Energy transfer luminescence in (Eu,Nd) : tellurite glass

Here, we bring out an infrared transmitting new optical glass based on TeO₂ added with AlF₃ and LiF, containing dual rare earth ions (Eu³⁺,Nd³⁺) as the dopants with a purpose to examine their luminescence and also the decay times pertaining to a prominent transition of Eu³⁺ (⁵D₀ → ⁷F₂ at 615 nm) as a function of temperature both in the presence and absence of Nd³⁺ ions. The energy transfer rates (W_tr), critical distances (R₀) and transfer efficiencies (η_tr) have been evaluated based on the measured lifetime data of this glass.     

Synthesis and blue to near-infrared quantum cutting of Pr/Yb co-doped Li2TeO4 phosphors

Near-infrared (NIR) quantum cutting luminescent materials Li₂TeO₄ doped with Pr³⁺ and Yb³⁺ were synthesized by solid-state reaction method. The dependence of Yb³⁺ doping concentration on the visible- and NIR-emissions, decay lifetime, and quantum efficiencies of the phosphors are investigated. Quantum cutting down-conversion involving 647 nm red emission and 960-1050 nm broadband near-infrared emission for each 487 nm blue photon absorbed is realized successfully in the resulting phosphors, of which the process of near-infrared quantum cutting could be expressed as ³P₀(Pr³⁺) → ²F_5/2(Yb³⁺) + ²F_5/2(Yb³⁺). The maximum quantum cutting efficiency approaches up to 166.4% in Li₂TeO₄: 0.3 mol%Pr³⁺, 1.8 mol%Yb³⁺ sample corresponding to the 66.4% value of energy transfer efficiency.     

Enhanced luminescence of silica thin films co-doped with Er and Yb

Er³⁺- and Yb³⁺- ions-co-doped silica thin films were prepared by RF magnetron sputtering. Enhanced photoluminescence centered at 1.534 μm was detected at room temperature when excited by a Nd–YAG laser line at 1.064 μm. The photoluminescence intensity increases with Yb-atom doped concentration and tends to saturate at the Yb-atom concentration of 3.0%, indicating that the enhanced photoluminescence results from the energy transfer from Yb³⁺ to Er³⁺.     

Luminescence of Yb, Yb co-doped silica glass for white light source

Yb²⁺, Yb³⁺ co-doped silica glasses were prepared by solid state reaction under vacuum condition for the first time. The luminescence properties of Yb²⁺-doped silica glass were investigated. There are four strong absorption bands in the Ultraviolet (UV) light region due to the 4f¹⁴-4f¹³5d¹ transition of the Yb²⁺ ions. The main emission wavelength of the Yb²⁺-doped silica glass was around 530 nm by the excited wavelength of 398 nm. The full width at half maximum (FWHM) of the excitation and emission bands were 137 nm, 165 nm respectively. The results suggest the Yb²⁺-doped silica glasses may be the potential medium for white light sources based on near UV LED chip.     

Temperature dependence of luminescence behavior in Er/Yb co-doped transparent phosphate glass ceramics

The effect of temperature on the luminescence intensity of up-conversion and near infrared in Er³⁺/Yb³⁺ co-doped phosphate glass ceramics has been investigated. Efficient green and red up-conversion luminescence and strong infrared fluorescence at 1.54 μm wavelength are observed under excitation of 975 nm. The fluorescence intensity is changing at different temperature and the results are explained with the level transitions in Er³⁺/Yb³⁺ co-doped system. Meanwhile, the lifetime of Er³⁺:⁴I_13/2 level corresponding to different operating temperature and pump power is also discussed, and the experimental results are fitted using multiphonon relaxation theory.     

Energy transfer processes in Ce and Tb co-doped Ln2Si2O7 (Ln = Y, Gd)

The Ce³⁺ and Tb³⁺ co-doped Ln₂Si₂O₇ (Ln = Y, Gd) samples were prepared by sol-gel method. Structure characterization of the phosphor was carried out by X-ray diffraction. The luminescence properties of samples were analyzed by measuring the excitation and emission spectra. It was observed that excitation energy can transfer mutually between Ce³⁺ and Tb³⁺ in GPS: Ce³⁺, Tb³⁺ samples, while in Y₂Si₂O₇ :Ce³⁺, Tb³⁺ samples the energy transfer only progresses from Ce³⁺ to Tb³⁺. Based on the energy level diagrams of respective Ce³⁺, Tb³⁺ and Gd³⁺ ion, the detailed pathways for energy transfer are explained.     

Energy transfer and luminescence properties of Eu-doped NaTb(WO4)2 phosphor prepared by a facile hydrothermal method

NaTb_(1−x)Eu_x(WO₄)₂ (x = 0-100%) phosphors have been synthesized via a mild hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation and emission spectra and decay curve were used to characterize the samples. Moreover, the luminescence colors of NaTb_(1−x)Eu_x(WO₄)₂ (NTbW:Eu) samples can be tuned from green, green-yellow, and yellow to red by simply adjusting the relative Eu³⁺-doping concentrations under a single wavelength excitation, which might find potential applications in the light displays systems.     

Partition, luminescence and energy transfer of Er/Yb ions in oxyfluoride glass ceramic containing CaF2 nano-crystals

A complete spectroscopic investigation of energy transfer processes in oxyfluoride glass ceramics containing CaF₂ nano-crystals doped with various amounts of Er³⁺ and Yb³⁺ was reported. An enhancement of the 1.53 μm emission and infrared to visible up-conversion fluorescence was confirmed experimentally due to efficient non-radiative energy transfer from Yb³⁺ to Er³⁺ ions concentrated in CaF₂ nano-crystals. The efficiency of Yb³⁺ to Er³⁺ energy transfer in excess of 85% was obtained for 0.5 mol% Er³⁺/2.0 mol% Yb³⁺ co-doped glass ceramic. Using rate equation formulism, the coefficient of Yb³⁺ to Er³⁺ energy transfer was determined to be about 3.5 times higher than that of Er³⁺ to Yb³⁺ energy back transfer, which is sufficient to provide high ⁴I_11/2 population of Er³⁺ to improve the fluorescence of the co-doped glass ceramics.     

Spectroscopic study of Dy and Dy/Yb ions co-doped in barium fluoroborate glass

Dy³⁺ and Dy³⁺/Yb³⁺ co-doped barium fluoroborate glasses have been synthesized and their luminescence properties have been monitored under UV (355 nm) and NIR (976 nm) excitations, respectively. Absorption spectra of the two samples were recorded and Judd–Ofelt intensity parameters and other radiative parameters were calculated and compared. Dy³⁺ doped sample yields strong yellowish white emission under 355 nm excitation. No emission is observed with 976 nm excitation. The Dy³⁺/Yb³⁺ ions co-doped sample on the other hand gives weak upconversion emission in blue, yellow and red regions on 976 nm excitation via energy transfer process from Yb³⁺ to Dy³⁺ ions from other level. An involvement of three photons has been noted for these emissions. Decay curve for different transitions of these samples have also been recorded and the lifetime of the corresponding levels involved are calculated.     

Single-component and white light-emitting phosphor BaAl2Si2O8: Dy3+, Eu3+ synthesis,luminescence, energy transfer,and tunable color

A series of Dy³⁺ - Eu³⁺ co-doped BaAl₂Si₂O₈ phosphors were prepared via the conventional solid-state reaction method. Their crystal structure, luminescent characteristic and lifetime were investigated. The optimum doping concentrations of Dy³⁺and Eu³⁺ are both 0.05 for Dy³⁺ or Eu³⁺ singly doped BaAl₂Si₂O₈. Furthermore, BaAl₂Si₂O₈: 0.05Dy³⁺ and BaAl₂Si₂O₈: 0.05Eu³⁺ emits yellow and red light. The emission color of BaAl₂Si₂O₈: Dy³⁺, Eu³⁺ could be tuned from yellow to white due to the energy transfer. This energy transfer from Dy³⁺ to Eu³⁺ was confirmed and investigated by photoluminescence spectra and the decay time of energy donor Dy³⁺ ions. With constantly increasing Eu³⁺ concentration, the energy transfer efficiency from Dy³⁺ to Eu³⁺ in BaAl₂Si₂O₈ host increased gradually and reached as high as 81%, the quantum yield was about 47.43%. BaAl₂Si₂O₈: Dy³⁺, Eu³⁺ phosphors can be effectively excited by UV (about 348 nm) light and emit visible light from yellow to white by altering the concentration ratio of Dy³⁺ and Eu³⁺, indicating that the phosphors have potential applications as a white light-emitting phosphor for display and lighting.     

Energy transfer in crystalline Er,Yb:Sc2O3

The use of Yb³⁺ as a sensitizer for Er³⁺ doped laser materials is a common technique because of the high Yb³⁺ absorption cross sections. Energy transfer processes from Yb³⁺ to Er³⁺ in Sc₂O₃ are studied by two different methods. Transfer parameters describing the interactions between Er³⁺ and Yb³⁺ ions are obtained on the one hand from the ratio of emitted photons around 1.55 μm by Er³⁺ ions and around 1 μm by Yb³⁺ ions at cw excitation of Yb³⁺, on the other hand by lifetime measurements of Yb³⁺ ions in the codoped samples. Laser experiments are performed to study the suitability of Er³⁺,Yb³⁺:Sc₂O₃ as a laser material. Comparisons with energy transfer in Er³⁺,Yb³⁺:glass are made.     

Ytterbium sensitization in KY3F10: Pr, Yb for silicon solar cells efficiency enhancement

The codoping of KY₃F₁₀ with Pr³⁺ and Yb³⁺ ions is investigated as a possible quantum cutting system to enhance solar cells efficiency. For one visible photon absorbed by Pr ions, two ytterbium ions are expected to be excited by two consecutive energy transfers. The subsequent emission of two infrared photons reduces thus the thermalization losses usually observed in Si solar cells. Emission spectra and lifetime decays in KY₃F₁₀ doped with 0.5% Pr³⁺ and codoped with 0%, 1%, 10% and 20% Yb³⁺ show an increase of the energy transfer efficiency from Pr³⁺ to Yb³⁺ with the Yb³⁺ concentration. For the first Pr³⁺ to Yb³⁺ energy transfer, an efficiency close to 100% is achieved in KY₃F₁₀: 0.5%Pr³⁺, 20%Yb³⁺. However, this promising result faces challenging issues since an increase in Yb concentration induces energy migration between Yb³⁺ ions which impairs the Yb³⁺ luminescence.     

Synthesis and tunable luminescence of RbCaGd(PO4)2:Ce3+, Mn2+ phosphors

RbCaGd(PO₄)₂ doped with Ce³⁺, Mn²⁺ was synthesized by the sol-gel method. The crystal structure and crystallographic location of Ce³⁺ in RbCaGd(PO₄)₂ were identified by Rietveld refinement. Powder X-ray diffraction (XRD) revealed that the structure of RbCaGd(PO₄)₂:Ce³⁺ compounds is hexagonal structure which is similar to that of hexagonal LnPO₄ with the lattice constant of a = b = 7.005(57) Å, c = 6.352(05) Å, and V (cell volume) = 269.980 Å³. The photoluminescence behavior and emission mechanism were studied systematically by doping activators in the RbCaGd(PO₄)₂ host. The Mn²⁺ incorporated RbCaGd(PO₄)₂:Ce³⁺, Mn²⁺ compounds exhibited blue emission from the parity- and spin-allowed f-d transition of Ce³⁺ and orange-to-red emission from the forbidden ⁴T₁ → ⁶A₁ transition of Mn²⁺. The emission chromaticity coordinates of RbCaGd(PO₄)₂:0.10Ce³⁺, xMn²⁺ (x = 0.16, 0.25) are close to the white region due to an energy transfer process and the energy transfer mechanism from Ce³⁺ to Mn²⁺ in the RbCaGd(PO₄)₂ host was dominated by dipole-dipole interactions.     

Plasmon-enhanced luminescence of YAG: Yb, Er nanopowders by Ag nanoparticles embedded in silicate glass

Solid-state field-assisted diffusion was used to prepare Ag nano-composite silicate glass. After positive diffusion process, small Ag atoms clusters were formed in the slides. The Ag atom clusters could aggregate into Ag nanoparticles (NPs) with bigger size after subsequent reverse diffusion process. YAG: Yb, Er nanopowders were screen-printed on the glass slides after positive and reverse diffusion, respectively, for up-conversion luminescence measurement. Almost no luminescence enhancement was observed for the slide after positive diffusion. Whereas, obvious enhancement was obtained for the slide after reverse diffusion, and the enhancement factor could reach about 26. The strong enhancement was due to the larger size of Ag NPs. The present work suggested a new promising method to enhance the luminescence of YAG: Yb, Er nanopowders.     

Mid-infrared luminescence and energy transfer of Tm/Yb doped fluorophosphate glass

Tm³⁺/Yb³⁺-codoped fluorophosphate glass is prepared by conventional melt-quenching method and the thermal stability of the glass is analyzed. The Judd–Ofelt parameters, radiation emission rates, radiative lifetime and branching ratios of prepared samples are calculated based on the absorption spectra. Upon excitation of a conventional 980 nm laser diode, 1.8 μm emission is obtained from Yb³⁺/Tm³⁺ codoped fluorophosphate. Additionally, the energy transfer between Yb³⁺ and Tm³⁺ ions are quantitatively analyzed. Hence, this Yb³⁺/Tm³⁺ codoped fluorophosphate glass possessing high energy transfer efficiency and excellent thermal stability is a good candidate for efficient 1.8 μm laser.     

Synthesis and luminescence properties of Ca8NaGd(PO4)6F2: Eu2+, Mn2+ for white LEDs

A series of luminescent emission-tunable phosphors Ca₈NaGd(PO₄)₆F₂: Eu²⁺, Mn²⁺ have been prepared by a combustion-assisted synthesis method. The X-ray diffraction measurement results indicate that the crystal structure of the phosphor is a single phase of Ca₈NaGd(PO₄)₆F₂. The photoluminescence (PL) properties of Eu²⁺ and Mn²⁺-codoped Ca₈NaGd(PO₄)₆F₂ phosphors were also investigated. The phosphors can be efficiently excited by ultraviolet (UV) light and show a blue emission band at about 450 nm and a yellow emission band at about 574 nm, which originated from the Eu²⁺ ions and the Mn²⁺ ions, respectively. The efficient energy transfer from the Eu²⁺ ions to the Mn²⁺ ions was observed and its mechanism should be a resonant type via a nonradiative dipole–quadrupole interaction. A color-tunable emission in Ca₈NaGd(PO₄)₆F₂ phosphors can be realized by Eu²⁺ → Mn²⁺ energy transfer. Our results indicate that the developed phosphor may be used as a potential white emitting phosphor for UV based white LEDs.     

Optical properties of the Tm and energy transfer between Tm→Pr ions in P2O5-CaO-SrO-BaO phosphate glass

A P₂O₅-CaO-SrO-BaO phosphate glass doped with Tm³⁺ and glasses doped with (Tm³⁺, Pr³⁺) were used for this study. The photo-luminescence behaviors of Tm³⁺ and Pr³⁺ in phosphate glass were investigated by absorption, excitation and emission spectroscopy. The energy transfer between Tm³⁺ and Pr³⁺ in phosphate glasses (which exhibit a variety of transfer efficiencies) was studied. The experimental quantum efficiencies of the luminescence of Tm³⁺ η₀ and (Tm³⁺, Pr³⁺) doped phosphate glasses were measured to give η/η₀ = 0.447, 0.305, and 0.179 for (0.4 mol% Pr³⁺, 1.0 mol% Tm³⁺), (0.8%Pr³⁺, 1.0%Tm³⁺) and (1.6 mol% Pr³⁺, 1.0 mol% Tm³⁺), respectively. In order to verify the nature of the ion coupling in our phosphate glass system, we applied the Inokuti-Hirayama model. The non-radiative energy transfer rate from Tm³⁺ to Pr³⁺, transfer efficiencies, and the donor-acceptor distance have been calculated and compared with obtained experimental data. As usual, the efficiency and the probability of energy transfer increase with the concentration of the acceptor.     

Upconversion luminescence of Ho sensitized by Yb in transparent glass ceramic embedding BaYF5 nanocrystals

Transparent SiO₂-Al₂O₃-BaCO₃-YF₃-BaF₂ glass ceramics co-doped with Yb³⁺/Ho³⁺ ions were prepared by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscopy observation revealed that BaYF₅ nanocrystals incorporated with Yb³⁺ and Ho³⁺ were precipitated homogeneously among the oxide glass matrix. Three upconversion emission bands centered at 483 nm, 545 nm and 645 nm, corresponding to the ⁵F₃ → ⁵I₈, ⁵S₂, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ respectively, were detected under 976 nm excitation, ascribing to the efficient energy transfer from Yb³⁺ to Ho³⁺. The red emission is prevailing in the precursor glass, while the green one turns to be dominant in the glass ceramic.     

Luminescent properties and energy transfer processes of co-doped Yb–Er poly-crystalline YAG matrix

A poly-crystalline YAG matrix was obtained through the precipitation method; this matrix was single and co-doped with ytterbium and erbium ions, i.e., Yb:YAG, Er:YAG and Yb,Er:YAG. It is found that the measured luminescent properties are similar to those reported for a mono-crystal YAG matrix. In addition, by studying the energy transfer processes in co-doped samples, it is shown that at high erbium concentrations the red emission is enhanced through an up-conversion process that takes place from the ⁴I_13/2 to the ⁴F_9/2 state of erbium ions. This enhanced red emission becomes comparable in intensity to the observed green emission and occurs by pumping at 800 nm through a back energy transfer process.     

Luminescence properties and energy transfer of Ba2Mg(PO4)2:Eu2+, Mn2+ phosphor synthesized by co-precipitation method

The Ba₂Mg(PO₄)₂:Eu²⁺, Mn²⁺ phosphor is synthesized by a co-precipitation method. Crystal phase, morphology, excitation and emission spectra of sample phosphors are analyzed by XRD, SEM and FL, respectively. The results indicate particles synthesized by a co-precipitation method have a smaller size in diameter than that synthesized by conventional solid-state reaction method. Emission spectra of BMP:Eu²⁺, Mn²⁺ phosphor show a broad blue and a broad yellow emission bands with two peaks at about 456 nm and 575 nm under 380 nm excitation. An overlap between Eu²⁺ emission band and Mn²⁺ excitation band proves the existence of energy transfer from Eu²⁺ to Mn²⁺. Emitting color of the BMP:Eu²⁺, Mn²⁺ phosphor could be tuned by adjusting relative contents of Eu²⁺ and Mn²⁺ owing to energy transfer formula. Therefore, BMP:Eu²⁺, Mn²⁺ may be considered as a potential candidate for phosphor for near-UV white LED.