoped phosphors show one more broad emission centered at 600 nm attributable to the transitions from the (4)T1((4)G) → (6)A1((6)S) of Mn(2+) ions. The luminescent color of the codoped phosphors can be easily adjusted from blue to red with variation of the Mn(2+) content. The energy transfer mechanism from the Eu(2+) to Mn(2+) ions in Ba1.3Ca0.7SiO4 phosphors has been confirmed to be the resonant type via dipole-quadrupole interaction, and the critical distance has been calculated quantitatively. All these results demonstrate that the Eu(2+)/Mn(2+)-codoped Ba1.3Ca0.7SiO4 phosphors can be a promising single-phase, color-tunable phosphor for near-UV white-light-emitting diodes after a further optimization process. Additionally, a great red shift from 593 to 620 nm has been observed following the increase of Mn(2+) content, and the phenomenon has been discussed in relation to the changes in the crystal field surrounding the Mn(2+) ions and the exchange interactions caused by the formation of Mn(2+) pairs.

Generation of orange and green emissions in Ca2GdZr2(AlO4)3:Ce3+, Mn2+, Tb3+ garnets via energy transfer with Mn2+ and Tb3+ as acceptors

Utilizing Mn2+ and Tb3+ ions as energy-transfer acceptors, we report a series of emission color-tunable Ca2GdZr2(AlO4)3:Ce3+, Mn2+, Tb3+ aluminate garnets. Incorporating Mn2+ and Tb3+ into Ca2GdZr2(AlO4)3:Ce3+ phosphor generates an orange emission band peaking at 572 nm and a green line peaking at 550 nm. The energy transfers from Ce3+ to Mn2+ and Ce3+ to Tb3+ ions are deduced from the spectral overlap between the Ce3+ emission and Mn2+/Tb3+ excitation spectra. Fluorescence decay patterns are studied as a function of Mn2+ and Tb3+ concentration. The calculated values based on the luminescence dynamical process indicate that the intensity ratios of the orange to green bands as a function of Mn2+ concentration are in good agreement with those obtained directly from the emission spectra. We have demonstrated that the color emission as well as the luminescence external quantum yield (20.4–48.9%) can be tuned by precisely controlling the content of Ce3+, Mn2+, and Tb3+. The energy transfer significantly enables the achievement of a broad emission spectrum covering an orange spectral region. It is suitable for near-UV light-emitting diode (LED) excitation.

3D-hierarchical Lu2O2S:Eu3+ micro/nano-structures: controlled synthesis and luminescence properties

Several three-dimensional (3D) hierarchical architectures of Lu2O2S:Eu3+ have been successfully synthesized via a simple solvothermal method with polyvinylpyrrolidone (PVP) as surfactant, followed by a subsequent calcination process. The as-prepared products were well characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and photoluminescence (PL) spectra. The results reveal that the morphologies of precursors can be tuned by altering pH value of the reaction system. Detailed investigation indicates that the formations of different micro-structures are dominated by different growth mechanisms. The as-formed precursors could transform into Lu2O2S:Eu3+ with their original hierarchical structures maintained. Under ultraviolet (UV) excitation, the Lu2O2S:Eu3+ micro-architectures exhibit strong red emission corresponding to the 5D0→7F2 transition of the Eu3+ ions. Furthermore, the dependence of Lu2O2S:Eu3+ luminescence performance on different morphologies has been involved in the present work.

Eu2+ & Mn2+-Coactivated Ba3Gd(PO4)(3) Orange-Yellow-Emitting Phosphor with Tunable Color Tone for UV-Excited White LEDs

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.

Mg1.5Lu1.5Al3.5Si1.5O12:Ce3+,Mn2+: A novel garnet phosphor with adjustable emission color for blue light-emitting diodes

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+.