Yongchao Jia

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.

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.

A tunable warm-white-light Sr3Gd(PO4)3:Eu2+,Mn2+ phosphor system for LED-based solid-state lighting

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.

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+.

Structure and photoluminescence properties of novel Ca2NaSiO4F:Re (Re = Eu2+, Ce3+, Tb3+) phosphors with energy transfer for white emitting LEDs

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.

Crystal structure and luminescent properties of a novel high efficiency blue-orange emitting NaCa2LuSi2O7F2:Ce3+,Mn2+ phosphor for ultraviolet 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.