Recombination processes in the Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> scintillator

The roentgenoluminescence spectra, temperature-dependent activator luminescence, optically stimulated luminescence, and the effect of IR irradiation on the yield and spectral composition of the low-temperature roentgenoluminescence and thermoluminescence curves of the Y₃Al₅O₁₂:Ce³⁺ scintillator have been studied in the temperature range 85–295 K. The results, coupled with earlier data, suggest that the Ce³⁺ ions in the garnet crystal studied form Ce³⁺ p hole centers and increase the concentration of electronic F ^?-centers responsible for the IR stimulation band at 940 nm. The reduction in roentgenoluminescence yield on cooling Y₃Al₅O₁₂:Ce³⁺ to below 230 K is due to the significant localization of excited carriers at defects, which show up in thermoluminescence peaks and optical stimulation spectra. The low-temperature Ce³⁺ luminescence in Y₃Al₅O₁₂:Ce₃₊ seems to result from the recombination of activator-bound excitons.     

Structural and optical characterization of RE (Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) doped SrMg<Subscript>2</Subscript>Al<Subscript>6</Subscript>Si<Subscript>9</Subscript>O<Subscript>30</Subscript> nanocrystalline phosphor

This article present the reports on optical study of Eu²⁺ and Ce³⁺ doped SrMg₂Al₆Si₉O₃₀ phosphors, which has been synthesized by combustion method at 550 °C. Here SrMg₂Al₆Si₉O₃₀:Eu²⁺ emission band observed at 425 nm by keeping the excitation wavelength constant at 342 nm, whereas SrMg₂Al₆Si₉O₃₀:Ce³⁺ ions shows the broad emission band at 383 nm, under 321 nm excitation wavelength, both the emission bands are assigned due to 5d–4f transition respectively. Further, phase purity, morphology and crystallite size are confirmed by XRD, SEM and TEM analysis. However, the TGA analysis is carried out to know the amount of weight lost during the thermal processing. The CIE coordinates of SrMg₂Al₆Si₉O₃₀:Eu²⁺ phosphor is observed at x?=?0.160, y?=?0.102 respectively, which may be used as a blue component for NUV-WLEDs. The critical distance of energy transfer between Ce³⁺ ions and host lattice is found to be 10.65 Å.     

Influence of Mg<Superscript>2+</Superscript>/Ga<Superscript>3+</Superscript> doping on luminescence of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphors

Mg²⁺/Ga³⁺ doped Y₃Al₅O₁₂:Ce³⁺ phosphors were synthesized through a solid state reaction. The phase and luminescent of the synthesized phosphors were investigated. For Ga³⁺ codoped Y_2.96Ce_0.04Al_(5?x)Ga_xO₁₂ phosphors, the emission intensity increases with the increase of Ga³⁺ concentration up to Y_2.96Ce_0.04Al_4.80Ga_0.20O₁₂ and then decreases with a further increase of Ga³⁺ concentration, but the emission peak shifts to shorter wavelength continuously in the Ga³⁺ doping concentration range of 0.05–0.25. For Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors, the emission intensity decreases and the emission peak shifts to longer wavelength continuously in the Mg²⁺ doping concentration range of 0.02–0.12. The emission spectra of Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors demonstrate that the codoped Mg²⁺/Ga³⁺ ions not only induce the enhancement of Y_2.96Ce_0.04Al₅O₁₂ emission intensity but also lead to the red shift of Y_2.96Ce_0.04Al₅O₁₂ emission peak. The decay lifetimes decrease in Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al₅O₁₂ phosphors due to defects formed by substitutions of Y³⁺ by Mg²⁺/Ga³⁺.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Synthesis and luminescence properties of a novel Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> co-doped Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> whiskers by a gel nano-coating method

Al₁₈B₄O₃₃:Eu³⁺, Tb³⁺ whiskers have been successfully prepared by a simple gel nano-coating method using aluminum isopropoxide as the starting materials. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL), and thermogravimetric analysis (TGA) were used characterize the samples. The results show coexistence of the crystal phase Al₁₈B₄O₃₃, amorphous phase, and Eu³⁺, Tb³⁺ ions of the samples with initial addition Al/B ratios from 3 to 1 are incorporated into the amorphous phase. The Al₁₈B₄O₃₃:Eu³⁺, Tb³⁺ whiskers are very straight with an average diameter of 600 nm and lengths ranging from 5 to 10 μm. Under ultraviolet excitation at 365 nm, samples show mainly exhibit the characteristic emission of Eu³⁺ corresponding to \( ^{ 5} {\text{D}}_{ 0} \to {\text{F}}_{ 1 , 2} \) transitions due to an efficient energy transfer occurs from Tb³⁺ to Eu³⁺.     

Synthesis,crystal structure and luminescence in Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript>

Bluish green emitting phosphor, Ca₃Al₂O₆:Ce³⁺, is prepared by low-temperature combustion method. X-ray diffraction, photoluminescence, scanning electron microscopy techniques are used to characterize the synthesized phosphor. The most efficient bluish green (483 nm) emission is observed under the excitation by near UV light. The emission characteristics are credited to 5d → 4f type transitions in Ce³⁺. The luminescence properties of Eu²⁺ are predicted for the first time from those of Ce³⁺. Also, photoluminescence of Eu³⁺ is studied in the same host. The emission spectrum of Ca₃Al₂O₆:Eu³⁺ shows the peak at 592 (orange) and 614 nm (red) wavelengths. Ca₃Al₂O₆:Ce³⁺phosphor can be a potential blue phosphor for field emission display, solid-state lighting and LED.     

Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> luminescence in calcium and strontium aluminates

Compound CaAl₄O₇ (CA4), SrAl₄O₇ (SA4), CaAl₁₂O₁₉ (CA12) and SrAl₁₂O₁₉ (SA12) have been synthesized by using single step combustion method. The phosphors have been characterized by XRD, SEM and PL techniques. Both CA4 and SA4 possess monoclinic crystal structure whereas CA12 and SA12 possess hexagonal structure. Effects of crystal symmetry on the emission spectrum have been studied by doping the samples with Ce³⁺ and Eu²⁺ ions. The luminescence properties of Ce³⁺ and Eu²⁺ in these hosts is discussed on the basis of their covalent character and the crystal field splitting of the d-orbital of dopant ions. The spectroscopic properties, crystal field splitting, centroid shift, red shift and stokes shift have been studied. Spectroscopic properties of Eu²⁺ ions have been accurately predicted from those of Ce³⁺ ions in the same host. Most importantly experimental results were matched excellently with the calculated results. The preferential substitution of Ce³⁺ and Eu²⁺ at different Ca²⁺, Sr²⁺ crystallographic sites have been discussed. The dependence of emission wavelengths of Ce³⁺ and Eu²⁺ on the local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Differences in the emission spectrum of these samples have been observed despite their similar crystal structures and space group. Possible reasons have been discussed.     

Rapid synthesis and enhancement in down conversion emission properties of BaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>,RE<Superscript>3+</Superscript> (RE<Superscript>3+</Superscript>=Y,Pr) nanophosphors

BaAl₂O₄:Eu²⁺,RE³⁺ (RE³⁺=Y, Pr) down conversion nanophosphors were prepared at 600 °C by a rapid gel combustion technique in presence of air using boron as flux and urea as a fuel. A comparative study of the prepared materials was carried out with and without the addition of boric acid. The boric acid was playing the important role of flux and reducer simultaneously. The peaks available in the XPS spectra of BaAl₂O₄:Eu²⁺ at 1126.5 and 1154.8 eV was ascribed to Eu²⁺(3d _5/2) and Eu²⁺(3d _3/2) respectively which confirmed the presence of Eu²⁺ ion in the prepared lattice. Morphology of phosphors was characterized by tunneling electron microscopy. XRD patterns revealed a dominant phase characteristics of hexagonal BaAl₂O₄ compound and the presence of dopants having unrecognizable effects on basic crystal structure of BaAl₂O₄. The addition of boric acid showed a remarkable change in luminescence properties and crystal size of nanophosphors. The emission spectra of phosphors had a broad band with maximum at 490–495 nm due to electron transition from 4f ⁶5d ¹ → 4f ⁷ of Eu²⁺ ion. The codoping of the rare earth (RE³⁺=Y, Pr) ions help in the enhancement of their luminescent properties. The prepared phosphors had brilliant optoelectronic properties that can be properly used for solid state display device applications.     

Combusion synthesis,structural and photo-physical characteristics of Eu<Superscript>2+</Superscript> and Dy<Superscript>3+</Superscript> co-doped SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> phosphor nanopowders

In this research, we reported the synthesis of Eu²⁺ and Dy³⁺ co-doped SrAl₂O₄ phosphor nanopowders with high brightness and long afterglow by urea-nitrate solution combustion synthesis (SCS) at 600 °C, followed by heating the resultant combustion ash at 1,200 °C in a weak reductive atmosphere (5% H₂ + 95% N₂). The broad-band UV-excited luminescence of the SrAl₂O₄: Eu²⁺, Dy³⁺ nanopowders was observed at λ _max = 517 nm due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the emission center (Eu²⁺ ions). The excitation spectra consist of 240- and 254 nm broad peaks. Finally, it was found that the optimum ratio of urea is 2.5 times higher than theoretical quantities for the best emission condition of SrAl₂O₄: Eu²⁺, Dy³⁺ phosphor nanopowders.     

Optical properties of Eu<Superscript>3+</Superscript> activated SrLa<Subscript>2</Subscript>O<Subscript>4</Subscript> red-emitting phosphors for WLED applications

The SrLa_2?xO₄:xEu³⁺ phosphors are synthesized through high-temperature solid-state reaction method at 1473 K with various doping concentration. Their phase structures, absorption spectra, and luminescence properties are investigated by X-ray diffraction (XRD), UV–Vis spectrophotometer and photoluminescence spectrometry. The intense absorption of SrLa_2?xO₄:xEu³⁺ phosphors have occurred around 400 nm. The prominent luminescence spectra of the prepared phosphors exhibited bright red emission at 626 nm. The doping concentration 0.12 mol% of Eu³⁺ is shown to be optimal for prominent red emission and chromaticity coordinates are x?=?0.692, y?=?0.3072. Considering the high colour purity and appropriate emission intensity of Eu³⁺ doped SrLa₂O₄ can be used as red phosphors for white light emitting diodes (WLEDs).     

Luminescence properties and preparation of Lu<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> powder doped with Ce and Pr ions

Lu₃Al₅O₁₂:Ce³⁺ phosphor powder, which exhibits green emission band, was synthesized by the high-temperature solid-state reaction method with a flux BaF₂. X-ray diffraction (XRD), photoluminescence (PL) spectra, and fluorescent lifetime spectra were used to characterize the structure and luminescent properties of the sample. The XRD patterns indicated that when prepared at 1550 °C for 3 h with 4 wt% flux, Lu₃Al₅O₁₂:Ce³⁺ phosphors powder is the garnet cubic crystal system structure. Photoluminescence (PL) spectra showed that the Lu₃Al₅O₁₂:Ce³⁺ phosphor powder can be effectively excited by near ultraviolet and blue light, emitting broad band peaking at 505 nm, which is attributed to ²F_5/2?→?²D_5/2 transition. The self-concentration quenching mechanism of Ce³⁺ is the dipole–dipole interaction. Small amount of Pr³⁺ increased red light emission at 610 nm. Photoluminescence (PL) spectra and fluorescent lifetime spectra indicated that there was an efficient energy transfer process between Ce³⁺ and Pr³⁺.     

Photoluminescence properties of a novel red-emitting phosphor Ba<Subscript>2</Subscript>LaV<Subscript>3</Subscript>O<Subscript>11</Subscript>:Eu<Superscript>3+</Superscript>

Ba₂LaV₃O₁₁:Eu³⁺ phosphors were firstly synthesized by the traditional solid-state reaction method at 1100 °C. Their luminescence properties were investigated by photoluminescence excitation and emission spectra. The excitation spectrum shows a broad band centered at about 275 nm in the region from 200 to 370 nm, which is attributed to an overlap of the charge transfer transitions of O^2??→?V⁵⁺ and O^2??→?Eu³⁺. The phosphors exhibit the red emissions of Eu³⁺ and the emission intensity ratio of ⁵D₀?→?⁷F₂ to ⁵D₀?→?⁷F₁ is dependent on the Eu³⁺ concentration due to an environment change about Eu³⁺ ions. Concentration quenching occurs at 30 mol% in the phosphors and exchange interaction is its main mechanism. Ba₂LaV₃O₁₁:Eu³⁺ displays tunable CIE color coordinates from yellow orange to red depended on Eu³⁺ content, which may have a potential application for illuminating and display devices.     

Synthesis,photoluminescence and mechanoluminescence properties of Eu<Superscript>3+</Superscript> ions activated Ca<Subscript>2</Subscript>Gd<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>14</Subscript> phosphors

A new series of Eu³⁺ ions-activated calcium gadolinium tungstate [Ca₂Gd₂W₃O₁₄] phosphors were synthesized by conventional solid-state reaction method. The X-ray diffraction patterns of the powder samples indicate that the Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors are of tetragonal structure. The prepared phosphors were well characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and mechanoluminescence (ML) spectra. PL spectra of Eu³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ _exci = 392 nm (⁷F₀ → ⁵L₆). The energy transfer from tungstate groups to europium ions has also reported. Mechanoluminescence studies of Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors have also been explained systematically.     

Structure and photoluminescence of ZnGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>

The structure of undoped and europium-doped ZnGa₂Se₄ has been studied, and the interplanar spacings, the Miller indices of the observed reflections, and their relative intensities have been determined. The photoluminescence spectra of ZnGa₂Se₄ and ZnGa₂Se₄:Eu²⁺ crystals have been measured at temperatures from 77 to 230 K. The 566-nm band in the spectrum of ZnGa₂Se₄:Eu²⁺ is assigned to the Eu²⁺4f ⁶5d→4f ⁷(⁸ S _7/2) electronic transition, and the bands at 591 and 646 nm are attributed to transitions of donor-acceptor pairs.     

Electron traps in Gd<Subscript>3</Subscript>Ga<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>12</Subscript>:Ce garnets doped with rare-earth ions

The curves of thermally stimulated luminescence of Gd₃Ga₃Al₂O₁₂:Ce³⁺ ceramics (a nominally pure sample and samples doped with rare-earth ions) are measured in the temperature range of 80–550 K. The depth and the frequency factor of electron traps established by Eu and Yb impurities are determined. An energy-level diagram of rare-earth ions in the bandgap of Gd₃Ga₃Al₂O₁₂ is presented.     

Gamma luminescence of Pr<Superscript>3+</Superscript>- and Ce<Superscript>3+</Superscript>-doped yttrium aluminum garnet crystals

We have studied the gamma luminescence of undoped and Pr³⁺- or Ce³⁺-doped Y₃Al₅O₁₂ crystals gamma-irradiated at 77 and 300 K. The results demonstrate that, depending on temperature, three excitonassisted activator luminescence excitation mechanisms are possible in YAG crystals.     

Recombination luminescence of CaI<Subscript>2</Subscript> crystals activated with Eu<Superscript>2+</Superscript>, Gd<Superscript>2+</Superscript>, Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript>

The spectral characteristics of thermostimulated luminescence, steady-state roentgenoluminescence and photostimulated luminescence (PSL) buildup and decay kinetics, and the effect of IR irradiation on the roentgenoluminescence yield and glow curves of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, CaI₂:Mn²⁺, and CaI₂: Pb²⁺, Mn²⁺ crystals grown by the Bridgman-Stockbarger method have been studied in the temperature range 90–295 K. Coupled with earlier data, the present results on the influence of oxygen and hydrogen impurities on the spectral characteristics of CaI₂ indicate that the activation of calcium iodide with Eu²⁺, Gd²⁺, Tl⁺, Pb²⁺, and Mn²⁺ leads to the formation of cation impurity-native defect complexes, which act as carrier traps and are responsible for the thermostimulated luminescence in the range 150–295 K. IR exposure after 90-K x-ray excitation gives rise to flash PSL and influences the thermostimulated luminescence light sum. The nature of the emission and trapping centers involved and the mechanisms of recombination luminescence excitation in the crystals are discussed.     

Photoluminescence properties and charge compensation investigations of novel orange-emitting Eu<Superscript>3+</Superscript> doped Na<Subscript>4</Subscript>Ca<Subscript>4</Subscript>(Si<Subscript>6</Subscript>O<Subscript>18</Subscript>) phosphors

A series of polycrystalline Na₄Ca₄(Si₆O₁₈):Eu³⁺ orange emitting phosphors were synthesized by a conventional high-temperature solid-state reaction. The phase formation was confirmed by X-ray power diffraction analysis. The excitation spectra show a strong host absorption indicating an efficient energy transfer process from O^2? to Eu³⁺ ions. Upon NUV radiation, the phosphors showed strong red emission around 610 nm (⁵D₀ → ⁷F₂) and orange emission around 591 nm (⁵D₀ → ⁷F₁), but the ⁵D_1,2,3 emission nearly can not be seen. Compared with the luminescence properties of Li⁺, Na⁺, and K⁺ co-doped samples, we deduced that Na⁺ ions probably prefer to dope into the intrinsic Na vacancies rather than Ca²⁺ ions vacancies in Na₄Ca₄(Si₆O₁₈) crystal. Thermal stability properties, quantum efficiency and chromaticity coordinates of the phosphors have been investigated for the potential application in white LEDs.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

The influence of activation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> polycrystalline matrices by Bi<Superscript>3+</Superscript> ions on the luminescence of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

The influence of activation of the Y₂O₃ matrix of the Y₂O₃:Eu³⁺ phosphor by Bi³⁺ ions on the luminescence of Eu³⁺ and Bi³⁺ ions in it and on conditions of the excitation energy transfer to luminescence centers is studied. It is shown that the presence of Bi³⁺ ions leads to the appearance of recombination luminescence with participation of bismuth ions at low concentrations (up to 6–8 at %) of the dominant activator europium and to an increase in the threshold of intrinsic concentration quenching of its luminescence.