Efficient sensitization of Tb3+ emission by Dy3+ in CaMoO4 phosphors: Energy transfer,tunable emission and optical thermometry

Dy³⁺/Tb³⁺ codoped CaMoO₄ phosphors were synthesized by a simple sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The energy transfer process of Dy³⁺→Tb³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results verified that the efficient emission of Tb³⁺ was sensitized by Dy³⁺ under the excitation of 354 nm, realizing tunable emission in CaMoO₄ phosphors. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺: ⁵D₄→⁷F₅ (~546 nm) and Dy³⁺: ⁴F_9/2→⁶H_13/2 (~575 nm). It is expected that the investigated CaMoO₄ nanograins doped with Dy³⁺/Tb³⁺ have prospective applications in display technology and optical thermometry.     

Green luminescence system containing a Tb3+‐β‐diketonate complex doped in the epoxy resin as sensitizer

Photoluminescent properties of the terbium tris(acetylacetonate)tetrahydrated [Tb(acac)₃(H₂O)₄], doped in the epoxy resin, in the solid state are reported. The polymeric Tb³⁺ system and the precursor terbium complex were characterized by elemental analysis, thermogravimetry, differential scanning calorimetry, and infrared and electronic spectroscopy. The excitation and emission spectra of the samples containing the Tb³⁺ complex doped diglycidyl epoxy resin were recorded at 298 and 77 K and exhibited the characteristic bands arising from the ⁵D₄ → ⁷F_J transitions (J = 6–0). The system shows an increase in the luminescence intensity with the increase in the Tb³⁺ complex in the 1, 5, and 10% concentrations due to the energy transfer from the polymer to the rare earth ion. On the other hand, the concentration quenching of luminescence of polymer doped with 15% of the Tb³⁺ complex was observed. The lifetime measurements (τ = 0.81, 0.80, 0.79, and 0.78 ms) decrease with the increase of Tb³⁺‐complex concentration (1, 5, 10, and 15%) doped in polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 865–870, 2004     

Multicolour tunable luminescence of thermal-stable Ce3+/Tb3+/Eu3+-triactivated Ca3Gd(GaO)3(BO3)4 phosphors via Ce3+ → Tb3+ → Eu3+ energy transfer for near-UV WLEDs applications

A series of single-component blue, green and red phosphors have been fabricated based on the Ca₃Gd(GaO)₃(BO₃)₄ host through doping of the Ce³⁺/Tb³⁺/Eu³⁺ ions, and their crystal structure and photoluminescence properties have been discussed in detail. A terbium bridge model via Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer has been studied. The emission colours of the phosphors can be tuned from blue (0.1661, 0.0686) to green (0.3263, 0.4791) and eventually to red (0.5284, 0.4040) under a single 344 nm UV excitation as the result of the Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer. The energy transfer mechanisms of Ce³⁺ → Tb³⁺ and Tb³⁺ → Eu³⁺ were found to be dipole-dipole interactions. Importantly, Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors had high internal quantum efficiency. Moreover, the study on the temperature-dependent emission spectra revealed that the Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors possessed good thermal stability. The above results indicate that the phosphors can be applied into white light-emitting diodes as single-component multi-colour phosphors.     

Energy transfer,tunable emission and optical thermometry in Tb3+/Eu3+ co-doped transparent NaCaPO4 glass ceramics

Tb³⁺/Eu³⁺ co-doped glass ceramics containing NaCaPO₄ nanocrystals were successfully synthesized via traditional melt-quenching route with further heat-treatment and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy. The energy transfer process of Tb³⁺→Eu³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results indicated that the efficient emission of Eu³⁺ was sensitized by Tb³⁺ under the excitation of 378 nm, realizing tunable emission in the transparent bulk glass ceramics containing NaCaPO₄ nanocrystals. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺:⁵D₄→⁷F₅ (~542 nm) and Eu³⁺:⁵D₀→⁷F₂ (~612 nm). The maximum absolute sensitivity of 4.55% K⁻¹ at 293 K and the maximal relative sensitivity of 0.66% K⁻¹ at T=573 K for Tb³⁺/Eu³⁺ co-doped transparent NaCaPO₄ glass ceramic are obtained. It is expected that the investigated transparent NaCaPO₄ glass ceramics doped with Tb³⁺/Eu³⁺ have prospective applications in display technology and optical thermometry.     

Energy transfer and multicolor tunable emission in single-phase Tb3+, Eu3+ co-doped Sr3La(PO4)3 phosphors

A series of green-to-red color-tunable Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors were prepared by high temperature solid-state method. The crystal structures, photoluminescence properties, fluorescence lifetimes, and energy transfer of Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ were systematically investigated in detail. The obtained phosphors show both a green emission from Tb³⁺ and a red emission from Eu³⁺ with considerable intensity under ultraviolet (UV) excitation (~377 nm). The emission colors of the phosphors can be tuned from green (0.304, 0.589) through yellow (0.401, 0.505) and eventually to red (0.557, 0.392) due to efficient Tb³⁺-Eu³⁺ energy transfer (ET). The Tb³⁺→Eu³⁺ energy transfer process was demonstrated to be quadrupole-quadrupole mechanism by Inokuti-Hirayama model, with maximum ET efficiency of 86.3%. The results indicate that the Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors might find potential applications in the field of lighting and displays.     

Visible emission and energy transfer in Tb3+/Dy3+ co-doped phosphate glasses

In this work, we systematically study the spectroscopic properties of Tb³⁺/Dy³⁺ co-doped phosphate glasses in the visible spectral region and explore the sensitization role of Dy³⁺ in the enhancement of visible fluorescence of Tb³⁺ ions. Judd-Ofelt parameters Ω₂ and Ω₄/Ω₆ of the phosphate glass as host for Tb³⁺ are calculated as 21.60 × 10^-20 cm² and 0.73, respectively, based on the measured spectral absorption. Multiple energy transfer (ET) routes from Dy³⁺ to Tb³⁺ and their efficiencies are characterized, and the enhanced fluorescence properties of Tb³⁺ are investigated, including the emission spectral strength and the spontaneous emission lifetime as functions of Dy³⁺ doping concentration. The efficient nonradiative ET processes between Dy³⁺ and Tb³⁺ allow a moderate concentration level of Tb³⁺ to achieve favorably stronger spectral absorption at blue and ultraviolet wavelengths. Tb³⁺/Dy³⁺ co-doped phosphate glass shows promising potential for phosphors and lasing operation at visible wavelengths.     

The luminescence properties,energy transfer mechanism of the color tunable and high quantum efficiency LaAl2.03B4O10.54: Ce3+, Tb3+ phosphors

Tb³⁺ is a typical green emitting luminescence center in inorganic compounds. However, the absorption of Tb³⁺ is very weak in ultraviolet spectral region (from 240 to 400 nm). Ce³⁺ is often used as a sensitizer to transfer energy to Tb³⁺. In this paper, Ce³⁺ and Tb³⁺ were co-doped into a novel aluminates-borates LaAl_2.03B₄O_10.54. Ce³⁺ can absorb UV light (from 240 to 340 nm) and transfer absorbed energy to co-doped Tb³⁺ effectively and bring bright green emission of Tb³⁺. The crystal structure and fluorescence spectra of phosphors, the efficiency of energy transfer between Ce³⁺ and Tb³⁺, decay dynamics, the thermal stability and internal quantum efficiency of luminescence have been investigated in detail. These results indicate that the color tunable LaAl_2.03B₄O_10.54: Ce³⁺, Tb³⁺ phosphor is a potential green-emitting material. Especially, analysis about the relationship of the doping concentration of luminescence centers and thermal stability of luminescence points out a feasible way to enhance the thermal stability of luminescence in the future.     

Energy transfer and control of color luminescence in Dy3+/Tb3+ co-doped transparent oxyfluorosilicate glass ceramics containing LiYF4 nanocrystals

Dy³⁺/Tb³⁺ co-doped oxyfluoride glass ceramics (GC) containing lithium tetrafluoroyttrium (LiYF₄) and yttrium fluoride (YF₃) nanograins were prepared by a traditional melt-quenching approach. The crystalline phases and morphologies of the GCs were investigated. The GCs showed enhanced green emission from Tb³⁺ ions and the quenching of Dy³⁺ emission because of the efficient energy transfer from Dy³⁺ to Tb³⁺ ions. The electric dipole-dipole interactions were responsible for the energy transfer mechanism between Dy³⁺ and Tb³⁺ ions. The energy transfer efficiencies of these glass ceramics were calculated from their decay curves. The Dy³⁺/Tb³⁺ co-doped oxyfluoride GCs with various visible emissions were found to be potential candidates for white-light emitting diode applications.     

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.     

Poly[6‐(2,6‐bis(1′‐methylbenzimidazolyl)pyridin‐4‐yloxy)hexyl acrylate] (PBIP) and its terbium (III) complex (PBIP‐Tb3+): Homopolymerization,optical, and magnetic performance

Poly[6‐(2,6‐bis(1′‐methylbenzimidazolyl)pyridin‐4‐yloxy)hexyl acrylate] (PBIP) and its terbium complex (PBIP‐Tb³⁺) were prepared and characterized by ¹H NMR and FT‐IR. The optical properties of PBIP‐Tb³⁺ complex were characterized by UV–vis spectroscopy and fluorescence spectroscopy. Both polymer PBIP and PBIP‐Tb³⁺ complex show good thermal stability. The magnetic property of PBIP‐Tb³⁺ complex was measured as a function of temperature (5–300 K) at 30 kOe and as a function of an external field (?50 to 50 kOe) at 5 K. Magnetic hysteresis loop of PBIP‐Tb³⁺ complex at 5 K shows typical “S” shape and PBIP‐Tb³⁺ complex is soft ferromagnetic. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44249.     

New apatite-type phosphor Ca9La(PO4)5(SiO4)F2:Tb3+,Dy3+ with improved color rendering index

Ca₉La(PO₄)₅(SiO₄)F₂:Tb³⁺,Dy³⁺ (CLPSF:Tb³⁺,Dy³⁺) phosphors were successfully prepared using the traditional solid-state technique. The crystal structure was refined and the luminescence properties have been examined in detail. The band gap and electronic structure of Ca₉La(PO₄)₅(SiO₄)F₂ were performed by the periodic density functional theory (DFT) calculation. The spectral and fluorescence decay dynamics of CLPSF:Tb³⁺,Dy³⁺ show that the energy transfer behavior between Tb³⁺ and Dy³⁺ ions is observed. The CLPSF:Tb³⁺,Dy³⁺ phosphors can be efficiently excitable at the wavelengths range from 300 to 500 nm. The emission spectrum covers the whole visible part of the spectra with the sharp emission bands in red, green, and blue regions. The correlated color temperature (CCT) and color rendering index (CRI) of white light emission could be improved by the fine-tuning of the Tb³⁺ and Dy³⁺ ions ration in accordance with the energy transfer behavior. Thus, the CLPSF:Tb³⁺,Dy³⁺ phosphor could be used as a material for the near-ultraviolet (n-UV) and white light-emitting diodes (w-LEDs).     

A novel tunable green-to-red emitting phosphor Ca4LaO(BO3)3:Tb,Eu via energy transfer with high quantum yield

A novel green phosphor composed of Ca₄LaO(BO₃)₃:Tb³⁺ (CLBO:Tb) has been synthesized by a combustion method with urea. Its crystal structure, temperature-dependent luminescence, and quantum yield (QY) have been characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra with heating device and integrate sphere. No concentration quenching has been observed when all of La³⁺ ions are substituted with Tb³⁺ ions. Green phosphor Ca₄TbO(BO₃)₃ (CTBO) has 200% luminescence intensity of commercially available phosphor LaPO₄:Ce, Tb (LPO:Ce, Tb) under 378 nm excitation. The QY of CTBO is as high as 98%. Through a Dexter energy transfer mechanism, Eu³⁺ ions are efficiently sensitized by Tb³⁺, resulting in an emission with color tunable from green to red under ultraviolet excitation. A possible mechanism of energy transfer from Tb³⁺ to Eu³⁺ has been investigated by PL spectra and decay measurements. The energy transfer efficiency from Tb³⁺ to Eu³⁺ increases linearly with concentration of Eu³⁺ increasing.     

Tunable emission color of Li2SrSiO4:Tb3+ due to cross‐relaxation process and optical thermometry investigation

A series of Li₂SrSiO₄:xTb³⁺ (0.2%, 0.4%, 0.6%, 0.8%, 2%, 4%, and 6%) phosphors were prepared by conventional solid‐state reaction. It was found that this silicate phosphor has a wide excitation band at near‐ultraviolet region (230‐300 nm) due to spin‐allowed 4f ⁸→4f⁷5d¹ transitions of Tb³⁺ ions, with the exact position dependent on the crystal field of the lattice. The cross‐relaxation process originating from ⁵D₃→⁵D₄ and ⁷F₆→⁷F₀ happened between different Tb³⁺ ions. It leads to the luminescence color of Li₂SrSiO₄: xTb³⁺ tuning from blue to green just by controlling Tb³⁺ concentrations. Furthermore, concentration quenching mechanism, energy migration type, cross‐relaxation rate and efficiency, are discussed in detail. Finally, optical thermometry properties were investigated via temperature‐dependent emission spectra. The results show that low‐concentration‐doped sample (Li₂SrSiO₄:0.4%Tb³⁺) shows remarkable optical thermometry based on fluorescence intensity ratio (FIR) between the blue and green emission of Tb³⁺ ions, whereas the high‐concentration‐doped sample (Li₂SrSiO₄:4%Tb³⁺) demonstrates small emission intensity loss. It illustrates that terbium‐doped silicate phosphor is a multifunctional material with potential application for display field and optical thermometry .     

Synthesis and photoluminescent properties of high-efficient color-tunable Ba3Y2B6O15: Ce3+, Tb3+ phosphors

High-efficient Ce³⁺/Tb³⁺ co-doped Ba₃Y₂B₆O₁₅ phosphors with multi color-emitting were firstly prepared, and their structural and luminescent properties were studied by XRD Rietveld refinement, emission/excitation spectra, fluorescence lifetimes as well as temperature-variable emission spectra. Upon 365?nm excitation, the characteristic blue Ce³⁺ band along with green Tb³⁺ peaks were simultaneously found in the emission spectra. Moreover, by increasing concentration of Tb³⁺, a blue-to-green tunable emitting color could be realized by effective Ce³⁺→Tb³⁺ energy transfer. Furthermore, all Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ phosphors exhibit high internal quantum efficiency of ~?90%, while the temperature-variable emission spectra reveal that the phosphors possess impressive color stability as well as good thermal stability (T₅₀ =?~?120?°C). The results indicate that these efficient color-tuning Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ might be candidate as converted phosphor for UV-excited light-emitting diodes.     

3-Phenyl-4-aroyl-5-isoxazolonate complexes of Tb3+ as promising light-conversion molecular devices

New tris(3-phenyl-4-aroyl-5-isoxazolonate)terbium(III) complexes have been synthesized and characterized by various spectroscopic techniques. Due to an efficient energy transfer from the heterocyclic β-diketonate ligand to the central Tb³⁺, these complexes show a strong emission corresponding to Tb³⁺⁵D₄–⁷F_J (J = 6, 5, 4, 3) transitions, with ⁵D₄–⁷F₅ (545 nm) green emission as the most prominent one. The overall quantum yields and luminescent lifetimes of these complexes were found to be promising as compared to previously reported terbium-1-phenyl-3-methyl-4-acyl-5-pyrazolonate complexes.     

Eu‐, Tb‐, and Dy‐Doped Oxyfluoride Silicate Glasses for LED Applications

Luminescence glass is a potential candidate for the light‐emitting diodes (LEDs) applications. Here, we study the structural and optical properties of the Eu‐, Tb‐, and Dy‐doped oxyfluoride silicate glasses for LEDs by means of X‐ray diffraction, photoluminescence spectra, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (CCTs). The results show that the white light emission can be achieved in Eu/Tb/Dy codoped oxyfluoride silicate glasses under excitation by near‐ultraviolet light due to the simultaneous generation of blue, green, yellow, and red‐light wavelengths from Tb, Dy, and Eu ions. The optical performances can be tuned by varying the glass composition and excitation wavelength. Furthermore, we observed a remarkable emission spectral change for the Tb³⁺ single‐doped oxyfluoride silicate glasses. The ⁵D₃ emission of Tb³⁺ can be suppressed by introducing B₂O₃ into the glass. The conversion of Eu³⁺ to Eu²⁺ takes place in Eu single‐doped oxyfluoride aluminosilicate glasses. The creation of CaF₂ crystals enhances the conversion efficiency. In addition, energy transfers from Dy³⁺ to Tb³⁺ and Tb³⁺ to Eu³⁺ ions occurred in Eu/Tb/Dy codoped glasses, which can be confirmed by analyzing fluorescence spectra and energy level diagrams.     

Tunable Mission and Trichromatic White‐Emitting in Oxyfluoride Glasses by Utilization of Cu+ Ions as Multiple Energy‐Transfer Creators

A series of copper species, Tb³⁺, Mn²⁺ single‐ and co‐doped oxyfluoride glasses were synthesized by a melt‐quenching method. The photoluminescence properties of the glasses containing copper species were demonstrated. Results indicate that the blue‐green emission band peaking at 440 nm was observed, which was ascribed to the photoluminescence of Cu⁺ ions rather than the emissions of Cu²⁺ cations or Cu nano‐particles (Cu NPs) induced by local field effect (LFE) enhancement through surface plasmon resonance (SPR). The interaction mechanisms between Cu⁺ and Tb³⁺/Mn²⁺ have been systematically investigated, and significant enhancement of Cu⁺ emission and the energy‐transfer (ET) efficiencies of Cu⁺→Tb³⁺ and Cu⁺→Mn²⁺ were observed in glasses doped with SnO reducing agent. Furthermore, a wide‐range‐tunable emission and ideal white‐light fluorescence were realized in Cu⁺/Tb³⁺/Mn²⁺‐coactivated glasses by utilization of Cu⁺ cations as dual ET contributors from deep‐UV‐source to multiactivators. Our research further extends the understanding of the interactions between Cu⁺ and Tb³⁺/Mn²⁺ in amorphous materials.     

Photoluminescence Properties of Color‐Tunable Ca3La6(SiO4)6: Ce3+, Tb3+ Phosphors

A series of newly developed color‐tunable Ca₃La₆(SiO₄)₆: Ce³⁺, Tb³⁺ phosphors were successfully prepared in this study. The crystal structures of the prepared phosphors were revealed to be hexagonal with space group P6₃/m, and the lattice parameters were evaluated via utilizing the Rietveld refinement method. Upon excitation at 288 nm, the emission spectra of Ce³⁺and Tb³⁺ ions co‐doped Ca₃La₆(SiO₄)₆ phosphors included a blue emission band and several emission lines. The blue emission band with a peak at 420 nm originated in the f–d transitions of Ce³⁺ ions, and the emission lines in the range of 450–650 nm were assigned to the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. Increasing the doping content of Tb³⁺ ions considerably strengthened Tb³⁺ emission and reduced Ce³⁺ emission owing to the energy transfer from Ce³⁺ to Tb³⁺ ions. The mechanism of the energy transfer was confirmed to be a dipole–dipole interaction. The effective energy transfer from Ce³⁺ to Tb³⁺ ions caused a color shift from purplish‐blue to yellowish‐green. Color‐tunable Ca₃La₆(SiO₄)₆: Ce³⁺, Tb³⁺ phosphors have the potential to be utilized in light‐emitting diodes with proper modulation of the amount of Tb³⁺ ions.     

Preparation,luminescence properties and energy transfer of Ca9Y(PO4)7: Eu2+‐Tb3+ phosphors

Tb³⁺‐doped and Eu²⁺, Tb³⁺ co‐doped Ca₉Y(PO₄)₇ phosphors were synthesized by conventional solid‐state method. Additionally, the luminescence properties, decay behavior and energy transfer mechanism have already been investigated in detail. The green emission intensity of Tb³⁺ ions under NUV excitation is weak due to its spin‐forbidden f‐f transition. While Eu²⁺ can efficiently absorb NUV light and yield broad blue emission, most of which can be absorbed by Tb³⁺ ions. Thus, the emission color can be easily tuned from cyan to green through the energy transfer of Eu²⁺→Tb³⁺ in Ca₉Y(PO₄)₇:Eu²⁺,Tb³⁺ phosphor. In this work, the phenomenon of cross‐relaxation between ⁵D₃ and ⁵D₄ are also mentioned. The energy transfer is confirmed to be resulted from a quadrupole‐quadrupole mechanism.     

Luminescent properties of Gd3+ sensitized low-phonon energy CaGd4O7:Tb3+ green emitting novel phosphors

The trivalent terbium (Tb³⁺) ions activated CaGd₄O₇ (CG) phosphors were synthesized by a sol–gel method. The characterizations were performed after the samples annealed at 1500 °C. The structural and morphological properties were analyzed from the X-ray diffraction patterns and scanning electron microscope images. The photoluminescence excitation spectra showed a broad-band between the wavelengths 250 and 300 nm, which were overlapped with the Gd³⁺ excitation bands. The photoluminescence spectra exhibited efficient green emission due to the sensitization effect of Gd³⁺ ions on the Tb³⁺ ions when exciting with the Gd³⁺ wavelength at 278 nm. In order to analyze the influence of Tb³⁺ concentration on the luminescence behavior of Tb³⁺ ions in the CG host lattice, the decay curves were measured. The temperature-dependent luminescence measurements were done to identify the thermal stability of CG:Tb³⁺ phosphors at elevated temperatures. The cathodoluminescent spectra also showed a similar behavior to that observed in PL spectra. The CIE chromaticity coordinates as a function of Tb³⁺ concentration were calculated and all the obtained chromaticity coordinates have been placed in the green spectral region.