5d→4f transition in halosulphate phosphors

The synthesis, X-ray diffraction and photoluminescence characteristics in alkaline halosulphate phosphors, such as KZnSO₄Cl:Ce; KMgSO₄Cl:Ce; NaMgSO₄F:Ce and Na₃SO₄F:Ce is reported in this paper. The Ce³⁺ emission in KMgSO₄Cl:Ce phosphor is maximum and it may be useful for scintillation applications.     

Dyand Mn emission in KMgSO4Cl phosphor

In the present paper, KMgSO₄Cl:Ce³⁺, KMgSO₄Cl:Ce³⁺,Dy³⁺, and KMgSO₄Cl:Ce³⁺,Mn²⁺, new halosulphate phosphors were synthesized by wet chemical method. X-ray powder diffraction (XRD) and photoluminescence (PL) characterization of phosphors have been reported in this paper. The effects of Dy³⁺ co-doping on the PL characteristics of KMgSO₄Cl:Ce phosphor were studied. Energy transfer from Ce³⁺→Dy³⁺and Ce³⁺→Mn²⁺ results in increase in PL peak intensity suggesting that Ce³⁺ plays an important role in PL emission in the present matrix. The PL emission spectra have two peaks (482 and 571 nm) and a single peak (564 nm), which could be attributed to the Ce³⁺→Dy³⁺and Ce³⁺→Mn²⁺ emissions, respectively.     

Low temperature quenching and high efficiency Tm, La or Tb co-doped CaSc2O4:Ce phosphors for light-emitting diodes

Low temperature quenching and high efficiency CaSc₂O₄:Ce³⁺ (CSO:Ce³⁺) phosphors co-doped with Tm³⁺, La³⁺ and Tb³⁺ ions were prepared by a solid state method and the phase-forming, morphology, luminescence and application properties of these phosphors were investigated. The results showed that co-doping of Tm³⁺, La³⁺ and Tb³⁺ ions can improve the luminescence properties and decrease temperature quenching of CSO:Ce³⁺ phosphor remarkably. High efficiency green-light-emitting diodes were fabricated with the prepared phosphors and InGaN blue-emitting (∼460 nm) chips. The good performances of the green-light-emitting LEDs made from co-doped CSO:Ce³⁺ phosphors confirm the luminescence enhancement and indicate that Tm³⁺, La³⁺ and Tb³⁺ co-doped CSO:Ce³⁺ phosphors are suitable candidates for the fabrication of high efficiency white LEDs.     

Photoluminescence spectra of thenardite Na2SO4 activated with rare-earth ions, Ce, Sm, Tb, Dy and Tm

Five Na₂SO₄:RE³⁺ phosphors activated with rare-earth (RE) ions (RE³⁺=Ce³⁺, Sm³⁺, Tb³⁺, Dy³⁺ and Tm³⁺) were synthesized by heating natural thenardite Na₂SO₄ from Ai-Ding Salt Lake, Xinjiang, China with small amounts of rare-earth fluorides, CeF₃, SmF₃, TbF₃, DyF₃ and TmF₃, at 920 °C in air. The photoluminescence (PL) and optical excitation spectra of the obtained phosphors were measured at 300 and 10 K. In the PL spectrum of Na₂SO₄:Ce³⁺ at 300 K, two overlapping bands with peaks at 335 and 356 nm due to Ce³⁺ were first observed. Narrow bands observed in PL and excitation spectra of Na₂SO₄:RE³⁺ (RE³⁺=Sm³⁺, Tb³⁺, Dy³⁺ and Tm³⁺) phosphors were well identified with the electronic transitions within the 4fⁿ (n=5, 8, 9 and 12) configurations of RE³⁺. The existence of excitation bands with high luminescence efficiency at wavelengths shorter than 230 nm is characteristic of Na₂SO₄:RE³⁺ (RE³⁺=Sm³⁺, Tb³⁺, Dy³⁺ and Tm³⁺) phosphors. The obtained results suggest that these phosphors are unfavorable as the phosphor for usual fluorescence tubes, i.e., mercury discharge tubes, but may be favorable as the phosphor for UV-LED fluorescent tubes and as cathodoluminescence, X-ray luminescence and thermoluminescence phosphors.     

Luminescence of KCaSO4Cl:X, Y (X=Eu or Ce; Y=Dy or Mn) halosulfate material

Polycrystalline KCaSO₄Cl:Eu, Dy, KCaSO₄Cl:Ce, Dy and KCaSO₄Cl:Ce, Mn phosphors prepared by a solid state diffusion method have been studied for its photoluminescence (PL) characteristics. The presence of two overlapping bands at around 400 and 450 nm in the PL emission spectra of the phosphor suggests the presence of Eu²⁺ in the host compound occupying two different lattice sites. The effects of co-doping on the photoluminescence (PL) characteristics of KCaSO₄Cl:Eu or Ce phosphors have been studied. The decrease in peak intensity of the phosphor on co-doping it with Dy gives an insight into the emission mechanism of the phosphors, which involves energy transfer from Eu²⁺→Dy³⁺, Ce³⁺→Dy³⁺ and Ce³⁺→Mn²⁺.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

Low thermal quenching and high-efficiency Ce, Tb-co-doped Ca3Sc2Si3O12 green phosphor for white light-emitting diodes

Low thermal quenching and high-efficiency Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSSO:Ce³⁺) phosphors with co-doping Tb³⁺ ion were prepared by a solid state method and the properties of these phosphors were investigated. The results showed that co-doping of Tb³⁺ not only enhances the photoluminescence remarkably and decreases the thermal quenching of the phosphor, but also heightens the performances of the LEDs fabricated with the phosphor. A high-efficiency and low color temperature white LED was fabricated with the prepared CSSO:1%Ce³⁺, 0.5%Tb³⁺ and a red phosphor, indicating that CSSO:1%Ce³⁺,0.5%Tb³⁺ phosphor is a suitable green phosphor for the fabrication of high-efficiency white LEDs.     

Energy transfer and luminescent properties of Ce, Cr co-doped Y3Al5O12

The phosphors in the system Y_3−xAl_5-yO₁₂:xCe³⁺,yCr³⁺ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have absorption in the visible light region and give luminescence in the far-red region (∼688 nm), which are suitable for the application in the device of luminescent solar concentrator (LSC). In these phosphors, Ce³⁺ located at Y³⁺ site can effectively transfer its absorbed energy to Cr³⁺ at Al³⁺ site.     

Photoluminescence characterization of Ce and Dy doped Li2CaGeO4 phosphors

Ce³⁺ and Dy³⁺ activated Li₂CaGeO₄ phosphors were prepared by a solid-state reaction method, and characterized by XRD (X-ray diffraction) and photoluminescence techniques. The characteristic emission bands of Dy³⁺ due to ⁴F_9/2→⁶H_15/2 (blue) and ⁴F_9/2→⁶H_13/2 (yellow) transitions were detected in the emission spectra of Li₂CaGeO₄:Dy³⁺. Ce³⁺ broad band emission was observed in Li₂CaGeO₄:Ce³⁺ phosphors at 372 and 400 nm due to 5d→4f transition when excited at 353 nm. Co-doping of Ce³⁺ enhanced the luminescence of Dy³⁺ significantly and concentration quenching occurs when Dy³⁺ is beyond 0.04 mol%. White-light with different hues can be realized by tuning Dy³⁺ concentration in the phosphors.     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.     

Ca₂BO₃Cl:Ce³⁺,Tb³⁺:A novel tunable emitting phosphor for white light-emitting diode

<正>Ca₂BO₃Cl:Ce³⁺,Ca₂BO₃Cl:Tb³⁺,and Ca₂BO₃Cl:Ce³⁺,Tb³⁺ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl is influenced by the Ce³⁺ or Tb³⁺ doping content,and the optimum concentrations of Ce³⁺ and Tb³⁺ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce³⁺ or Tb³⁺.The Ca₂BO₃Cl:Ce³⁺,Tb³⁺ can produce colour emission from blue to green by properly tuning the relative ratio between Ce³⁺ and Tb³⁺,and the emission intensity of Tb³⁺ in Ca₂BO₃Cl can be enhanced by the energy transfer from Ce³⁺ to Tb³⁺.The results indicate that Ca₂BO₃Cl:Ce³⁺,Tb³⁺ may be a promising double emission phosphor for UV-based white light emitting diodes.     

Luminescence properties and energy transfer in Ba2Y(BO3)2Cl:Ce3+,Tb3+ phosphors

Novel green-emitting Ba₂Y(BO₃)₂Cl:Ce³⁺,Tb³⁺ phosphors were synthesized by a solid-state method. X-ray diffraction and photoluminescence spectra were utilized to characterize the structures and luminescence properties of the as-synthesized phosphors, respectively. Ba₂Y(BO₃)₂Cl:Ce³⁺,Tb³⁺ phosphors exhibit blue and green emission bands under the excitation of near-ultraviolet light. An asymmetric blue emission originates from the Ce³⁺ ion, whereas the green emission originates from the Tb³⁺ ion. A spectral overlap is found between the emission band of the Ce³⁺ ion and the excitation band of the Tb³⁺ ion, which supports the occurrence of the energy transfer from the Ce³⁺ ion to the Tb³⁺ ion. Meanwhile, the energy transfer is thoroughly investigated by their photoluminescence decay behaviors. The energy-transfer efficiency from the Ce³⁺ ion to the Tb³⁺ ion is also calculated, and a possible mechanism is proposed.     

Photoluminescence of SrGa2S4:Sn,Re(=Ce, Gd) phosphors

The photoluminescence (PL) spectra, PL excitation spectra, color coordinates, and X-ray diffraction spectra are reported for SrGa₂S₄:Sn,Re(=Ce and Gd, respectively) phosphors. By mixing SrGa₂S₄:Sn,Ce phosphors with different Ce³⁺ concentrations, white emissions can be obtained under the excitation of a 340-nm UV LED. Emissions in the green to yellow color range can be obtained from SrGa₂S₄:Sn,Gd phosphors. The rare earth ions enhance the green emission band, which peaks at 534 nm, instead of the yellow one. The origin of this enhancement is discussed. The resonant energy transfer rates are estimated in the cases from Ce³⁺ to the green and yellow centers of Sn²⁺ and between the yellow centers and the green centers.     

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y₃Al₅O₁₂: Ce³⁺/Tb³⁺ (average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the sol-gel method, resulting in the formation of core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ shells on the SiO₂ cores (average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1–3 kV), the core-shell SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles show strong yellow-green and green emission corresponding to the 5d–4f emission of Ce³⁺ and ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission of Tb³⁺, respectively. These phosphors may have potential application in field emission displays.     

Ca2BO3Cl:Ce,Eu: A potential tunable yellow-white-blue-emitting phosphors for white light-emitting diodes

Polycrystalline Ca₂BO₃Cl:Ce³⁺,Eu²⁺ phosphors were synthesized by a solid-state reaction and which could display tunable color emission from blue to yellow under an ultraviolet (UV) source by adjusting the ratio of Ce³⁺ and Eu²⁺ appropriately. The mechanism of resonance-type energy transfer from Ce³⁺ to Eu²⁺ was established to be electric dipole-dipole natured, and the critical distance was estimated to be 31 Å based on the spectral overlap and concentration quenching model. A white light was obtained from Ca₂BO₃Cl:0.06Ce³⁺,0.01Eu²⁺ phosphor with chromaticity coordinates (x=0.31, y=0.29) and relative color temperature of 7330 K upon excitation with 360 nm, which is potentially a good candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

Enhanced luminescence of Tb by efficient energy transfer from Ce in Sr2B5O9Cl host

Ce³⁺ and Tb³⁺ co-doped Sr₂B₅O₉Cl phosphors with intense green emission were prepared by the conventional high-temperature solid-state reaction technique. A broad band centered at about 315 nm was found in phosphor Sr₂B₅O₉Cl: Ce³⁺, Tb³⁺ excitation spectrum, which was attributed to the 4f-5d transition of Ce³⁺. The typical sharp line emissions ranging from 450 to 650 nm were originated from the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. The photoluminescence (PL) intensity of green emission from Tb³⁺ was enhanced remarkably by co-doping Ce³⁺ in the Tb³⁺ solely doped Sr₂B₅O₉Cl phosphor because of the dipole-dipole mechanism resonant energy transfer from Ce³⁺ to Tb³⁺ ions. The energy transfer process was investigated in detail. In light of the energy transfer principles, the optimal composition of phosphor with the maximum green light output was established to be Sr_1.64Ce_0.08Tb_0.1Li_0.18B₅O₉Cl by the appropriate adjustment of dopant concentrations. The PL intensity of Tb³⁺ in the phosphor was enhanced about 40 times than that of the Tb³⁺ single doped phosphor under the excitation of their optimal excitation wavelengths.     

Luminescent characteristics of LiCaBo3:M (M=Eu, Sm, Tb, Ce, Dy) phosphor for white LED

LiCaBO₃:M (M=Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors were synthesized by a normal solid-state reaction using CaCO₃, H₃BO₃, Li₂CO₃, Na₂CO₃, K₂CO₃, Eu₂O₃, Sm₂O₃, Tb₄O₇, CeO₂ and Dy₂O₃ as starting materials. The emission and excitation spectra were measured by a SHIMADZU RF-540 UV spectrophotometer. And the results show that these phosphors can be excited effectively by near-ultraviolet light-emitting diodes (UVLED), and emit red, green and blue light. Consequently, these phosphors are promising phosphors for white light-emitting diodes (LEDs). Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Photoluminescence properties and synthesis of nano-sized YAG: Ce phosphor via novel synthesis method

This study reports an approach for enhancing the luminescent properties of Y₃Al₅O₁₂: Ce³⁺_0.07 using an organic compound precursor. The Y₃Al₅O₁₂: Ce³⁺_0.07 nano-sized phosphors had a relatively uniform particle size, approximately 50-80 nm, when sintered at 1200 °C for 1 h. The photoluminescence results showed the maximum peak intensity when the concentration of Ce³⁺ ions was 0.07 mol. The results suggest that nano-sized phosphors synthesized from organic compound precursors can be used as alternative efficiency emitting phosphors in the LED applications.     

Near infrared fluorescence and energy transfer in Ce/Nd Co-doped CaxSr1−xS

Novel near infrared (NIR) phosphors Ca_xSr_1−xS:Ce³⁺,Nd³⁺ were synthesized by a solid state reaction. The NIR emission was realized through an efficient absorption by the allowed 4f-5d transition of Ce³⁺ and efficient energy transfer to Nd³⁺ via well-matched energy levels. Ce³⁺ and Nd³⁺ content in CaS/SrS was optimized. It was found that CaS:Ce³⁺,Nd³⁺ gave much stronger NIR emission than that of SrS:Ce³⁺,Nd³⁺. Further studies on Ca_xSr_1−xS:Ce³⁺,Nd³⁺ indicated that both visible emission of Ce³⁺ and NIR emission of Nd³⁺ were observably affected by Ca/Sr ratio. The energy transfer efficiency, which can be estimated from fluorescence lifetime of Ce³⁺, increased from 52% to 74% for the Ca_xSr_1−xS:Ce³⁺,Nd³⁺ (x=0 to 1) series, accompanied with a shift of maximal emission wavelength of Ce³⁺ from 482 to 505 nm. The results showed that overlap between emission spectrum of Ce³⁺ and excitation spectrum of Nd³⁺ plays an important role in the energy transfer efficiency, and Ce³⁺ emitting in green or blue-greenish region sensitized the Nd³⁺ NIR fluorescence emission more efficiently than that in blue region.     

Luminescent properties of KGd1−x(WO4)2:Eux and KGd1−x(WO4)2−y(MoO4)y:Eux phosphors in UV-VUV regions

KGd_1−x(WO₄)_2−y(MoO₄)_y:Eu³⁺_x(0.1?x?0.75, y=0 and 0.2) phosphors are synthesized through traditional solid-state reaction and their luminescent properties in ultraviolet (UV) and vacuum ultraviolet (VUV) regions are investigated. Under 147 nm excitation, these phosphors show characteristic red emission with good color purity. In order to improve their emission intensity, the MoO₄²⁻ (20 wt%) is introduced into the anion of KGd_1−x(WO₄):Eu³⁺_x. The Mo⁶⁺ and Eu³⁺ co-doped KGd(WO₄)₂ phosphors show higher emission intensity in comparison with the singly Eu³⁺-doped KGd(WO₄)₂ in VUV region. The chromaticity coordination of KGd_0.45(WO₄):Eu³⁺_0.55 is (x=0.669, y=0.331), while that of KGd_0.45(WO₄)_1.8(MoO₄)_0.2:Eu³⁺_0.55 is (x=0.666, y=0.334) in VUV region.