Absorption and luminescence spectra of Pr3+ in CaWO4 monocrystals

A complete diagram of the Stark sublevels of Pr³⁺ for the P_0,1;¹D₂;³F_2,3 terms has been constructed on the basis of a study of the absorption and luminescence spectra of CaWO₄ crystals containing Pr³⁺. Strong splitting of the Pr³⁺ terms in the environment examined has been established.The authors would like to thank Assistant Professor L. Ya. Shekun for suggesting the subject of this work and for his constant interest.     

Resonant processes causing photon multiplication in CaSO4:Tb3+

The emission spectra of single and polyterbium centers have been measured at the excitation of CaSO₄:Tb³⁺ phosphors with different charge compensators (Na⁺, calcium vacancies, etc.) by 3.8–35 eV photons or 5 and 300 keV electrons at 6–300 K. The possible mechanisms providing quantum yield above unity for green (⁵D₄ → ⁷F_J) and blue emission (⁵D₃ → ⁷F_J) of Tb³⁺ at the direct intracenter excitation, excitation of oxyanions or creation of hot (nonrelaxed) electrons and holes have been discussed. On the basis of thermally stimulated luminescence at 6–600 K, the peculiarities of the hopping diffusion of relaxed electrons and holes and their tentative low-temperature self-trapping have been considered.     

Synthesis and characterization of fast-decaying bluish green phosphors of Tb3+-doped CaSi2O2N2 for 2D/3D plasma display panels

Oxynitride phosphor powders comprising of CaSi₂O₂N₂ doped with Tb³⁺ were successfully synthesized using a high-temperature solid-state reaction method. The experimentally determined photoluminescence (PL) properties of the produced phosphors meet the requirements of 2D/3D plasma display panels (PDPs). In particular, under the excitation of vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation, emission peaks corresponding to the ⁵D₃→⁷F_J (J=6, 5, 4, 3) and ⁵D₄→⁷F_J (J=6, 5, 4, 3) transitions of Tb³⁺ ions were recorded. Monitoring the ⁵D₄→⁷F₅ emission of Tb³⁺ at 545 nm, the excitation bands were assigned to the host-related absorption as well as the 4f–5d (fd) and the 4f–4f (ff) transitions of Tb³⁺. The produced phosphors can be efficiently excited at 147 nm, and have an adequately short decay time (τ_1/10=1.14 ms).     

Luminescence and red long afterglow investigation of Eu3+–Sm3+ CO-doped CaWO4 phosphor

A series of Eu³⁺–Sm³⁺ co-doped CaWO₄ phosphors were synthesized by the high temperature solid-state method. The crystal structure of the obtained samples was identified by XRD, and the results showed that all the phases were indexed to scheelite structure. The effect of the doping concentration of Sm³⁺ on the luminescent properties of the obtained products was investigated, and the optimal Sm³⁺ concentration was experimentally determined to 0.5%. The photoluminescence properties indicate that there is an efficient energy transfers from Sm³⁺ to Eu³⁺. The energy-transfer process between Sm³⁺ and Eu³⁺ was also given. Red long afterglow originating from the ⁵D₀–⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ was observed after samples were excited by 254 nm, and the duration of the optimal sample can last more than 35 min in dark with naked eyes. The proposed explanation for the afterglow property was also discussed.     

Low-temperature investigation of electronic excitations in wide-gap materials doped with RE3+ or Cr3+ ions

The processes of photon multiplication in insulators have been considered. The luminescence of Tb³⁺ ions (⁵ D ₃ → ⁷ F _J , ⁵ D ₄ → ⁷ F _J transitions) upon intracenter excitation, the optical excitation of oxyanions, or the formation of separated electrons and holes has been studied for CaSO₄ doped with Tb³⁺ and Na⁺ ions at 6–9 K. An increase in Tb³⁺ concentration from 0.2 to 4 at % and transition from single Tb³⁺-Na⁺ states to centers that contain two or three terbium ions leads to the redistribution of the luminescence intensities in favor of the ⁵ D ₄ → ⁷ F _J transitions and increase in their efficiency due to the possibility of the cooperative ⁵ D ₃ → ⁵ D ₄ and ⁷ F ₆ → ⁷ F _J transitions and the 4f ⁷5d ¹ → ⁵ D ₃ and ⁷ F ₆ → ⁵ D ₄ transitions in the two- and three-terbium centers. Based on the example of MgO single crystals with highly mobile excitons, holes, and electrons, the migration of free excitons and holes toward Cr³⁺ ions in the crystal bulk and their exit from the bulk to the surface have been revealed at 9 K. Surface losses limit the luminescence quantum yield of MgO:Cr³⁺, CaSO₄:Tb³⁺, and many other materials.     

Luminescence of Ca(NbO3)2:Pr at ambient and high hydrostatic pressure

In this contribution, photoluminescence and time-resolved photoluminescence spectra of Ca(NbO₃)₂ doped with Pr³⁺ obtained at high hydrostatic pressure up to 72 kbar applied in a diamond anvil cell are presented. At ambient conditions, the emission spectrum obtained in the time interval 0-1 μs is dominated by spin-allowed transitions from the ³P₀ state. On the other hand, transitions from ¹D₂, characterized by a decay time equal to 30 μs dominate the steady-state luminescence.At pressures lower than 60 kbar, the continuous wave emission spectrum consists of sharp lines peaking between 600 and 625 nm, related to the ¹D₂→³H₄ transition and three lines at 500, 550 and 650 nm related to emission transitions originating from the ³P₀ level of Pr³⁺. The emission from the ¹D₂ excited state depends weakly on the pressure. Its decay time decreases from 33 μs at ambient pressure to less than 22 μs at 68 kbar. On the other hand, the ³P₀ emission is strongly pressure dependent. At pressures of 60 kbar and higher, the Pr³⁺ emission intensity from the ³P₀ state decreases. This is accompanied by a strong shortening of the luminescence decay time.The observed pressure quenching of the f-f emission transitions and the concomitant lifetime shortening have been attributed to increasing crossover from the ³P₀ state of Pr³⁺ to a Pr³⁺-trapped exciton state.     

Luminescence of Ca(NbO3)2:Pr3+: Pr3+ and self-trapped exciton emission

Photoluminescence and time resolved photoluminescence spectra of Ca(NbO₃)₂ doped with Pr³⁺, excited under 37,000 cm^?1 (270 nm), obtained at high hydrostatic pressure up to 20 kbar applied in a sapphire anvil cells, are presented. At ambient conditions, the emission spectrum obtained in the time interval 0–1 μs is dominated by spin allowed transitions from the ³P₀ state. The luminescence related to transitions from ¹D₂, characterized by a decay time equal to 33 μs, is observed when one excites directly the Pr³⁺ ion with 30,770 cm^?1 (325 nm) wavelength. The introduction of Pr³⁺ impurities in Ca(NbO₃)₂ does not quench the self-trapped exciton (STE) luminescence. This luminescence, peaking at 20,000 cm^?1 (500 nm), having a decay time of 61 ± 1 μs, still occurs when the crystal is excited with a wavelength of 37,000 cm^?1 (270 nm) or shorter. Under such excitation a fraction of the STE luminescence is reabsorbed by Pr³⁺ ions; in this case the emission lifetime of the ¹D₂ → ³H₄ transition of Pr³⁺ is 64 ± 3 μs. This effect is stable also at high pressure.     

Scintillation response of Y3Al5O12:Pr3+ single crystal scintillators

In this paper we present the photoluminescence (PL) and scintillation response of Pr³⁺-doped Y₃Al₅O₁₂ (YAG:Pr) single crystals grown by the Czochralski method with different Pr³⁺ concentrations of 0.16, 0.33, and 0.65 mol%. PL spectra and decay curves were measured for both the fast 5d → 4f and slow 4f → 4f emissions. The PL decay times were evaluated which evidence concentration quenching especially in ¹D₂ → ³H₄ emission for the highest Pr³⁺ concentration. Light yield (LY) of 15,600 photons per MeV and energy resolution of 6.4% at 662 keV γ-rays were obtained with the YAG:Pr (0.33%) crystal. The LY non-proportionality and energy resolution versus γ-ray energy were measured and the intrinsic resolution was calculated. A good proportionality of the LY was found within 7% over the energy range from 1274.5 keV down to 32 keV. The estimated photofraction in the pulse height spectra of 320 and 662 keV γ-rays was also determined and compared with the theoretical one calculated using WinXCom program.     

Luminescent properties and energy transfer of double-emitting NaSrPO4:Eu2+,Tb3+ phosphor for near-UV white LEDs

Novel blue/green NaSrPO₄ phosphors co-doped with Eu²⁺ and Tb³⁺ were synthesized by a conventional solid-state reaction. Their luminescent properties were characterized by using powder X-ray diffraction, photoluminescence excitation and emission spectra, lifetime, and temperature dependent emission spectra, respectively. The NaSrPO₄:Eu²⁺,Tb³⁺,Na⁺ phosphor showed an intense broad excitation band between 250 and 430 nm, which was in agreement with the near-UV chip (350–420 nm), and it exhibited two dominating emission bands at 445 and 545 nm, corresponding to the allowed 4f⁶5d¹→4f⁷(⁸S_7/2) transition of Eu²⁺ ion and the ⁵D₄→⁷F₅ transition of Tb³⁺ ion, respectively. The emission intensity and lifetime of Eu²⁺ ion decreased with the increasing concentration of Tb³⁺ ion, which strongly indicated that an effective energy transfer occurred from Eu²⁺ to Tb³⁺ in NaSrPO₄ host. The principle of the energy transfer should be the combined effect of the non-radiative resonant energy transfer and the phonon-assisted non-radiative process.     

Luminescence kinetics in silica gel doped with Tb3+ ions and ZnS:Mn2+ nanocrystals

Luminescence kinetics and time-resolved luminescence spectra of SiO₂, SiO₂ doped with ZnS:Mn²⁺ nanocrystals and SiO₂ doped with ZnS:Mn²⁺, and additionally co-doped with Tb³⁺, are presented. The purposes of the paper are the analysis of the kinetics of the Tb³⁺ and Mn²⁺ intra-shell luminescence and the elucidation of the energy-transfer mechanism between the ZnS:Mn²⁺ nanocrystals and the Tb³⁺ ions. We have found a blue luminescence related to defects in the ZnS nanocrystals and an intrinsic luminescence of the SiO₂ lattice, which decays in few ns. A yellow luminescence related to the Mn^{2+ 4}T₁(G)→⁶A₁ transition and yellow sharp lines related to the ⁵D₄→⁷F₆, ⁷F₅, ⁷F₄ and ⁷F₃ transitions in Tb³⁺ are found to decay in ms. A very effective energy transfer between ZnS:Mn²⁺ nanoparticles and Tb³⁺ ions has been observed.     

Tb3+掺杂硅酸盐玻璃发光性能的浓度依赖关系

 利用高温熔融法制备了不同浓度的Tb³⁺掺杂硅酸盐玻璃,并分别测量了紫外和X射线激发时的发射光谱。光谱结果表明,不同浓度Tb³⁺掺杂硅酸盐玻璃在紫外和X射线激发时发光行为具有相似的浓度依赖关系：低浓度Tb₄O₇掺杂时主要以蓝光(5D₃→⁷FJ)发射为主,而高浓度掺杂时以绿光(⁵D₄→⁷FJ)发射为主。Tb³⁺发光强度与掺杂浓度的关系分析表明,⁵D₃的浓度猝灭是电偶极-电偶极相互作用引起的, 而⁵D₄的浓度猝灭是交换相互作用引起的。     

Photophysics of RbCl co-doped with Eu2+ and Eu3+

Excitation and luminescence spectra of RbCl co-doped with divalent and trivalent europium ions are reported. Spectral dips appearing in the blue emission from Eu²⁺ are resulted from the radiative energy transfer from Eu²⁺ to Eu³⁺ and consequently induces the luminescence from Eu³⁺ that is responsible for the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions. The induced luminescence has been characterized as a function of temperature and a decay time. In addition, the polarized emission from RbCl doped with only Eu²⁺ is also reported.     

Ultraviolet and visible upconversion emission in Tb3+/Yb3+ co-doped fluorophosphate glasses

Ultraviolet and visible upconversion emissions in Tb³⁺/Yb³⁺ co-doped YF₃–BaF₂–Ba(PO₃)₂ glasses were observed under 980-nm laser diode excitation. The dependence of the emission intensities of Tb³⁺ on the pump power reveals that two-photon processes account for blue cooperative emission of Yb³⁺ at 476 nm and green upconversion emission of Tb³⁺ at 543 nm, and three-photon processes for ultraviolet emission of Tb³⁺ in the wavelength range of 379–435 nm. The effects of Tb³⁺ concentration on the emission intensity and the lifetime of Tb³⁺ and Yb³⁺ are investigated in detail. It is found that the cooperative energy transfer from a pair of excited Yb³⁺ ions to a ground Tb³⁺ ion is responsible for the appearance of blue and green upconversion emissions due to the ⁵D₄→⁷F _J (J=6,5,4,3) transitions of Tb³⁺, and the resonance energy transfer from Yb³⁺ to Tb³⁺ accounts for the population on the ⁵D₃,⁵G₆ level and ultraviolet upconversion emission.     

Cathodoluminescence properties of Tb3+-doped Na3YSi2O7 phosphors

Tb³⁺-doped Na₃YSi₂O₇ phosphors were prepared by the sol–gel method and then characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy, and cathodoluminescence spectroscopy. The XRD results reveal that the Tb³⁺ ions have been introduced as dopants into the Na₃YSi₂O₇ host lattice. Under low-voltage electron beam excitation, the phosphors exhibit the characteristic emissions of Tb³⁺ (⁵ D _3,4→⁷ F _J , J=3–6 transitions). The luminescence color of the phosphors can be tuned from greenish-blue to bluish-green and to green by controlling the Tb³⁺ concentration within the 0.0005–0.15 (x value). The optimum Tb³⁺ doping concentration is 10 mol%, and the “dead voltage” is approximately 1.35 kV. All results indicate that the sample is a phosphor candidate for field-emission displays.     

Synthesis,photoluminescence and thermoluminescence properties of LiNa3P2O7:Tb3+ green emitting phosphor

The alkaline phosphate based LiNa₃P₂O₇:Tb³⁺ phosphors are prepared by solid state reaction method. X-ray diffraction (XRD) analysis shows that all the powders possess orthorhombic structure. Fourier transform infrared (FTIR) spectroscopy studies suggest that the phosphor belong to the diphosphate family. The morphology of the phosphors is identified by scanning electron microscopy (SEM). Upon 378 nm excitation, the LiNa₃P₂O₇:Tb³⁺ phosphors shown emission bands at 482, 545, 588 and 620 nm corresponding to the transitions ⁵D₄→⁷F₆, ⁵D₄→⁷F₅, ⁵D₄→⁷F₄ and ⁵D₄→⁷F₃, respectively. The optimized concentration of Tb³⁺ in LiNa₃P₂O₇ phosphor is found to be 9 mol%. The concentration quenching mechanism was proved to be the exchange interaction between two nearest Tb³⁺ ions with the critical distance (R_c) of 1.18 nm. The Commission International de l'Eclairage (CIE) coordinates evidence that the phosphors emit in the green light region. Thermoluminescence properties of the prepared phosphors are studied by pre-irradiating the powders with different doses of UV irradiation. The kinetic parameters of TL glow curves are calculated using Chen's peak shape method.     

Fluorescent properties of a green- to red-emitting Eu3+, Tb3+ codoped amorphous calcium silicate phosphor

A Eu³⁺, Tb³⁺ codoped amorphous calcium silicate phosphor was prepared by heating a Eu³⁺, Tb³⁺ codoped calcium silicate hydrate phosphor formed by liquid-phase reaction for 30 min at 900 °C. The excitation peak wavelength of the resulting phosphor was 379 nm and the emission peak wavelengths were at 542 nm, attributed to the ⁵D₄→⁷F₅ transition of Tb³⁺, and at 613 mm, attributed to the ⁵D₀→⁷F₁ transition of Eu³⁺. The intensity ratio of the two peaks could be freely controlled by varying the Eu/Tb atomic ratio of the Eu³⁺, Tb³⁺ codoped amorphous calcium silicate phosphor, allowing light to be emitted over a wide range from green to red. It was clarified that electron transfer from Tb³⁺ to Eu³⁺ is occurring.     

Luminescence spectroscopy of Eu3+ and Mn2+ ions in MgGa2O4 spinel

Photoluminescence and excitation spectra of the spinel-type MgGa₂O₄ with 0.5 mol. % Mn²⁺ ions and Eu³⁺ content from 0 to 8 mol. % have been investigated in this work at room temperature. Polycrystalline samples were synthesized via high-temperature solid-state reaction method. Photoluminescence spectra of all samples exhibit host emission presented by a broad “blue” band peaking ∼430 nm, which consists of at least three elementary bands that correspond to different host defects. Excitation of the host luminescence showed the broad band with a maximum at 360 nm. Characteristic bands of d–d transitions of Mn²⁺ ions and f–f transitions of Eu³⁺ ions together with charge-transfer bands (CTB) of these ions were also found on the excitation spectra. Mn²⁺ and Eu³⁺ co-doped samples emit in green and red spectral regions. Mn²⁺ ions are responsible for the green emission band at 505 nm (⁴Т₁→⁶А₁ transition). The studies of photoluminescence spectra of activated samples with different Eu³⁺ ions content show characteristic f–f luminesecence of Eu³⁺ ions. The maximum of Eu³⁺ emission was found at 618 nm (⁵D₀→⁷F₂) and optimal concentration of activator ions was around 4 mol. %.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.     

Fabrication and luminescence properties of Al2O3:Tb3+ microspheres via a microwave solvothermal route

Al₂O₃:Tb³⁺ green phosphors were synthesized via a microwave solvothermal and thermal decomposition route, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra, and decay curves. XRD results indicate that Tb³⁺ doped samples are γ-Al₂O₃ after being calcined at 773 K. SEM results show that the particles of Al₂O₃:Tb³⁺ are hierarchically nanostructured microspheres assembled from nanosheets. The PL spectra indicate that the ⁵D₄→⁷F₅ (545 nm) electric dipole transition is the most intensive when excited at 235 nm. It is shown that 0.7 mol% of doping concentration of Tb³⁺ ions in γ-Al₂O₃:Tb³⁺ is optimum. According to Dexter's theory, the critical distance between Tb³⁺ ions for energy transfer was determined to be 18.4 Å. It is found that the curve followed the single-exponential decay. The excellent chromaticity coordinates of Al₂O₃:Tb³⁺ phosphors, as defined by the International Commission on Illumination (CIE), indicate that it is a good candidate for use in light display systems and optoelectronic devices.     

Enhanced photoluminescence intensity of Y2O3: Eu3+ Sheets by codoping Pr3+ and involved energy transfer mechanisms

Y₂O₃: Eu³⁺ has been widely applied as red phosphors in the fields of displaying and illumination. Here, we report the enhanced luminescence intensity of Y₂O₃: Eu³⁺ by codoping Pr³⁺ ion. The Pr³⁺ and Eu³⁺ doped Y₂O₃ microsheets with high aspect ratio were synthesized by a simple route combining chemical precipitation and pyrolysis, which could emit intense red light centered at 610 nm under the 254 and 365 nm UV excitation. The fluorescence measurement indicated that the luminescence intensity of Y₂O₃: Eu³⁺, Pr³⁺ did not increase monotonously with increasing Pr³⁺ concentration. The highest improvement of the photoluminescence intensity of Y₂O₃:Eu³⁺ was realized in the sample doped with 2 mol% Pr³⁺, which was of 17.8% higher than the whole intensity of only Eu³⁺ doped Y₂O₃.The mechanism analysis based on SEM, XRD, fluorescence spectra, and simplified energy level diagram indicated that (1) energy transfer process between Pr³⁺ and Eu³⁺, (2) crystallinity, and (3) symmetry should respond for this nonmonotonous variation phenomenon by competition with each other. For energy transfer process between Pr³⁺ and Eu³⁺, it was suggested that the cross relaxation of ⁵D₀ + ⁷F₁(Eu³⁺)?³P₀ + ³H₆(Pr³⁺) and the efficient energy transfer from ³P₀ state of Pr³⁺ to ⁵D₁ energy level of Eu³⁺ lead to the improvement of the population of the ⁵D₀ state of Eu³⁺ so that the 610 red emission of Eu³⁺ ion was accordingly enhanced.