Synthesis and characterizations of YZ-BDC:Eu3+,Tb3+ nanothermometers for luminescence-based temperature sensing

In the present work, nanothermometers based on amorphous zirconium metal–organic frameworks co-doped with rare-earth ions (YZ-BDC:Eu³⁺,Tb³⁺ nanothermometers) with sizes of about 10–30 nm were successfully synthesized via a microwave-assisted hydrothermal method at 120 °C for 15 min. The determined BET surfaces area, total pore volume and average pore diameter were ∼530 m² g⁻¹, 0.45 cm³ g⁻¹ and 3.4 nm, respectively. Based on Fourier transform infrared spectroscopy (FTIR) and simultaneous thermal analysis (STA) results, the formation process of carboxylic acid salts and the molecular formula of the samples have been proposed. The thermometric properties of Zr-BDC:Eu³⁺,Tb³⁺ nanothermometers and their Y³⁺ ion co-doped counterparts (YZ-BDC:Eu³⁺,Tb³⁺) measured in the 133–573 K temperature range were compared. Moreover, the temperature-dependent CIE(x, y) chromaticity coordinates and emission color of the samples were also determined. As the temperature increased from 133 to 573 K, the emission color of Zr-BDC:Eu³⁺,Tb³⁺ nanothermometers without the presence of Y³⁺ ions changed from orange to red, while for YZ-BDC:Eu³⁺,Tb³⁺ nanothermometers, the emission color changed from yellow to orange, due to the strong effect of the presence of Y³⁺ ions on the luminescence intensity of Eu³⁺ and Tb³⁺ ions. The maximum relative sensitivity (S_Rmax) in both materials was close to 0.5%/K, however, the temperature range of their occurrence was significantly shifted toward higher temperatures due to doping with Y³⁺ ions. The obtained results showed that doping with Y³⁺ ions not only enables the modulation of the useful temperature range with high relative sensitivity, but also provides improved thermal stability.

In the present work, nanothermometers based on amorphous zirconium metal–organic frameworks co-doped with rare-earth ions (YZ-BDC:Eu³⁺,Tb³⁺) with sizes of about 10–30 nm were successfully synthesized via a microwave-assisted hydrothermal method at 120 °C for 15 min.     

Synthesis and photoluminescence characteristics of high color purity Ba3Y4O9:Eu3+ red-emitting phosphors with excellent thermal stability for warm W-LED application

Single phase Eu³⁺-activated Ba₃Y₄O₉ (Ba₃(Y_1−xEu_x)₄O₉) red-emitting phosphors with different Eu³⁺ doping concentrations were synthesized by a high temperature solid-state reaction method. The phase purity, crystal structure, photoluminescence properties, internal quantum efficiency, decay lifetimes, and thermal stability were investigated. Upon excitation at 396 nm near-ultraviolet light and 469 nm blue light, the Ba₃(Y_1−xEu_x)₄O₉ phosphors exhibited a strong red emission at 614 nm due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The optimal doping concentration of Eu³⁺ ions in Ba₃(Y_1−xEu_x)₄O₉ was found to be x = 0.25. Furthermore, the critical distance was calculated to be 12.78 Å and the energy transfer mechanism for the concentration quenching effect was determined to be quadrupole–quadrupole interaction. In addition, the Commission Internationale de I''Eclairage (CIE) chromaticity coordinates of Ba₃(Y_0.75Eu_0.25)₄O₉ phosphors were measured to be (0.6695, 0.3302) which located at the red region, and significantly, the high color purity was about 97.9%. The as-synthesized phosphors also possessed excellent thermal stability and the activation energy was determined to be 0.29 eV. Therefore, the investigated results indicated that the Ba₃Y₄O₉:Eu³⁺ phosphor may be a suitable candidate as a red phosphor for white light-emitting diodes under effective excitation at near-ultraviolet and blue light.

High color purity Ba₃Y₄O₉:Eu³⁺ red-emitting phosphors with excellent thermal stability were developed for warm W-LED application.     

Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity,high quantum efficiency and excellent thermal stability

Eu³⁺-activated Ba₂Y₅B₅O₁₇ (Ba₂Y_5−xEu_xB₅O₁₇; x = 0.1–1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba₂Y_5−xEu_xB₅O₁₇ showed red emission peaking at 616 nm which was attributed to the ⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺ ions. Meanwhile, the influences of different concentrations of Eu³⁺ ions on the PL intensity were also discussed. The optimum concentration of Eu³⁺ ions in the Ba₂Y_5−xEu_xB₅O₁₇ phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole–dipole interaction and the critical distance (R_c) for energy transfer among Eu³⁺ ions was determined to be 5.64 Å. The asymmetry ratio [(⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁)] of Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba₂Y_5−xEu_xB₅O₁₇ phosphors. In addition, the CIE color coordinates of the Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba₂Y_4.2Eu_0.8B₅O₁₇ sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors could be potential candidates for application in near-UV excited white light emitting diodes.

A novel Ba₂Y₅B₅O₁₇:Eu³⁺ red-emitting phosphor with high color purity, high quantum efficiency and excellent thermal stability was developed.     

Luminescence properties and energy transfer investigations of Ba2La2.85−xTb0.15Eux(SiO4)3F multicolor phosphor

The Ba₂La_2.85−xTb_0.15Eu_x(SiO₄)₃F (BLSOF:0.15Tb³⁺, xEu³⁺) multicolor phosphors with apatite structure were synthesized via the solid-state pathway. The crystal structure and luminescence properties of the phosphors were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Rietveld refinement, photoluminescence excitation (PLE) and photoluminescence (PL). The luminescence performance of the phosphor was optimum when the concentration of Tb³⁺ was set to be 0.15 mol and the concentration of Eu³⁺ was set to be 0.22 mol. Under the accurate excitation of 373 nm near ultraviolet (n-UV) light, the emitting color of the phosphors can be tuned from green to red with increasing Eu³⁺/Tb³⁺ ratio. It was further proved that the quadrupole–quadrupole (q–q) interaction is responsible for the energy transfer (ET) in the BLSOF:0.15Tb³⁺, 0.22Eu³⁺ phosphor. Owing to the excellent thermal quenching luminescence property, the BLSOF:0.15Tb³⁺, xEu³⁺ phosphor can be applied in n-UV white light emitting diodes (w-LEDs) and serve as the warm part of warm white light.

The developed phosphors can be accurately excited by 373 nm (n-UV) light and produce a gradient of colors.     

Synthesis and photoluminescence properties of Eu3+-activated LiCa3ZnV3O12 white-emitting phosphors

Single-component white-emitting phosphors are highly promising for applications in phosphor-converted white light-emitting diodes. In this paper, novel single-phase LiCa_3(1−x)ZnV₃O₁₂:Eu³⁺ (x = 0–0.05) phosphors with tunable white emissions were prepared by a conventional solid-state reaction. The LiCa₃ZnV₃O₁₂ (x = 0) phosphor showed an efficient self-activated bluish-green emission due to the V⁵⁺–O²⁻ charge transfer transition of the [VO₄]³⁻ groups, and possessed an intense broad excitation spectrum in the 250–400 nm wavelength range. Together with the [VO₄]³⁻ emission, the red emission of Eu³⁺ ions was also observed in LiCa_3(1−x)ZnV₃O₁₂:Eu³⁺ phosphors. The energy transfer from the [VO₄]³⁻ groups to the Eu³⁺ ions was studied. Importantly, the emission colors of LiCa_3(1−x)ZnV₃O₁₂:Eu³⁺ phosphors varied from greenish-blue to whitish and then to red with increasing Eu³⁺ content and the white-light emission was realized in the single-phase phosphor of LiCa₃ZnV₃O₁₂:0.003Eu³⁺ by combining the [VO₄]³⁻-emission and the Eu³⁺-emission. The energy-transfer efficiency from [VO₄]³⁻ groups to Eu³⁺ ions in the LiCa₃ZnV₃O₁₂:0.003Eu³⁺ sample was determined to be about 52% and the internal quantum efficiency of the LiCa₃ZnV₃O₁₂:0.003Eu³⁺ phosphor was found to be about 41.5%. In addition, the CIE chromaticity coordinates of LiCa₃ZnV₃O₁₂:0.003Eu³⁺ were (x = 0.3374, y = 0.3596), and the correlated color temperature was estimated to be about 5311 K.

A novel high-efficiency white-emitting LiCa₃ZnV₃O₁₂:Eu³⁺ phosphor was developed.     

Structure and luminescence properties of multicolor phosphor Ba2La3(GeO4)3F:Tb3+,Eu3+

A new kind of multicolor phosphor Ba₂La₃(GeO₄)₃F:0.15Tb³⁺,xEu³⁺ (BLGOF:0.15Tb³⁺,xEu³⁺) has been acquired through the traditional high temperature solid phase synthesis method. The structural information of the phosphor was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rietveld refinement. The optical properties of the phosphor have also been studied in detail, including its photoluminescence spectra (PL), photoluminescence excitation spectra (PLE), fluorescence decay curves, energy transfer mechanism and thermal quenching spectra. It has been found that the optimum concentration of Eu³⁺ in BLGOF:0.15Tb³⁺,xEu³⁺ is 0.24 mol and the energy transfer mechanism from Tb³⁺ to Eu³⁺ in BLGOF is quadrupole–quadrupole. The color of BLGOF:0.15Tb³⁺,xEu³⁺ phosphors can be changed from green to yellow/orange to red. Some details of the energy transfer are reviewed and the effect of complex anion regulation on thermal stability has also been studied. All the properties are good and can contribute to the promotion from the laboratory to practical application for the phosphor.

Single-phase Ba₂La₃(GeO₄)₃F:Tb³⁺,Eu³⁺ phosphors were obtained for the first time.     

Eu3+/2+ co-doping system induced by adjusting Al/Y ratio in Eu doped CaYAlO4: preparation,bond energy,site preference and 5D0–7F4 transition intensity

CaY_1−xAl_1+xO₄:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process. XRD patterns indicate that they are pure phase. The photoluminescence properties of the CaY_1−xAl_1+xO₄:2%Eu phosphors exhibit both the blue emission of Eu²⁺ (4f⁶5d¹–4f⁷) and red-orange emission of Eu³⁺ (⁵D₀–⁷F_1,2,3,4) under UV light excitation, which showed that the Eu^3+/2+ co-doping system was obtained by adjusting the Al/Y ratio. Eu³⁺ ions can be reduced to Eu²⁺ ions when the Al/Y ratio was changed. In this work, the bond energy method was used to determine and explain the mechanism of the site occupation of Eu ions entering the host matrix. Also, the emission spectrum showed an unusual comparable intensity ⁵D₀–⁷F₄ transition peak. The relative intensity of ⁵D₀–⁷F₂ and ⁵D₀–⁷F₄ can be stabilized by changing the relative proportions of Al³⁺ and Y³⁺. Furthermore, this was explained by the J–O theory.

CaY_1−xAl_1+xO₄:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process.     

Tunable emission from green to red in the GdSr2AlO5:Tb3+,Eu3+ phosphor via efficient energy transfer

Herein, a series of GdSr₂AlO₅:Tb³⁺,Eu³⁺ phosphors were successfully synthesized through a high temperature solid-state reaction, and their crystal structures as well as photoluminescence properties were investigated in detail. Compared to the intense emission of ⁵D₀ → ⁷F₁ or ⁵D₀ → ⁷F₂ transition of Eu³⁺, another strong emission corresponding to ⁵D₀ → ⁷F₄ was observed. Concentration quenching is not obvious in Tb³⁺ or Eu³⁺-doped GdSr₂AlO₅ because structure isolation and energy transfer (ET) of Gd³⁺ → Eu³⁺ and Gd³⁺ → Tb³⁺ were found. Moreover, the energy transfer process from Tb³⁺ to Eu³⁺ was verified by the overlap of luminescence spectra and the variation of lifetime. Energy transfer mechanism was determined to be a dipole–dipole interaction, and ET efficiency as well as quantum efficiency were also obtained. Moreover, the emission color of GdSr₂AlO₅:Tb³⁺,Eu³⁺ can be tuned from green to red by altering the ratio of Tb³⁺/Eu³⁺. These results indicate that the GdSr₂AlO₅:Tb³⁺,Eu³⁺ phosphor is a promising single-component white light-emitting phosphor.

The emission spectra of GdSr₂AlO₅:2%Tb³⁺,x%Eu³⁺ (x = 0, 0.5, 1, 2, 3, and 5) under 275 nm excitation. (b) Variation tendency of the green emission of Tb³⁺ and the red emission of Eu³⁺.     

Color-tunable photoluminescence and energy transfer of (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solutions for white light emitting diodes

(Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ solid solution phosphors were synthesized by introducing the isostructural Mn₃Al₂(SiO₄)₃ (MAS) into Tb₃Al₅O₁₂:Ce³⁺ (TbAG). Under 456 nm excitation, (Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ shows energy transfers (ET) in the host, which can be obtained from the red emission components to enhance color rendering. Moreover, (Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ (x = 0–0.2) exhibits substantial spectral broadening (68 → 86 nm) due to the 5d → 4f transition of Ce³⁺ and the ⁴T₁ → ⁶A₁ transition of Mn²⁺. The efficiency of energy transfer (η_T, Ce³⁺ → Mn²⁺) gradually increases with increasing Mn²⁺ content, and the value reach approximately 32% at x = 0.2. Namely, the different characteristics of luminescence evolution based on the effect of structural variation by substituting the (MnSi)⁶⁺ pair for the larger (TbAl)⁶⁺ pair. Therefore, with structural evolution, the luminescence of the solid solution phosphors could be tuned from yellow to orange-red, tunable by increasing the content of MAS for the applications of white light emitting diodes (wLED).

(Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ solid solution phosphors were synthesized by introducing the isostructural Mn₃Al₂(SiO₄)₃ (MAS) into Tb₃Al₅O₁₂:Ce³⁺ (TbAG).     

Impact of rare earth (RE3+ = La3+, Sm3+) substitution in the A site perovskite on the structural,and electrical properties of Ba(Zr0.9Ti0.1)O3 ceramics

Undoped Ba(Zr_0.9Ti_0.1)O₃ and rare-earth-doped (Ba_1−xRE_2x/3)(Zr_0.9Ti_0.1)O₃ (RE³⁺ = La³⁺, Sm³⁺) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr_0.9Ti_0.1)O₃ and formation of perovskite structure with the Pm$\bar{3}$m space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure–electrical property relationships.

Undoped Ba(Zr_0.9Ti_0.1)O₃ and rare-earth-doped (Ba_1−xRE_2x/3)(Zr_0.9Ti_0.1)O₃ (RE³⁺ = La³⁺, Sm³⁺) perovskite compounds were synthesized by the conventional solid-state reaction route.     

Combustion derived single phase Y4Al2O9:Tb3+ nanophosphor: crystal chemistry and optical analysis for solid state lighting applications

Cool green light emanating monoclinic Y_4−xAl₂O₉:xTb³⁺ (x = 1–5 mol%) nanophosphors have been fabricated through gel-combustion method. X-ray diffraction and transmission electron-microscopy data have been utilized to assess their structural and microstructural characteristics, including cell parameters and crystallite size. Uneven aggregation of nanoparticles in the nano-scale with distinctive porosity can be seen in the TEM micrograph. Kubelka–Munk model imitative diffuse reflectance spectra and an optical band gap of 5.67 eV for the Y_3.97Al₂O₉:0.03Tb³⁺ nanophosphor revealed high optical quality in the samples, which were thought to be non-conducting. The emission (PL) and excitation (PLE) spectra as well as lifetime measurements have been used to determine the luminescence characteristics of the synthesized nanophosphors. The emission spectra show two color i.e. blue color due to ⁵D₃ → ⁷F_J (J = 4 and 5) transitions and green color due to ⁵D₄ → ⁷F_J (J = 3, 4, 5 and 6) transitions. The most dominant transition (⁵D₄ → ⁷F₅) at 548 nm was responsible for the greenish color in focused nanocrystalline samples. Calculated colorimetric characteristics such as CIE, and CCT along with color purity of the synthesized nanocrystalline materials make them the best candidate for the solid-state lighting (SSL).

Cool green light emanating monoclinic Y_4−xAl₂O₉:xTb³⁺ (x = 1–5 mol%) nanophosphors have been fabricated through gel-combustion method.     

Temperature sensing in Tb3+/Eu3+-based tetranuclear silsesquioxane cages with tunable emission

New luminescent cage-like tetranuclear silsesquioxanes [NEt₄][(Ph₄Si₄O₈)₂(Tb₃Eu)(NO₃)₄(OH)(EtOH)₃(H₂O)]·4(EtOH) (1) and [NEt₄]₂[(Ph₄Si₄O₈)₂(Tb₂Eu₂)(NO₃)₆(EtOH)₂(MeCN)₂]·4(MeCN) (2) present a tunable thermosensitive Tb³⁺-to-Eu³⁺ energy transfer driven by Tb³⁺ and Eu³⁺ emission and may be used as temperature sensors operating in the range 41–100 °C with excellent linearity (R² = 0.9990) and repeatability (>95%). The thermometer performance was evidenced by the maximum relative sensitivity of 0.63% °C⁻¹ achieved at 68 °C.

Tetranuclear silsesquioxane cages with tunable thermosensitive Tb³⁺-to-Eu³⁺ energy transfer were used for temperature sensing based on the Tb³⁺-to-Eu³⁺ emission intensity ratio (LIR) with excellent linearity and sensitivity.     

Unraveling the site-specific energy transfer driven tunable emission characteristics of Eu3+ & Tb3+ co-doped Ca10(PO4)6F2 phosphors

In this study we have explored Ca₁₀(PO₄)₆F₂ as host to develop a variety of phosphor materials with tunable emission and lifetime characteristics based on Eu³⁺ and Tb³⁺ as co-dopant ions and the energy transfer process involved with them. The energy transfer from the excited state of Tb³⁺ ion to the ⁵D₀ state of Eu³⁺ makes it possible to tune the colour characteristics from yellow to orange to red. Further, such energy transfer process is highly dependent on the concentration of Eu³⁺ and Tb³⁺ ions and their site-selective distribution among the two different Ca-sites (CaO₉ and CaO₆F) available. We have carried out DFT based theoretical calculation for both Eu³⁺ and Tb³⁺ ions in order to understand their distribution. It was observed that in cases of co-doped sample, Tb³⁺ ions prefer to occupy the Ca2 site in the CaO₆F network while Eu³⁺ ions prefer Ca1 site in the CaO₉ network. This distribution has significant impact on the lifetime values and the energy transfer process as observed in the experimental photoluminescence lifetime values. We have observed that for the 1^st series of compounds, wherein the concentration Tb³⁺ ions are fixed, the energy transfer from Tb³⁺ ion at Ca2 site to Eu³⁺ ion at Ca1 site is dominating (Tb³⁺@Ca2 → Eu³⁺@Ca1). However, for the 2^nd series of compounds, wherein the concentration Eu³⁺ ions are fixed, the energy transfer process was found to occur from the excited Tb³⁺ ion at Ca1 site to Eu³⁺ ions at both Ca1 and Ca2 (Tb³⁺@Ca1 → Eu³⁺@Ca1 and Tb³⁺@Ca1 → Eu³⁺@Ca2). This is the first reports of its kind on site-specific energy transfer driven colour tunable emission characteristics in Eu³⁺ and Tb³⁺ co-doped Ca₁₀(PO₄)₆F₂ phosphor and it will pave the way for the future development of effective colour tunable phosphor materials based on a single host and same co-dopant ions.

Various site specific energy transfer (ET) process such as Tb³⁺@Ca2 → Eu³⁺@Ca1, Tb³⁺@Ca1 → Eu³⁺@Ca2 and Tb³⁺@Ca1 → Eu³⁺@Ca1 were explored in Eu³⁺ and Tb³⁺ co-doped Ca₁₀(PO₄)₆F₂ phosphor, which are responsible for tunable colour characteristics.     

Synthesis,crystal structures and spectroscopic properties of pure YSb2O4Br and YSb2O4Cl as well as Eu3+- and Tb3+-doped samples

The quaternary halide-containing yttrium(iii) oxidoantimonates(iii) YSb₂O₄Cl and YSb₂O₄Br were synthesised through solid-state reactions from the binary components (Y₂O₃, Sb₂O₃ and YX₃, X = Cl and Br) at 750 °C in evacuated fused silica ampoules with eutectic mixtures of NaX and CsX (X = Cl and Br) as fluxing agents. YSb₂O₄Cl crystallizes tetragonally in the non-centrosymmetric space group P42₁2 with unit-cell parameters of a = 773.56(4) pm and c = 878.91(6) pm, whereas YSb₂O₄Br is monoclinic (space group: P2₁/c) with a = 896.54(6) pm, b = 780.23(5) pm, c = 779.61(5) pm and β = 91.398(3)°, both for Z = 4. The two new YSb₂O₄X compounds contain [YO₈]¹³⁻ polyhedra, which are connected via four common edges to form layers (d(Y³⁺–O²⁻) = 225–254 pm) without any Y³⁺⋯X⁻ bonds (d(Y³⁺⋯X⁻) > 400 pm). Moreover, all oxygen atoms belong to ψ¹-tetrahedral [SbO₃]³⁻ units, which are either connected to four-membered rings [Sb₄O₈]⁴⁻ in the chloride (Y₂[Sb₄O₈]Cl₂ for Z = 2) or endless chains in the bromide (Y_1/2(SbO₂)Br_1/2 for Z = 8) by common vertices. With distances of 307 pm in YSb₂O₄Cl and 326 pm in YSb₂O₄Br there are not even substantial bonding Sb³⁺⋯X⁻ (X = Cl and Br) interactions at work. Luminescence spectroscopy on samples doped with trivalent europium and terbium showed an energy transfer from the oxidoantimonate(iii) moieties as the sensitizer in the host structure onto the lanthanoid activators.

The oxygen atoms of the two new compounds belong to ψ₁-tetrahedral [SbO₃]³⁻ units, which are either vertex-connected to four-membered rings in YSb₂O₄Cl or to endless chains in YSb₂O₄Br. Eu³⁺- and Tb³⁺-doped samples show red or green luminescence.     

Energy transfer between rare earths in layered rare-earth hydroxides

Energy transfer between rare earths in layered rare-earth hydroxides (LRHs) is worth the intensive study because the hydroxyls that act as the bridge connecting the neighbouring rare earths would generate non-radiative transitions. This study focuses on the energy transfer in the intralayer and the adjacent layers of LRHs. A series of LEu_xTb_1−xHs (x = 0, 0.05, 0.2, 0.5, 0.8, and 0.95) was synthesized, the basal spacing (d_basal) was adjusted from 8.3 to 46 Å through ion-exchange process, and unilamellar nanosheets were prepared through a delamination process. The luminescence behaviours of the samples demonstrated the following: (1) for the delaminated nanosheets, the quenching effect of both Eu³⁺ and Tb³⁺ was hardly observed. This implies that in the intralayer, the efficiency of energy transfer is extremely low, so that highly-concentrated co-doping does not influence the luminescence and by controlling the Eu/Tb molar ratio, white light can be obtained. (2) For small d_basal, e.g., 27 Å, the fluorescence quenching of Tb³⁺ and Eu³⁺ was remarkable, while for large d_basal, e.g., 46 Å, the emission of Tb³⁺ emerged and the self-quenching between Eu³⁺ ions weakened. (3) The energy transfer efficiency deceased with an increase in the distance between adjacent layers. In other words, either the energy transfer between Eu³⁺ and Tb³⁺ or the energy migration between Eu³⁺ ions was more efficient when they were located in adjacent layers than in intralayers even when they were the nearest neighbours.

In LRHs, the energy transfer between rare earths in adjacent layers was more efficient than that between neighboring rare earths in intralayers.     

Luminescence properties and energy transfer of K3LuF6:Tb3+,Eu3+ multicolor phosphors with a cryolite structure

In recent years, compounds with a cryolite structure have become excellent hosts for luminescent materials. In this paper, Tb³⁺ doped and Tb³⁺/Eu³⁺ co-doped K₃LuF₆ phosphors were prepared via a high temperature solid phase sintering method. The XRD, SEM, as well as photoluminescence excitation (PLE) and emission (PL) spectra were measured to investigate the structure and luminescence properties of the as-prepared samples. In the Tb³⁺/Eu³⁺ co-doped K₃LuF₆ samples, both characteristic emission spectra of Tb³⁺ and Eu³⁺ could be observed and the emission color of the K₃LuF₆:0.12Tb³⁺,xEu³⁺ phosphors could be adjusted from green to yellowish pink and the corresponding CIE values could be regulated from (0.2781, 0.5407) in the green area to (0.4331, 0.3556) in the yellowish pink area by controlling the concentration ratio of Eu³⁺/Tb³⁺. In addition, the energy transfer mechanism in Tb³⁺/Eu³⁺ co-doped K₃LuF₆ was calculated to be a quadrupole–quadrupole interaction from Tb³⁺ to Eu³⁺ based on the Dexter''s equation.

Single-phase multicolor phosphors with a cryolite structure were obtained via energy transfer from Tb³⁺ to Eu³⁺.     

Tb3+ and Sm3+ co-doped Ca2La3(SiO4)3F phosphor: synthesis,color regulation,and luminescence properties

The polychromatic phosphor with an apatite structure Ca₂La₃(SiO₄)₃F:0.15Tb³⁺,xSm³⁺ (CLSOF:0.15Tb³⁺,xSm³⁺) was synthesized via a solid-state route. The phase and morphology of the phosphor has been investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The structures of the as-prepared phosphor were verified by means of the Rietveld method. The optical performance was investigated thoroughly and the phosphors could emit multicolor light from short wavelengths to long wavelengths by gradually increasing the doping contents of samarium. All the results support that the energy transfer in CLSOF:0.15Tb³⁺,xSm³⁺ contributes to the color tunable property of the phosphor.

The photoluminescence spectra of Ca₂La_2.85−x(SiO₄)₃F:0.15Tb³⁺,xSm³⁺ phosphors (left) could emit typical multicolor light with increasing doping contents of samarium (right).     

Size dependent optical temperature sensing properties of Y2O3: Tb3+, Eu3+ nanophosphors

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The sizes of the sample particles were controlled by changing the molar ratio of the urea and rare earth ions. The microstructure and crystallographic structure of the sample were determined through powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FE-SEM). The test results show that the sample is body centered cubic. As the molar ratio of urea to rare earth ions increases, the size of the sample particles decreases. The temperature-dependent emission spectra of Tb³⁺, Eu³⁺ co-doped Y₂O₃ phosphors with different particle sizes were measured. The results showed that because the fluorescence intensity ratio (FIR) of Tb³⁺ and Eu³⁺ varies with temperature, it can be used to visually reflect changes in temperature. In addition, the temperature sensing sensitivity of Tb³⁺ and Eu³⁺ co-doped Y₂O₃ phosphors increased upon a decrease in the particle size, but the relative sensitivity decreased with a decrease in the particle size. The physical mechanism of the sensitivity and relative sensitivity changes with the size of the sample particles was also explained.

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The size dependence-optical temperature sensing properties of nanophosphors have been studied.     

Structure,tunable luminescence and energy transfer in Tb3+ and Eu3+ codoped Ba3InB9O18 phosphors

The borate Ba₃InB₉O₁₈ (BIBO) is a promising host material for phosphors. A series of Tb³⁺ and Eu³⁺ codoped Ba₃InB₉O₁₈ phosphors were synthesized. Based on the Rietveld method, structure refinement of the codoped BIBO phosphor was carried out. Then, the luminescence properties of BIBO:Tb³⁺, Eu³⁺ phosphors were extensively investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. The measured PL spectra and decay times evidenced that energy transfer occurs between the Tb³⁺ and Eu³⁺ ions. The energy-transfer mechanism from Tb³⁺ to Eu³⁺ in Ba₃InB₉O₁₈ is dominated by electric multipolar interactions, with the critical distance calculated to be 10.97 Å. The temperature sensitivity of the Tb³⁺ and Eu³⁺ codoped sample under VUV was also investigated at the low temperature range from 25 K to 298 K. The emission color could be tuned from green to the red region by adjusting the concentration of codoped ions. The results indicate that the BIBO-based phosphors are valuable candidates for applications in the display and lighting fields.

The emission colors of Ba₃InB₉O₁₈:Tb³⁺, Eu³⁺ can be adjusted from yellowish green to orange by tuning the content of Eu³⁺ ions due to the energy transfer from Tb³⁺ to Eu³⁺, thus showing a great potential for display and lighting fields applications.