Energy Transfer Of Ce3 Research Articles

Fluorescence properties and energy transfer investigation of novel Li2Al2B2O7:Ce3+, Tb3+ phosphors via combustion synthesis

Energy transfer in Ce3+ and Tb3+ co-doped Li2Al2B2O7 (LABO) phosphors were synthesized by using the solution combustion method. The phase and photoluminescent properties of Ce3+ and Tb3+ co-doped LABO phosphors were investigated by using the powder X-ray diffraction and photoluminescence emission and excitation spectra. The results show that under the excitation of 357 nm wavelengths, it exhibited blue emission corresponding to the f–d transition of Ce3+ ions and green emission bands corresponding to the f–f transition of Tb3+ ions, respectively. Overlapping observed between the emission spectrum of Ce3+ ion and the excitation spectrum of Tb3+ ion due to energy transfer occurred from Ce3+ to Tb3+ in LABO host. The energy transfer efficiency from Ce3+ ion to Tb3+ ion was also calculated to be 68 %. Furthermore, thermal analysis, concentration quenching and critical distance of LABO:Ce3+,Tb3+ phosphors were also discussed.

Complement of Special Relativity and Limitation of General Relativity

<p class="1Body">For a set of forces being in equilibrium, the equilibrium state will not vary from one observer to another. This generally acknowledged fact has been called as the Force Equilibrium Invariance Axiom. On the basis of this axiom, the force transformation formula can be derived when an object is in motion, so that the force, length, time and mass can be calculated as per the basic transformation formula for the special relativity. According to the results of experimental analysis obtained by J.C. Hafele and R.E. Keating, the concepts of absolute time delay and relative time delay have been put forward herein, so as to solve any problems on the traveling velocity and records of any object being in motion at the real-time. For the properties of the force, the force applied on an object being accelerated will be deemed as the energy transfer force, while the universal gravitation will be deemed as the applied force of field. Both forces have the different basic properties. It is unscientific to consider both forces being the same properties. Based on the Force Equilibrium Invariance Axiom, it is deduced that the gravitational mass can only be the constant irrelevant to the motion of an object. Therefore, the principle of equivalence will not be tenable in theory. Only if the motion velocity of an object is very small relative to the velocity of light, can the principle of equivalence be deemed being approximately tenable. Under this condition, the general relativity can be only consistent with the practical deducing principle. However, if the motion velocity of an object is relatively large, there will be a significant difference between the constant gravitational mass and the inertial mass; as a result, there may be a deviation between the inference on the general relativity and the practical deducing principle. Take the Black Hole as an example. Even if the Black Hole is made almost completely of neutrons, its actual volume is one million times greater than its theoretical volume. Therefore, it is concluded that the Black Hole cannot be deemed as the substance composed of real atoms. It also shows accordingly that, according to the general relativity of theoretical source of Black Hole, the analysis results obtained when an object is in motion at high-velocity can not conform to the reality.</p>

Temperature Dependent Energy Transfer in Ce3+-Yb3+ Co-Doped YAG Phosphors

Ce3+-Yb3+ co-doped Y3Al5O12 (YAG) phosphors were prepared, and their photoluminescence spectra, photoluminescence excitation spectra and fluorescence decay curves were measured at different temperatures from 8 K to 300 K. Experimental results show that, besides thermal quenching effect, the energy transfer is also the mechanism for the temperature dependence of the Yb3+ emission. A photo-induced Ce-O-Yb charge transfer state model is proposed to explain the variation of the emission with the temperature. The decay curves of the co-doped YAG phosphors at different temperatures can also be explained by the model.

Tunable luminescence and energy transfer of Ce3+/Eu2+/Mn2+-tridoped Sr8MgLa(PO4)7 phosphor for white light LEDs

A series of Ce3+/Eu2+/Mn2+-tridoped Sr8MgLa(PO4)7 phosphors were synthesized by a solid state reaction. The crystal structure and luminescence properties were characterized by X-ray diffraction (XRD), photoluminescence emission spectroscopy (PL), and X-ray photoelectron spectroscopy (XPS). Effective energy transfer occurs from Ce3+ to Eu2+ and from Ce3+/Eu2+ to Mn2+ in Sr8MgLa(PO4)7 host. Under near ultraviolet (UV) excitation, Sr8MgLa(PO4)7:Eu2+,Mn2+ phosphor exhibits the yellow–green emission of the Eu2+ ions and the red emission of the Mn2+ ions and the emission color can be tuned from yellow–green to orange with variation of the Mn2+ content. Co-doping Ce3+ ions is proved to be an effective approach to enhance both the emissions of Eu2+ and Mn2+ ions. A cascade model of energy transfer Ce3+ → Eu2+ → Mn2+ was put forward to explain the ET process in SMLP:Ce3+,Eu2+,Mn2+ system. Additionally, an increase in the number of luminescent centers (Eu2+) on Ce doping may be other causes of the enhanced Eu2+ luminescence. The developed Sr8MgLa(PO4)7:Ce3+,Eu2+,Mn2+ phosphors could have potential applications in near UV- pumped white LEDs.

Near-infrared multi-wavelengths long persistent luminescence of Nd3+ ion through persistent energy transfer in Ce3+, Cr3+ co-doped Y3Al2Ga3O12 for the first and second bio-imaging windows

We developed a persistent phosphor of Y3Al2Ga3O12 doped with Nd3+, Ce3+, Cr3+ ions (YAGG:Nd-Ce-Cr) exhibiting long (>10 h) persistent luminescence at multi-wavelengths of around 880, 1064, and 1335 nm due to f-f transitions of Nd3+ and at 505 nm due to Ce3+:5d1→4f transition. The intense near-infrared (NIR) persistent luminescence bands from Nd3+ match well with the first (650–950 nm) and second (1000–1400 nm) bio-imaging windows. The NIR persistent radiance of the YAGG:Nd-Ce-Cr phosphor (0.33 × 10−1 mW/Sr/m2) at 60 min after ceasing blue light illumination was over 2 times higher than that of the widely used ZnGa2O4:Cr3+ red persistent phosphor (0.15 × 10−1 mW/Sr/m2).

Photoluminescence and Energy Transfer of Ce3+, Tb3+, and Eu3+ Doped KBaY(BO3)2 as Near-Ultraviolet-Excited Color-Tunable Phosphors

A series of Ce3+, Tb3+ codoped and Ce3+, Tb3+, Eu3+ tridoped KBaY(BO3)2 (KBYB) phosphors are synthesized by the solid-state method. The codoped and tridoped phosphors absorb near-ultraviolet (NUV) light through 4f–5d transitions of Ce3+, followed by blue emissions of Ce3+ along with sensitized Tb3+green and Eu3+red emission, respectively. The energy-transfer process is discussed in terms of both the luminescence spectra and decay curves. Because of the long Y–Y distance in KBYB structure, high Tb3+ content is required to form a Tb3+ bridge for a complete Ce3+ → Tb3+ → Eu3+ energy transfer. By controlling the Ce3+/Tb3+/Eu3+ ratio, the color of the phosphor varied from blue (0.173, 0.087) to green (0.341, 0.570) and eventually to red (0.589, 0.374). The results indicated that the codoped and tridoped KBYB exhibited broadband NUV absorption and blue–green–red tunable emission, which might serve as down-converted phosphors for NUV light-emitting diodes.

Color tunable emission and energy transfer of Ce3+ and Tb3+ co-doped novel La6Sr4(SiO4)6F2 phosphors with apatite structure

Single-phase La6Sr4(SiO4)6F2: Ce3+, Tb3+ samples with apatite-like structure have been synthesized via solid-state reaction method. The phase structure, luminescence properties, lifetime, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples. Effective energy transfer occurs from Ce3+ to Tb3+ in La6Sr4(SiO4)6F2, which shows more intense Blue-Green light under UV light excitation. In addition, a possible mechanism of the energy-transfer from Ce3+ to Tb3+ ion is also proposed. The critical distance RC of Ce3+ to Tb3+ ions in La6Sr4(SiO4)6F2 host was calculated to be 11.878Å. All the results indicate that La6Sr4(SiO4)6F2:Ce3+, Tb3+ phosphors have potential applications to be used as near UV-convertible phosphors for white light-emitting diodes.

Luminescent properties and energy transfer of Ce3+-activated Li2O–B2O3–Gd2O3 scintillating glasses under VUV–UV and X-ray excitation

Motivated by potential application for neutron detection, novel Ce3+-activated Li2O–B2O3–Gd2O3 scintillating glasses containing neutron-capture elements were synthesized by melt-quenching method. The energy transfer from the host glass to Gd3+ and Ce3+ ions, as well as from Gd3+ to Ce3+ ions are confirmed by VUV–UV spectra. The strongest emission intensity of Ce3+ ions with about 29ns is obtained when the scintillating glass contains a fraction of 0.25mol% CeF3, whose mean distance is estimated to be about 25.63Å.

Energy transfer studies of Ce3+–Mn2+ and Ce3+–Tb3+ in an emitting tunable Mg2Al4Si5O18:Ce3+/Mn2+/Tb3+ phosphor

An emitting tunable Mg2Al4Si5O18:Ce3+/Mn2+/Tb3+ phosphors have been synthesized by high-temperature solid-state reaction technique. In this system, Mg2Al4Si5O18:Ce3+, Mn2+ samples exhibit two dominating bands situated at 430 and 640nm, originating from the Ce3+, Mn2+ ions, respectively. Photoluminescence and energy transfer in Mg2Al4Si5O18:Ce3+, Mn2+ are investigated as a function of Mn2+ concentrations. The intensity ratios of red to blue band as a function of Mn2+ 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 Tb3+, an efficient energy transfer from Ce3+ to Tb3+ 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 Ce3+→Mn2+ and from blue to green via the energy transfer of Ce3+→Tb3+.

Enhanced luminescence properties and energy transfer in Ce3+ and Tb3+ co-doped NaCaBO3 phosphor

A series of color-tunable NaCaBO3: Ce3+, Tb3+ phosphors have been synthesized on the basis of efficient Ce3+→Tb3+ energy transfer. The photoluminescence emission and excitation spectra, the lifetime, and the effect of Tb3+ concentration are investigated in detail. The enhanced photoluminescence of Tb3+ with sharp emission lines could be obtained by the broad excitation band from the allowed 4f–5d absorption of Ce3+ ions. The intensity ratio of blue emission from Ce3+ and green emission from Tb3+ can be tuned by adjusting their concentrations. The energy transfer from Ce3+ to Tb3+ in NaCaBO3 was found to be an electric dipole–quadrupole interaction.

Tunable luminescence and energy transfer properties of a novel Na4Ca4Si6O18:Ce3+,Mn2+ phosphor

By utilizing the energy transfer of Ce3+ to Mn2+, the emitting colors can be adjusted from blue to red in Na4Ca4Si6O18:Ce3+,Mn2+ phosphors.

Luminescence properties and energy transfer of Ce3+/Tb3+ co-doped Ca9La(PO4)5(SiO4)F2 phosphor

Emission-tunable phosphors Ca9La(PO4)5(SiO4)F2:Ce3+,Tb3+ with apatite structure were synthesized by a solid-state reaction. The phase structure, photoluminescence (PL) properties, lifetimes and the PL thermal stability were investigated, respectively. The phosphor exhibited an asymmetric broad-band blue emission (Ce3+) with peak at 403nm and the line-type green emission with peak at 543nm (Tb3+). The varied color of the phosphors from blue to green can be achieved by properly tuning the relative ratio of Ce3+/Tb3+ through the energy transfer from Ce3+ to Tb3+ ions. The critical distance was calculated to be 8.78Å by using the concentration quenching method. When the temperature turned up to 150°C, the emission intensity of Ca9La(PO4)5(SiO4)F2:Ce3+,Tb3+ phosphor was 77% of its initial value at room temperature, which indicated the good thermal stability of the sample. All the properties indicate that the Ca9La(PO4)5(SiO4)F2:Ce3+,Tb3+ phosphor has potential application of color-tunable w-LEDs.

A white emitting phosphor BaMg2(PO4)2:Ce3+, Mn2+, Tb3+: Luminescence and energy transfer

A single-phase white emitting phosphor BaMg2(PO4)2:Ce3+, Mn2+, Tb3+ is synthesized by a high temperature solid-state reaction. There has a spectral overlap between emission band of Ce3+ and excitation bands of Mn2+ and Tb3+, which may support occurrence of energy transfer (ET) from Ce3+ to Mn2+ and Tb3+. Emitting color of BaMg2(PO4)2:Ce3+, Mn2+, Tb3+ can be adjusted from blue to green via ET of Ce3+→Tb3+ and blue to red via ET of Ce3+→Mn2+, respectively. A white light emitting diode (white LED) is fabricated by combining a single-phase white emitting phosphor BMP:3%Ce3+, 5%Mn2+, 3%Tb3+ with a 365nm LED chip, and CIE chromaticity coordinates and correlated color temperature (CCT) of the white LEDs are (0.312, 0.313) and 6217K, respectively. Therefore, as white emitting phosphor, BaMg2(PO4)2:Ce3+/Mn2+/Tb3+ may have potential application in white LEDs.

Synthesis, optical properties, and energy transfer of Ce3+/Tb3+ co-doped MyGdFx (M = Li, Na, K)

Through a solid-state reaction method, the Ce3+/Tb3+ co-doped MyGdFx (M=Li, Na, K; x=3, 4, 6; y=0, 1, 3) system samples have been synthesized by controlling the annealing temperatures and the ratios of raw materials. The samples were characterized by X-ray diffraction (XRD) patterns, photoluminescence (PL) excitation and emission spectra as well as luminescent dynamic decay curves. The experimental results suggest that the LiF is more difficult to react with the prepared material compared that of NaF or KF under similar reaction conditions. The samples crystallized in different crystalline phases. The energy transfer from Ce3+ to Tb3+ or Ce3+ to Gd3+ to Tb3+ has been observed in all the samples. The Ce3+ and Tb3+ present different optical properties for they are sensitive to the local environment. In addition, the deduced lifetime of Tb3+5D4→7F5 transition decreases in the same system samples with the annealing temperature increasing. The deduced lifetime of Tb3+5D4→7F5 also decreases with the increase of the KF concentration in the KF system samples.

Structure and photoluminescence properties of Na2Y2B2O7:Ce3+,Tb3+ phosphors for solid-state lighting application

Novel phosphors of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce3+ emission properties and the crystal structure of Na2Y2B2O7 is built and the result shows that Ce3+ ions occupy two non-equivalent Y3+ sites in the host. The codoping of Tb3+ in Na2Y2B2O7:Ce3+ can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce3+→Tb3+. The energy transfer processes of Ce3+–Ce3+ and Ce3+–Tb3+ are analysed and determined to be electric dipole–dipole and dipole–quadrupole, respectively. The broad PLE spectra of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs.

Optical properties and energy transfers of Ce3+ and Mn2+ in Ba9Sc2(SiO4)6

Analysis of XRD patterns indicates that Ce3+ and Mn2+ in Ba9Sc2(SiO4)6 (BSS) presents preferably at the Sc3+ and the Ba2+ site, respectively. Ba9Sc2(SiO4)6:Ce3+ (BSS:Ce3+) exhibits an intense emission band peaked at 383nm. Codoping Mn2+ into this material can generate a red emission band at 615nm of Mn2+ through Ce3+–Mn2+ energy transfers (ETs). To achieve the ET mechanisms, critical distance and coefficient, the dynamical processes of the ET are investigated based on Inokuti–Hirayama model. For Ce3+ concentration of 5mol%, the corresponding rate constant and the critical distance are evaluated to be 8.4×10−37cm6s−1 and 0.52nm, respectively. The ET efficiency can reach 48%. The emission intensity ratio of the Mn2+ to the Ce3+ is also studied to understand color-tunable luminescence as the blue Ce3+ is excited by UV light. These results show the promising application of this phosphor for white LEDs.

Tunable luminescence and energy transfer properties of Ca5(PO4)2SiO4:Ce3+/Tb3+/Mn2+ phosphors

A series of single-composition phosphors Ca5(PO4)2SiO4:Ce3+, Tb3+, Mn2+ have been prepared via a high-temperature solid-state reaction process. The Ce3+ emission at different lattice sites has been identified and discussed. The energy transfer from Ce3+ to Tb3+ and Mn2+ ions has been validated. The emissive colors of Ca5(PO4)2SiO4:Ce3+, Tb3+/Mn2+ samples can be adjusted from blue to green and from blue to red-orange by the energy transfer of Ce3+ → Tb3+ and Ce3+ → Mn2+, respectively. More importantly, white emission has been obtained through adjusting the relative concentrations of Ce3+, Tb3+ and Mn2+ ions in the Ca5(PO4)2SiO4 host under UV and low-voltage electron beam excitation, respectively. Additionally, the temperature-dependent photoluminescence and the degradation behaviors of cathodoluminescence under continuous electron bombardment for as-prepared phosphors have been investigated in detail. The results reveal that the Ca5(PO4)2SiO4 host is stable enough to protect the photoluminescence and cathodoluminescence properties of Ce3+, Tb3+ and Mn2+ ions from being affected. Tunable luminescence and the stable structure suggest that Ca5(PO4)2SiO4:Ce3+/Tb3+/Mn2+ phosphors have great potential in the application in WLEDs and FEDs.

Spectroscopic properties and energy transfer of Ce3+/Eu2+ codoped oxide glasses with high Gd2O3 concentration

Eu2+/Ce3+ single doped and co-doped oxide glasses with high Gd2O3 concentration were prepared in a reducing atmosphere using a high-temperature glass melting method. Excitation and emission spectra measurements indicated that Ce3+ can enhance the luminescence intensity of Eu2+ effectively, which exhibited a 2.3 times increasa. The difference between the luminescence lifetimes of Eu2+ with and without Ce3+ doping indicated that the energy transfer efficiency could reach 61.5%, for which the energy transfer mechanism was investigated further. These researches suggest that co-doping method can significantly improve the luminescence capabilities of Eu3+ in the oxide glasses with high Gd2O3 concentration.

Highly bright multicolor tunable ultrasmall β-Na(Y,Gd)F4:Ce,Tb,Eu/β-NaYF4 core/shell nanocrystals

Herein, we report highly bright multicolor-emitting β-Na(Y,Gd)F₄:Ce,Tb,Eu/β-NaYF₄ nanoparticles (NPs) with precise color tunability. First, highly bright sub-20 nm β-Na(Y,Gd)F₄:Ce,Tb,Eu NPs were synthesized via a heating-up method. By controlling the ratio of Eu(3+) to Tb(3+), we generated green, yellow-green, greenish yellow, yellow, orange, reddish orange, and red emissions from the NP solutions via energy transfer of Ce(3+)→ Gd(3+)→ Tb(3+) (green) and Ce(3+)→ Gd(3+)→ Tb(3+)→ Eu(3+) (red) ions under ultraviolet light illumination (254 nm). Because of Ce(3+) and Gd(3+) sensitization, Tb(3+) ions exhibited strong green emission. The decay time of Tb(3+) emission decreased from 4.0 to 1.4 ms as the Eu(3+) concentration was increased, suggesting that energy was transferred from Tb(3+) to Eu(3+). As a result, Eu(3+) emission peaks were generated and the emission color was transformed from green to red. Monodisperse sub-6 nm β-Na(Y,Gd)F₄:Ce,Tb,Eu NPs were synthesized through a simple reduction of the reaction temperature. Although fine color tunability was retained, their brightness was considerably decreased owing to an increase in the surface-to-volume ratio. The formation of a β-NaYF₄ shell on top of the sub-6 nm NP core to produce β-Na(Y,Gd)F₄:Ce,Tb,Eu/β-NaYF₄ significantly increased the emission intensity, while maintaining the sub-10 nm sizes (8.7-9.5 nm). Quantum yields of the ultrasmall NPs increased from 1.1-6.9% for the core NPs to 6.7-44.4% for the core/shell NPs. Moreover, highly transparent core/shell NP-polydimethylsiloxane (PDMS) composites featuring a variety of colors, excellent color tunability, and high brightness were also prepared.

Crystal structure, photoluminescence properties and energy transfer of Ce3+, Mn2+ co-activated Ca8NaGd(PO4)6F2 phosphor

Ca(8−y)MnyNaGd(1−x)Cex(PO4)6F2 (CNGF: xCe3+, yMn2+) (0≤x≤0.05, 0≤y≤0.16) phosphors were synthesized by solid state reaction. The crystal structure was determined to be apatite-type by XRD refinement. The PLE and PL spectra showed that the energy transfer occurs between Gd3+ to Mn2+ and Ce3+ to Mn2+. And the energy transfer efficiency from Gd3+ to Mn2+ and Ce3+ to Mn2+ in CNGF had been analyzed. The research result revealed that the electric dipole–quadrupole interaction predominates in energy transfer mechanism from Ce3+ to Mn2+ in CNGF. The corresponding CIE coordinates revealed that CNGF: 0.02Ce3+, yMn2+ could be a good yellow phosphor.