Zhendong Hao

Tunable full-color-emitting Ca3Sc2Si3O12:Ce3+, Mn2+ phosphor via charge compensation and energy transfer

A tunable full-color-emitting Ca(3)Sc(2)Si(3)O(12):Ce(3+), Mn(2+) (CSS:Ce(3+),Mn(2+)) phosphor is obtained by addition of doped ions as charge compensation. White LEDs with high R(a) (> 90) are achieved using the single CSS:Ce(3+),Mn(2+) phosphor.

Tunable full-color emitting BaMg2Al6Si9O30:Eu2+,Tb3+,Mn2+phosphors based on energy transfer

A series of single-phase full-color emitting BaMg(2)Al(6)Si(9)O(30):Eu(2+), Tb(3+), Mn(2+) phosphors has been synthesized by solid-state reaction. Energy transfer from Eu(2+) to Tb(3+) and Eu(2+) to Mn(2+) in BaMg(2)Al(6)Si(9)O(30) host matrix is studied by luminescence spectra and energy-transfer efficiency and lifetimes. The wavelength-tunable white light can be realized by coupling the emission bands centered at 450, 542, and 610 nm ascribed to the contribution from Eu(2+) and Tb(3+) and Mn(2+), respectively. By properly tuning the relative composition of Tb(3+)/Mn(2+), chromaticity coordinates of (0.31, 0.30), high color rendering index R(a) = 90, and correlated color temperature (CCT) = 5374 K can be achieved upon excitation of UV light. Thermal quenching properties reveal that BaMg(2)Al(6)Si(9)O(30): Eu(2+), Tb(3+), Mn(2+) exhibits excellent characteristics even better than that of YAG:Ce. Our results indicate our white BaMg(2)Al(6)Si(9)O(30):Eu(2+), Tb(3+), Mn(2+) can serve as a key material for phosphor-converted light-emitting diode and fluorescent lamps.

White light emitting diode by using α-Ca2P2O7:Eu2+, Mn2+ phosphor

The α-Ca2P2O7:Eu2+, Mn2+ phosphors show two emission bands peaking at around 416 (blue) and 600nm (orange), originating from the allowed f-d transition of Eu2+ and the forbidden T14-A16 transition of Mn2+, respectively, under near ultraviolet (UV) excitation at 400nm. Spectroscopy and fluorescence lifetime measurements demonstrate that energy transfer from Eu2+ to Mn2+ performs with transfer efficiency as high as 65% for Mn2+ concentration of 12mol%. The authors have fabricated a white light emitting diode (LED) through the integration of GaN near-UV chip and two phosphor blends (α-Ca2P2O7:Eu2+, Mn2+ blue-orange phosphor and Ba2SiO4:Eu2+ green phosphor) into a single package. The white LED shows color rendering index of 78, luminescent efficiency of 9lm∕W, and low color point variation against forward-bias currents.

Generating yellow and red emissions by co-doping Mn2+ to substitute for Ca2+ and Sc3+ sites in Ca3Sc2Si3O12:Ce3+ green emitting phosphor for white LED applications

We report luminescence properties of Ce3+ and Mn2+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnets. It is observed that Mn2+ may not only occupy Ca2+ sites to generate a yellow emission (Mn2+(I)) at 574 nm but also Sc3+ sites to generate a red emission (Mn2+(II)) at 680 nm. Considerable Mn2+ substitution for Sc3+ can be performed through balancing their charge difference by introducing a trivalent rare earth ion, such as La3+ and Ce3+, to replace Ca2+. Meanwhile, remarkable energy transfer from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) can occur, making tunable color and white light emission available in CSS:Ce3+,Mn2+ upon blue excitation into Ce3+. White LEDs combined by CSS:Ce3+,Mn2+ phosphors and blue LED chips are fabricated. A CSS:0.03Ce3+,0.2Mn2+ phosphor with deficient red emission is enriched in red by increasing Ce3+ concentration to 0.1, which leads to increase of Mn2+(II) number in case of charge compensation by more Ce3+ ions. Consequently, the color rendering index of the white LEDs is improved from 64 to 76. The results of this work indicate that CSS:Ce3+,Mn2+ garnet could be a promising single phase phosphor for white LEDs.

Generation of broadband emission by incorporating N3− into Ca3Sc2Si3O12 : Ce3+ garnet for high rendering white LEDs

Adding Si3N4 into green emitting Ca3Sc2Si3O12 : Ce3+ garnet phosphor generates an additionally red emission band peaking around 610 nm that are assigned to Ce3+ ions having N3− in their local coordination. The excitation spectrum of the red band consists of not only a distinct band at 510 nm of itself but also an intense blue band at 450 nm that belongs to the typical Ce3+ ions with green emission, indicating a notable energy transfer from the green emitting Ce3+ ions to the red ones. The energy transfer significantly enables the achievement of a broad emission spectrum covering a red and green spectral region suitable for generating white light upon a blue light-emitting diode (LED) excitation. The decay patterns of the red and green fluorescence are discussed in relation to the effect of energy transfer. A white LED with high color rendering of 86 and low correlated color temperature of 4700 K is fabricated using the present single garnet phosphor.

Color control and white light generation of upconversion luminescence by operating dopant concentrations and pump densities in Yb3+, Er3+ and Tm3+ tri-doped Lu2O3 nanocrystals

We synthesized a series of Yb3+, Er3+ and Tm3+ tri-doped Lu2O3 nanocrystals with various dopant concentrations by the hydrothermal approach. Due to a unique electronic state at the top of the valence band, Lu2O3 based materials exhibit intense upconversion luminescence involving 1G4 → 3H6 of Tm3+ in blue, (2H11/2, 4S3/2) → 4I15/2 in green and 4F9/2 → 4I15/2 in red of Er3+ upon near infrared excitation at 980 nm. The variation of upconversion spectra and color points with dopant concentrations and pump densities are studied in detail on the basis of energy transfer processes. An ideal white upconversion light with color coordinates of (0.327, 0.339) is obtained by controlling the intensity of red, green, and blue emission in Lu1.906Yb0.08Er0.008Tm0.006O3nanocrystals under a pump density of 8 W cm−2. Based on the present experimental data, we may predict the dopant concentrations and pump densities for any color point within or around the white light region in the tri-doped Lu2O3 nanocrystals.

Interionic energy transfer in Y3Al5O12:Ce3+, Pr3+ phosphor

We present an investigation of dynamical processes of nonradiative energy transfer (ET) between Ce3+ and Pr3+, and between Pr3+ ions in Y3Al5O12:Ce3+, Pr3+ phosphor. Photoluminescence spectroscopy and fluorescence decay patterns are studied as a function of Pr3+ and Ce3+ concentrations. The analysis based on Inokuti–Hirayama model indicates that the ET from the lowest 5d state of Ce3+ to the D12 state of Pr3+, and the quenching of the D12 state through a cross relaxation involving Pr3+ ions in the ground state are both governed by electric dipole–dipole interaction. An increase in the Ce3+–Pr3+ ET rate followed by the enhanced red emission line of Pr3+ relative to the yellow emission band of Ce3+ on only increasing Ce3+ concentration is observed. This behavior is attributed to the increase in the spectral overlap integrals between Ce3+ emission and Pr3+ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce3+ concentration while the red line dose not move. For C...

Blue-Emitting K2Al2B2O7:Eu2+ Phosphor with High Thermal Stability and High Color Purity for Near-UV-Pumped White Light-Emitting Diodes

Novel blue-emitting K2Al2B2O7:Eu(2+) (KAB:Eu(2+)) phosphor was synthesized by solid state reaction. The crystal structural and photoluminescence (PL) properties of KAB:Eu(2+) phosphor, as well as its thermal properties of the photoluminescence, were investigated. The KAB:Eu(2+) phosphor exhibits broad excitation spectra ranging from 230 to 420 nm, and an intense asymmetric blue emission band centered at 450 nm under λex = 325 nm. Two different Eu(2+) emission centers in KAB:Eu(2+) phosphor were confirmed via their fluorescence decay lifetimes. The optimal concentration of Eu(2+) ions in K2-xEuxAl2B2O7 was determined to be x = 0.04 (2 mol %), and the corresponding concentration quenching mechanism was verified to be the electric dipole-dipole interactions. The PL intensity of the nonoptimized KAB:0.04Eu(2+) phosphor was measured to be ∼58% that of the commercial blue-emitting BaMgAl10O17:Eu(2+) phosphor, and this phosphor has high color purity with the CIE coordinate (0.147, 0.051). When heated up to 150 °C, the KAB:0.04Eu(2+) phosphor still has 82% of the initial PL intensity at room temperature, indicating its high thermal stability. These results suggest that the KAB:Eu(2+) is a promising candidate as a blue-emitting n-UV convertible phosphor for application in white light emitting diodes.

Blue-Green-Emitting Phosphor CaSc2O4 : Tb3 + : Tunable Luminescence Manipulated by Cross-Relaxation

Blue-green CaSc2O4:Tb3+ phosphors have been prepared by solid-state reaction. Under 254 or 276 nm light excitation, both blue and green emissions are observed, which are attributed to the characteristic 4f-4f transitions (D-5(3,4)-F-7(J), J = 6, 5, 4, 3) of Tb3+. The cross-relaxation from D-5(3) to D-5(4) states are investigated by spectroscopic and dynamic measurements. The luminescent color of CaSc2O4:Tb3+ can be tuned from blue to green by manipulating the cross-relaxation. Moreover, efficient white light is generated for fluorescence lamps by blending the blue-green CaSc2O4:Tb3+ with a red CaSc2O4:Eu3+ phosphor. (c) 2009 The Electrochemical Society. [DOI: 10.1149/1.3060382] All rights reserved.

Enriching red emission of Y 3 Al 5 O 12 : Ce 3+ by codoping Pr 3+ and Cr 3+ for improving color rendering of white LEDs

Triply doped Y3Al5O12: Ce3+, Pr3+, Cr3+ phosphors are prepared by solid state reaction. The emission spectra are enriched in the red region with the luminescence of both Pr3+ and Cr3+ through Ce3+ → Cr3+ and Ce3+ → Pr3+ → Cr3+ energy transfers. The properties of photoluminescence and fluorescence decay indicates larger macroscopic Ce3+ → Cr3+ transfer rates in the triply doped phosphors in comparison to Ce3+ and Cr3+ doubly doped one, reflecting the effect of competition between Ce3+ → Cr3+ and Ce3+ → Pr3+ transfers. White LEDs fabricated using the triply doped phosphor coated on blue LED chips show a color rendering index of 81.4 higher than that either using Ce3+ and Cr3+ doubly doped or Ce3+ singly doped phosphor.