PL Properties of Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> With Eu<Superscript>3+</Superscript> and Dy<Superscript>3+</Superscript> for Solid State Lighting Prepared by Precipitation Method

Photoluminescence studies of pure and Dy³⁺, Eu³⁺ doped Sr₂CeO₄ compounds are presented by oxalate precipitation method for solid state lighting. The prepared samples also characterized by XRD, SEM (EDS) and FTIR spectroscopy. The pure Sr₂CeO₄ compound displays a broad band in its emission spectrum when excited with 280 nm wavelength, which peaks centered at 488 nm, which is due to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ions. Emission spectra of Sr₂CeO₄ with different concentration of Dy³⁺ ions under near UV radiation excitation, shows that intensity of luminescence spectra is found to be affected by Dy³⁺ ions, and it increases with adding some percentages of Dy³⁺ ions. The maximum doping concentration for quenching is found to be Dy³⁺?=?0.2 mol % to Sr²⁺ions. The observed broad spectrum from 400 to 560 nm is mainly due to CT transitions in Sr₂CeO₄ matrix and some fractional contribution of transitions between ⁴F_9/2 → ⁶H_15/2 of Dy³⁺ ions. Secondly the effect of Eu³⁺ doping at the Sr²⁺ site in Sr₂CeO₄, have been studied. The results obtained by doping Eu³⁺ concentrations (0.2 mol% to 1.5 mol%), the observed excitation and emission spectra reveal excellent energy transfer between Ce⁴⁺ and Eu³⁺. The phenomena of concentration quenching are explained on the basis of electron phonon coupling and multipolar interaction. This energy transfer generates white light with a color tuning from blue to red, the tuning being dependent on the Eu³⁺ concentration. The results establish that the compound Sr₂CeO₄ with Eu³⁺?=?1 mol% is an efficient “single host lattice” for the generation of white lights under near UV-LED and blue LED irradiation. The commission internationale de I’Eclairage (CIE) coordinates were calculated by Spectrophotometric method using the spectral energy distribution of prepared phosphors.     

Luminescence properties of phosphors based on Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> (TbAG) terbium-aluminum garnet

The processes of excitation energy transfer in phosphors based on single-crystal Tb₃Al₅O₁₂:Ce (TbAG:Ce) and Tb₃Al₅O₁₂:Ce,Eu (TbAG:Ce,Eu) garnet films have been investigated. These films are considered to be promising materials for screens for X-ray images and luminescence converters of blue LED radiation. The conditions for excitation energy transfer from the matrix (Tb³⁺ cations) to Ce³⁺ and Eu³⁺ ions in TbAG:Ce and TbAG:Ce,Eu phosphors have been analyzed in detail. It is established that a cascade process of excitation energy transfer from Tb³⁺ ions to Ce³⁺ and Eu³⁺ ions and from Ce³⁺ ions to Eu³⁺ ions is implemented in TbAG:Ce,Eu via dipole-dipole interaction and through the Tb³⁺ cation sublattice.     

On the Luminescence of Ce<Superscript>3+</Superscript>, Eu<Superscript>3+</Superscript>, and Tb<Superscript>3+</Superscript> in Novel Borate LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>

This paper reports on the photoluminescence (PL) and time-resolved properties of Ce³⁺, Eu³⁺, and Tb³⁺ in novel LiSr₄(BO₃)₃ powder phosphors. Ce³⁺ shows an emission band peaking at 420 nm under 350-nm UV excitation. Energy transfer from Ce³⁺ to Mn²⁺ takes place in the co-doped samples. Eu³⁺ shows red emission under near UV excitation. LiSr₄(BO₃)₃:Eu³⁺ phosphor could be a suitable candidate for phosphor-converted solid state lighting. The luminescence lifetime is 2.13 ms for Eu³⁺ in LiSr₄(BO₃)₃:0.001Eu³⁺. As Eu³⁺ concentration increasing, the decay curves deviate from exponential behavior. Tb³⁺ shows the strongest ⁵D₄→⁷ F₅ emission line at 540 nm. Decay curves of ⁵D₄→⁷ F₅ and ⁵D₃→⁷ F₅ emission with different Tb³⁺ concentrations were also measured. Cross-relaxation process is discussed based on the decay curves.     

Sol-gel method and luminescence properties of the ZrO<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript> phosphors with different charge compensation

Eu³⁺-doped ZrO₂ phosphors with different charge compensators (Li⁺, Na⁺, K⁺) were prepared by the sol-gel method. The properties of the as-obtained samples are characterized by X-ray diffraction, scanning electron microscope, photoluminescence spectra, and decay curve. The results show that ZrO₂:Eu³⁺ phosphors with different charge compensation are mixed phase of tetragonal and monoclinic phase, and the volume fraction of tetragonal phase of ZrO₂:Eu³⁺/Na⁺ phosphor is bigger than the other phosphors. The phosphors can emit strong red light at 606~616 nm (⁵D₀ → ⁷F₂) excited by ultraviolet light (395 nm). Compared with two charge compensation patterns in the ZrO₂:Eu³⁺, it has been found that ZrO₂:Eu³⁺ phosphors used Na⁺ as charge compensator show greatly enhanced red emission under 395 nm excitation and longer luminescence lifetime.     

Luminescence of Eu<Superscript>3+</Superscript> rare-earth ions in Lu<Subscript>2</Subscript>O<Subscript>3</Subscript> nanospheres

The kinetics of luminescence of Eu³⁺ ions in Lu₂O₃:Eu nanospheres with diameters of 100–270 nm and a small standard deviation of the size distribution <15% has been studied. A sharp decrease in the decay time of luminescence of Eu³⁺ ions in the red range with an increase in the diameter of nanospheres has been attributed to the appearance of a photon mode accelerating spontaneous luminescence, which is confirmed by the calculation of ranges of existence of whispering-gallery modes in studied nanospheres.     

Luminescence in Dy<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> Activated K<Subscript>3</Subscript>Al<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The Dy³⁺ and Eu³⁺ activated K₃Al₂ (PO₄)₃ phosphors were prepared by a combustion synthesis. From a powder X-ray diffraction (XRD) analysis the formation of K₃Al₂ (PO₄)₃ was confirmed. In the photoluminescence emission spectra, the K₃Al₂(PO₄)₃:Dy³⁺ phosphor emits two distinctive colors: blue and yellow whereas K₃Al₂(PO₄)₃:Eu³⁺ emits red color. Thus the combination of colors gives BYR (blue–yellow–red) emissions can produce white light. These phosphors exhibit a strong absorption between 340 and 400 nm which suggest that present phosphor is a promising candidate for producing white light-emitting diodes (LED).     

Synthesis and luminescent properties of Eu<Superscript>3+</Superscript>- and Eu<Superscript>2+</Superscript>-activated sodium pyrophosphate Na<Subscript>4</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

The luminescent properties of Eu³⁺ and Eu²⁺ ions in sodium pyrophosphate, Na₄P₂O₇, have been studied. The excitation spectrum of the Eu³⁺ emission in Na₄P₂O₇ consists of several sets of bands in the range 280–535 nm due to 4f–4f transitions of Eu³⁺ ions and a broad band with a maximum at about 240 nm interpreted to be due to a charge transfer (CT) transition from oxygen 2p states to empty states of the Eu³⁺ 4f⁶-configuration. Although the CT band energy is large enough, the quantum efficiency (η) of the Eu³⁺ emission in Na₄P₂O₇ under CT excitation was estimated to be very low (η ≤ 0.01). In terms of a configurational coordinate model, this fact is interpreted as a result of the high efficiency of a radiationless relaxation from the CT state to the ⁷F₀ ground state of Eu³⁺ ions occupying sodium sites in Na₄P₂O₇. A strong reducing agent is required in order to stabilize Eu²⁺ ions in Na₄P₂O₇ during the synthesis. Several nonequivalent Eu²⁺ luminescence centers in Na₄P₂O₇ were found.     

Efficient VUV sensitization of Eu3+ emission by Tb3+ in potassium rare‐earth double phosphate

The luminescence properties of K₃Tb(PO₄)₂ activated by Eu³⁺ were studied at excitation over the 120–300 nm wavelength range. It is demonstrated that Tb³⁺ ions, exhibiting a strong absorption band in the vacuum‐ultraviolet (VUV), can provide efficient sensitisation of Eu³⁺ emission in this wave length range, giving rise to intense red luminescence at 150 nm excitation. A proof is given for the concept of VUV sensitisation enabling the engineering of luminescence materials with enhanced conversion efficiency of VUV radiation into visible light. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Silica gel glasses with a high efficiency of luminescence sensitization in the Ce<Superscript>3+</Superscript>-Tb<Superscript>3+</Superscript> system

Terbium-and (Ce, Tb)-containing glasses prepared using the direct sol-gel-glass transition are studied. It is shown that glasses doped with one activator contain two main types of optical centers, namely, isolated and complex centers, which are characterized by weak and strong cross-relaxation quenching of luminescence from the ⁵D₃ state of Tb³⁺ ions, respectively. The Ce⁴⁺-Tb³⁺ (Tb⁴⁺) complex centers are formed during sintering of coactivated xerogels in oxygen and can be transformed into Ce³⁺-Tb³⁺ centers through saturation of the samples with hydrogen. The Ce³⁺-Tb³⁺ centers exhibit efficient luminescence from the ⁵D₄ state upon excitation into the absorption bands of Ce³⁺ ions.     

Red,Yellow, Blue and Green Emission from Eu<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript> and Bi<Superscript>3+</Superscript> Doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>nano-Phosphors

Rare earth elements (RE = Eu³⁺& Dy³⁺)and Bi³⁺ doped Y₂O₃ nanoparticles were synthesized by urea hydrolysis method in ethylene glycol, which acts as reaction medium as well as a capping agent, at a low temperature of 140 °C,followed by calcination of the obtained product. Transmission electron microscope (TEM) images reveals that ovoid shaped Y₂O₃ nanoparticles of around 22–24 nm size range were obtained in this method. The respective RE and Bi³⁺ doped Y₂O₃ precursor nanoparticles when heated at 600 and 750 °C, retains the same shape as that of the as-synthesized Y₂O₃ precursor samples. From EDAX spectra, the incorporation of RE ions into the host has been studied. XRD pattern reveals the crystalline nature of the heated nanoparticles and indicate the absence of any impurity phase other than cubic Y₂O₃.However, the as-synthesized nanoparticles were highly amorphous without the presence of any sharp XRD peaks. Photoluminescence study suggests that the synthesized samples could be used as red (Eu³⁺), yellow (Dy³⁺), blue and green (Bi³⁺)emitting phosphors.     

Synthesis and Optical Properties of Novel Red-Emitting PbNb<Subscript>2</Subscript>O<Subscript>6</Subscript>: Eu<Superscript>3+</Superscript> Phosphors

Undoped and PbNb₂O_6:Eu³⁺ (1.0 ≤ x ≤ 6.0 mol%) phosphors were synthesized at 1100 °C for 3.5 h by the conventional solid state reaction method. Synthesized PbNb₂O₆:Eu³⁺ phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed series of excitation peaks between 350 and 430 nm due to the 4f–4f transitions of Eu³⁺. For 395.0 nm excitation, emission spectra of Eu³⁺ doped samples were observed at 591 nm (orange) and 614 nm (red) due to the ⁵D₀ → ⁷F₁ transitions and ⁵D₀ → ⁷F₂ transitions, respectively. PL analysis results also showed that the emission intensity increased by increasing Eu³⁺ ion content. No concentration quenching effect was observed. The CIE chromaticity color coordinates (x,y) of the PbNb₂O₆:Eu³⁺ phosphors were found to be in the red region of the chromaticity diagram.     

Synthesis and luminescence properties of the red phosphor CaZrO<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> for white light-emitting diode application

Eu³⁺-doped CaZrO₃ phosphor with perovskite-type structure was synthesized by the high temperature solid-state method. The samples were characterized by X-ray diffraction, scanning electron microscopy, fluorescence spectrophotometer and UV-vis spectrophotometer, respectively. XRD analysis showed that the formation of CaZrO₃ was at the calcinations temperature of 1400°C. The average diameter of CaZrO₃ with 4 mol% doped-Eu³⁺ was 2μm. The PL spectra demonstrated that CaZrO₃:Eu³⁺ phosphor could be excited effectively in the near ultraviolet light region (397 nm) and emitted strong red-emission lines at 616 nm corresponding to the forced electric dipole ⁵ D ₀ → ⁷ F ₂ transitions of Eu³⁺. Meanwhile, the light-emitting diode was fabricated with the Ca_0.96ZrO³:Eu_0.04³⁺ phosphor, which can efficiently absorb ∼ 400 nm irradiation and emit red light. Therefore Ca_0.96ZrO₃:Eu_0.04³⁺ may have applications for a near ultraviolet InGaN chip-based white light-emitting diode.     

Cytotoxicity and inflammation in human alveolar epithelial cells following exposure to occupational levels of gold and silver nanoparticles

This study explores the viability of rare earth-doped zirconia nanophosphors as probable candidates for white light emission. Undoped ZrO₂ and single- and double-doped ZrO₂:M (where M?=?Tb³⁺ and Eu³⁺) nanophosphors have been synthesized using a simple sonochemical process. The products were characterized using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), and photoluminescence spectrophotometry. The SEM micrographs show that resultant nanoparticles have dendritic shape. TEM and HRTEM studies showed that the size of the majority of the nanoparticles were around 28?±?5?nm. Characteristic blue and green emission from Tb³⁺ ions and red from Eu³⁺ dopant ions were observed. The CIE coordinates of the double-doped ZrO₂:Tb³⁺ (1.2?%):Eu³⁺ (0.8?%) nanophosphor lie in the white light region of the chromaticity diagram and show promise as good phosphor materials for new lighting devices.     

luminescence of BaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript> crystals activated by Eu<Superscript>2+</Superscript> and Ce<Superscript>3+</Superscript> ions

We have studied the effect of doping with Eu²⁺ and Ce³⁺ ions on the photoluminescence (PL) of BaGa₂Se₄ crystals in the temperature range 77–300 K. We have established that the broad bands with maxima at wavelengths 456 nm and 506 nm observed in the photoluminescence spectra of BaGa₂Se₄:Ce³⁺ crystals are due to intracenter transitions 5d → ²F_7/2 and 5d →²F_5/2 of the Ce³⁺ ions, while the broad photoluminescence band with maximum at 521 nm in the spectrum of BaGa₂Se₄:Eu²⁺ is associated with 4f⁶ 5d → 4f⁷ (⁸S_7/2) transitions of the Eu²⁺ ion. We show that in BaGa₂Se₄:Eu²⁺,Ce³⁺ crystals, excitation energy is transferred from the Ce³⁺ ions to the Eu²⁺ ions.     

Tailoring red-green-blue emission from Er3+, Eu3+ and Tb3+ doped Y2O3 nanocrystals produced via PVA-assisted sol-gel route

Y₂O₃ luminescent nanoparticles were synthesized via PVA-assisted sol-gel method and their structural and optical properties were investigated. Effects of rare earth (Er³⁺, Eu³⁺ and Tb³⁺) doping on luminescence properties of the produced nanophosphors have been investigated under NIR (800 nm) and UV (240–300 nm) excitation. Intense infrared to red and green emissions were observed and a weak blue upconverted luminescence was also detected. Moreover, it was observed that changing the doping ions, the color emitted by the samples could be modified and different combinations of UV excitation and doping produced effective white light emissions. The obtained results demonstrate that PVA-assisted sol-gel is an effective methodology for the synthesis of rare-earth doped Y₂O₃ nanophosphors.     

Luminescence characteristics of energy transfer between Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> in NaMgPO<Subscript>4</Subscript> phosphor

Powder samples of NaMgPO₄ doped with Eu²⁺ and Ce³⁺ were prepared and their photoluminescence spectra were systemically studied. Energy transfer from Ce³⁺ to Eu²⁺ in NaMgPO₄ phosphor was observed by investigating the optical properties from photoluminescence spectra in Eu²⁺ or Ce³⁺ singly doped and Eu²⁺–Ce³⁺ codoped sodium magnesium orthophosphates, NaMgPO₄. The enhancement of UV excitation is attributed to energy transfer from Ce³⁺ to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺–Eu²⁺ codoped NaMgPO₄ phosphors in which Eu²⁺ can be efficiently excited by 390 nm are potential candidates for phosphor-converted LEDs.     

Luminescent properties of (Y,Gd)BO3:Bi,RE (RE=Eu, Tb) phosphor under VUV/UV excitation

Bi³⁺- and RE³⁺-co-doped (Y,Gd)BO₃ phosphors were prepared and their luminescent properties under vacuum ultraviolet (VUV)/UV excitation were investigated. Strong red emission for (Y,Gd)BO₃:Bi³⁺,Eu³⁺ and strong green emission for (Y,Gd)BO₃:Bi³⁺,Tb³⁺ are observed under VUV excitation from 147 to 200 nm with a much broader excitation region than that of single Eu³⁺-doped or Tb³⁺-doped (Y,Gd)BO₃ phosphor. Strong emissions are also observed under UV excitation around 265 nm where as nearly no luminescence is observed for single Eu³⁺-doped or Tb³⁺-doped (Y,Gd)BO₃. The luminescence enhancement of Bi³⁺- and RE³⁺-co-doped (Y,Gd)BO₃ phosphors is due to energy transfer from Bi³⁺ ion to Eu³⁺ or Tb³⁺ ion not only in the VUV region but also in the UV region. Besides, host sensitization competition between Bi³⁺ and Eu³⁺ or Tb³⁺ is also observed. The investigated phosphors may be preferable for devices with a VUV light 147-200 nm as an excitation source such as PDP or mercury-free fluorescent lamp.     

Luminescent properties of SrMg<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript> as a potential phosphor for ultraviolet light-emitting diodes

Eu²⁺ and Mn²⁺ co-doped SrMg₂(PO₄)₂ phosphors with blue and red two emission bands were prepared by the high temperature solid state method and their luminescent properties have been investigated as a function of activator and co-activator concentrations. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the Eu²⁺ emission spectrum and the excitation spectrum of Mn²⁺. Efficiencies of energy transfer were also calculated according to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission. According to the principle of energy transfer, we demonstrated that the phosphor SrMg₂(PO₄)₂:Eu²⁺,Mn²⁺ with double emission bands exhibited a great potential as a phosphor for ultraviolet light-emitting diodes and the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺. PACS 78.55.-m     

Feasibility Study of VUV Sensitization Effect of Tb3+

The possibility to use Tb³⁺ as luminescence sensitizer for enhancement of the conversion efficiency of vacuum-ultraviolet (VUV) radiation into visible light was examined. We studied the luminescence properties of K₃Tb(PO₄)₂ and Ba₃Tb(PO₄)₃ activated by Eu³⁺, and of SrAl₁₂O₁₉ co-doped with Mn²⁺ and Tb³⁺ at excitation over the 120 to 300 nm wavelength range. It is shown that Tb³⁺ ions, exhibiting a strong absorption band in the VUV, can provide efficient sensitization of Eu³⁺ and Mn²⁺ emissions for excitation in this spectral range, giving rise to intense red and green luminescence, respectively. This study provides a proof for the concept of VUV sensitization, which enables the engineering of luminescence materials with improved efficiency for excitation from a noble gas discharge.     

Concentration quenching anomalies of activated Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Pr<Superscript>3+</Superscript> nanocrystal luminescence

For the fist time in Y₂SiO₅:Pr³⁺ nanocrystals, the ordered stage in the ¹ D ₂ luminescence decay curves for Pr³⁺ ions has been observed at anomalously low doped ion concentration (0.5 at %). This effect is caused by preferred location of the activator ions in the near-surface layer of the nanocrystal that provides the relaxation of elastic tension arising due to the difference of ionic radii of Pr³⁺ and Y³⁺ ions. Concentration quenching of Pr³⁺ luminescence is caused by the cooperative cross-relaxation.