Red Emission Of Eu3 Research Articles

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.

Color tunable emission and low-temperature luminescent sensing of europium and terbium carboxylic acid complexes

A series of lanthanide organic complexes, namely, EuxTb1−x (BTC) (x = 0: complex 1, 0.01: complex 2, 0.05: complex 3, 0.1: complex 4, 0.4: complex 5, 1: complex 6, H3BTC = 1,3,5-benzenetricarboxylic acid), have been synthesized. The overall quantum yields (Φoverall) of luminescence for complex 1 is detected to be as high as 95%, while that for complex 6 is only 8%. It hints the ligand is more suitable to pump Tb3+ ions than Eu3+. Energy transfer from Tb3+ to Eu3+ is observed in Eu, Tb bi-nuclear compounds (complexes 2–5), which leads to tunable emission color from green to yellow, and then to red under the excitation of UV lamp. It indicates them as promising light emitting materials potentially. The temperature dependence of the fluorescence intensity ratio between the green emission of Tb3+ and the red emission of Eu3+ was investigated in the range of 25–300 K for complexes 2–4. The largest relative sensitivity SR is found to be 0.42%K−1, 1.46%K−1 and 0.35%K−1 at 300 K respectively. It hints the binuclear lanthanide complexes could be served as potential optical thermometry materials.

Energy transfer and color tunable emission in Tb3 +,Eu3 + co-doped Sr3LaNa(PO4)3F phosphors

A group of color tunable Sr3LaNa(PO4)3F:Tb3+,Eu3+ phosphors were prepared by conventional high temperature solid state method. The phase structures, luminescence properties, fluorescence lifetimes and energy transfer were investigated in detail. Under 369nm excitation, owing to efficient energy transfer of Tb3+→Eu3+, the emission spectra both have green emission of Tb3+ and red emission of Eu3+. An efficient energy transfer occur in Tb3+, Eu3+ co-doped Sr3LaNa(PO4)3F phosphors. The most possible mechanism of energy transfer is dipole-dipole interaction by Dexter's theoretical model. The energy transfer of Tb3+ and Eu3+ was confirmed by the variations of emission and excitation spectra and Tb3+/Eu3+ decay lifetimes in Sr3LaNa(PO4)3F:Tb3+,Eu3+. The color tone can tuned from yellowish-green through yellow and eventually to reddish-orange with fixed Tb3+ content by changing Eu3+ concentrations. The results show that the prepared Tb3+, Eu3+ co-doped color tunable Sr3LaNa(PO4)3F phosphor can be used for white LED.

Spectral investigations on Eu3+ ,Sm3+ -doped and Sm3+ /Eu3+ co-doped potassium-fluoro-phosphate glass emitting intense orange-red for lighting applications.

Potassium fluoro-phosphate (KFP) glass singly doped with different concentrations of europium (Eu3+ ) or samarium (Sm3+ ) or co-doped (Sm3+ /Eu3+ ) was prepared, and their luminescence spectra were investigated. The phase composition of the product was verified by X-ray diffraction analysis. Optical transition properties of Eu3+ in the studied potassium phosphate glass were evaluated in the framework of the Judd-Ofelt theory. The radiative transition rates (AR ), fluorescence branching ratios (β), stimulated emission cross-sections (σe ) and lifetimes (τexp ) for certain transitions or levels were evaluated. Red emission of Eu3+ was exhibited mainly by the 5 D0 →7 F2 transition located at 612 nm. Concentration quenching and energy transfer were observed from fluorescence spectra and decay curves, respectively. It was found that the lifetimes of the 5 D0 level increased with increase in concentration and then decreased. By co-doping with Sm3+ , energy transfer from Sm3+ to Eu3+ occurred and contributed to the enhancement in emission intensity. Intense orange-red light emission was obtained upon sensitizing with Sm3+ in KFP glass. This approach shows significant promise for use in reddish-orange lighting applications. The optimized properties of the Sm3+ /Eu3+ co-doped potassium phosphate glass might be promising for optical materials.

The study of structural and optical properties of (Eu, La, Sm) codoped ZnO nanoparticles via a chemical route

The (Eu, La, Sm) ions were doped into ZnO nanoparticles by a chemical route, and the substitution of (Eu, La, Sm) for Zn2+ ions was proved by analytic techniques of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscope (TEM), photoluminescence (PL) and UV–vis absorption spectroscopy. The results revealed that the codoping did not change the wurtzite structure of ZnO nanoparticles, but the diameter of the nanoparticles decreased with increasing the rare earth (RE) doping concentrations. The optical bandgaps calculated through UV–visible absorption spectroscopy were found to decrease from 3.26 to 3.14 eV with increasing the RE doping concentrations, which also proved by the slight shift of UV positions in PL spectra. The sharp red emissions located at 578.2, 590.1 and 615.7 nm were originated from the 4f-4f transitions in Eu3+ ions under excitation of 325 nm. And these red emissions of Eu3+ ions showed a strong correlation with the energy storage centers of oxygen vacancies in the samples which was introduced by the other RE ions of La3+ and Sm3+ codoping.

Design, luminescence and energy transfer of single-phased color-tunable YNbO4: Bi3+, Eu3+ phosphor for UV pumped white light-emitting diodes

Single-phased white light-emitting YNbO4: Bi3+, Eu3+ phosphors were synthesized by conventional solid-state reaction. YNbO4: Bi3+ phosphor exhibits a broad excitation band ranging from 220 to 360 nm and a blue light emission band peaking at 457 nm, originating from the 3P1–1S0 transition of Bi3+, whereas YNbO4: Eu3+ phosphor exhibits the typical red emission aroused from the 5D1 → 7F1, 5D1 → 7F2, 5D0 → 7F1, 5D0 → 7F2 transitions of Eu3+. Under the excitation at 330 nm, the YNbO4: Bi3+, Eu3+ exhibits both the blue emission band of Bi3+ and the red emission of Eu3+ due to the energy transfer from Bi3+ to Eu3+ ions. By tuning the Bi3+/Eu3+ ratio via the energy transfer, the emission hue of YNbO4: Bi3+, Eu3+ varied from blue (0.16, 0.18) to white (0.33, 0.24) and eventually to red (0.62, 0.33). The mechanism of energy transfer from a sensitizer Bi3+ to an activator Eu3+ in YNbO4: Bi3+, Eu3+ phosphors was demonstrated to be an exchange interaction.

Promising red emission from functionalized multi walled carbon nanotubes embedded co-doped Bi3++Eu3+: PVA polymer nanocomposites for photonic applications

A bright novel sensitized red emission has been obtained from functionalized multiwalled carbon nanotubes (f-MWCNTs) embedded Bi3++Eu3+: PVA polymer nanocomposites under UV excitation. We have successfully synthesized Eu3+: PVA, Bi3++Eu3+: PVA and Bi3++Eu3++ functionalized MWCNTs: PVA polymer films by traditional solution casting method. The structural and ion-polymer interaction studies have been analysed from XRD and FTIR spectral profiles. Eu3+ doped at different concentrations in PVA polymer films has displayed a red emission at 619nm (5D0→7F2) under 396nm (7F0→5L6) of excitation. Upon co-doping with Bi3+ ions in different concentrations to the Eu3+: PVA polymer film, it exhibits enriched red emission than single Eu3+: PVA under the same excitation due to energy migration from Bi3+ to Eu3+. Successful emission photons of Bi3+ ions are collectively absorbed by the Eu3+ ions which lead the improvement of red emission. In the same fashion, enriched red emission is observed from f-MWCNTs impregnated co-doped Bi3++Eu3+: PVA polymer composites. The red emission of Eu3+ is significantly enhanced in two ways through an efficient energy migration process from Bi3+ to Eu3+ and f-MWCNTs to Eu3+. Possible energy transfer mechanism is clearly demonstrated by several fluorescent methods. From these results, these f-MWCNTs embedded Bi3++Eu3+: PVA polymer films might be recommended as promising candidates for red luminescent materials for photonic devices.

Dazzling red emission from TiO2 nanoparticles impregnated co-doped Gd3++Eu3+: PVA polymer nanocomposites for photonic applications

Abstract Red emission was obtained from rare earth doped polymer nanocomposites, namely, composites of polyvinyl-alcohol (PVA) co-doped with Gd 3+ and Eu 3+ and embedded with TiO 2 nanoparticles (TiO 2 NP), under ultraviolet (UV) excitation. We successfully synthesized Eu 3+ : PVA, Gd 3+ : PVA, (Gd 3+ + Eu 3+ ): PVA, and (Gd 3+ + Eu 3+ + TiO 2 NP): PVA films by solution casting method. From X-ray diffraction patterns and Fourier-transform infrared spectral profiles, the structural details of the films and the ion–polymer interaction mechanism responsible for their formation were systematically analyzed. The thermal stability and decomposition dynamics of the prepared samples were evaluated by thermogravimetry and differential thermal analysis. Pertinent optical absorption bands related to Eu 3+ and Gd 3+ ions in the polymer composites were observed and assigned to the corresponding electronic transitions. The PVA film containing different concentrations of the Eu 3+ dopant displayed red emission at 618 nm ( 5 D 0 → 7 F 2 ) under UV excitation at 396 nm ( 7 F 0 → 5 L 6 ). Upon co-doping with Gd 3+ to form the (Gd 3+ + Eu 3+ ): PVA film, it exhibited red emission that was stronger than that from the singly doped Eu 3+ : PVA film under 270 nm excitation because of the energy transfer from Gd 3+ to Eu 3+ ions. After the TiO 2 nanoparticles were evenly dispersed in the co-doped (Gd 3+ + Eu 3+ ): PVA films, the photoluminescence properties were remarkably enhanced and prominent red emission was observed under 274 nm excitation. The red emission of Eu 3+ was significantly enhanced through an efficient energy-transfer process from the Gd 3+ ions to Eu 3+ ions and from the TiO 2 nanoparticles to Eu 3+ ions. A possible energy-transfer mechanism was clearly demonstrated by several fluorescent methods and lifetime decay dynamics. Based on the above results, these polymer composite films are promising candidates for red luminescent photonic devices.

Morphology evolution of Gd0.99Eu0.01BO3 phosphors synthesized by hydrothermal method with Gd0.99Eu0.01(OH)3 nanorods as sacrificial precursors

Monodisperse mono-concave microsphere/microflower/nanosheet GdBO3:Eu3+ samples have been successfully synthesized via hydrothermal method using Gd0.99Eu0.01(OH)3 nanorods as sacrificial precursors. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field scanning electron microscopy (FE-SEM) and fluorescence spectrometry were used to characterize the samples. The shape of these as-prepared GdBO3:Eu3+ architectures can be tuned effectively by controlling the concentrations of NaOH (CNaOH) of the precursor solution and the amounts of PEG (20000) surfactant. As a typical morphology, the possible formation mechanism for GdBO3:Eu3+ monodisperse mono-concave microsphere was presented in detail. Under ultraviolet excitation, the as-obtained GdBO3:Eu3+ samples showed strong characteristic orange and red emission of Eu3+. Compared with samples get by solid state reaction, the samples obtained by hydrothermal method possess higher red/orange (R/O) ratio attributed to 5D0−7F1 and 5D0−7F2 transitions. The influence of diversity morphology on the R/O ratio and emission intensity has been also investigated. This work sheds some light on the design of a well-defined complex structure, and the luminescent properties have potential applications in fluorescent lamps and field emission displays.

NUV excited luminescence of Eu3+ doped inorganic NaCa0.5Al2B2O7 phosphor via slow evaporation technique

A series of red-emitting alumino-borate phosphors (NCABO) with chemical composition of NaCa0.5Al2B2O7:xEu3+ (0.5–4 mol%) has been synthesized by using slow evaporation technique. X-ray diffraction (XRD), FE-SEM and photoluminescence measurements were performed to testify the crystal structure, surface morphology and luminescent properties. The present phosphor exhibits a strong broad absorption in the near ultraviolet (n-UV) (~395 nm), which is matched well with the emission wavelength of n-UV LED chip. The most intense red emission was found at ~616 nm when doped Eu3+ content was 3 mol%. All the samples show the characteristic red emission of Eu3+ ions (5D0 → 7FJ, J = 0, 1, 2, and 3), suggesting that the phosphor is competitive as a promising red-emitting phosphor for n-UV light-emitting diodes (LEDs). The optimal Eu3+ concentration was determined, and the mechanism of the concentration quenching was predominated by dipole–dipole interaction.

Variable Emission Changes in Bi3+/Ln3+ (Ln = Eu, Sm, Dy) Co-doped Lutetium Vanadates (LuVO4)

High-purity LuVO4: Ln3+/Bi3+ (Ln = Eu, Sm, Dy) phosphors with tetragonal zircon structures were successfully synthesized. The reactions have been carried out by multiple irradiations with very high efficiency. Transmission electron microscope images showed that the phosphors had rod-like structures with average lengths of about 200 nm. The host absorption edge of LuVO4: Ln3+/Bi3+ (Ln = Eu, Sm) shifted to the longer wavelength side. Furthermore, the red emission of Eu3+ ion and the orange emission of Sm3+ ion are remarkably enhanced by encapsulating Bi3+ in LuVO4 system, whereas in the case of LuVO4: Dy3+/Bi3+, the host absorption and the yellow emission from dysprosium have been suppressed in the presence of Bi3+. These novel findings will facilitate their use in the display field.

Radiation Induced Abnormal Reduction of Eu3+ and Luminescence Properties of NaLi2PO4:Eu

Eu 3+ doped NaLi2PO4 sample synthesized via high temperature solid-state reaction exhibits the intense red emission under excitation to wavelength 318 nm light. In the photoluminescence (PL) emission spectra shown usual five emission peaks centered at around 580, 593, 618, 653, and 702 nm corresponding to the allowed transitions 5 D0→ 7 FJ (J = 0, 1, 2, 3, and 4) of Eu 3+ ion. The most prominent peaks were observed at 653 and 702 nm which increased the chromaticity quality followed dark red color with chromaticity coordinate (0.6298, 0.3589) and correlated color temperature (CCT) 1106 K. On exposing to γ-radiation, the red emission of Eu3+ doped NaLi2PO4 phosphor diminished due to the reduction of Eu3+ to Eu2+ ions. The reduction of Eu 3+ → Eu 2+ was examined from the emission spectra of irradiated Eu 3+ doped NaLi2PO4 sample. Tuning the red emission of Eu 3+ doped NaLi2PO4 was observed and calculated the CIE (Commission Internationale de L’Eclairage) chromatic coordinates (chromatic coordinate (x, y), Correlated Color Temperature (CCT) and Duv etc.).

Synthesis and red emission of Eu3+ doped LaBWO6 nanorods

Eu3+ ions doped LaBWO6 phosphors were synthesized by a facile hydrothermal method. The phase, morphology and luminescence properties of the obtained samples were characterized. The XRD, Raman and IR results showed that the obtained samples have the orthorhombic phase, indicating the doped Eu3+ will not change the phase of host. The TEM and SEM images showed that the obtained sample have the rod-like morphology. The excitation spectrum showed that Eu3+ ions doped LaBWO6 phosphors have excitation bands ranging from the ultraviolet region to blue region. The emission spectra showed that Eu3+ ions doped LaBWO6 phosphors emit dominate red light under 281, 394 and 464 nm excitations. And the decay of the red emission fitted well with the double exponential function.

Eu2 + promoted formation of molecule-like Ag and enhanced white luminescence of Ag/Eu-codoped oxyfluoride glasses

The Ag/Eu singly-doped and co-doped glasses were prepared with a melt-quenching method. Silver species are identified as Ag+, molecule-like Ag nano-clusters (Ag NCs) and Ag nano-particles (Ag NPs) with surface plasmonic resonance (SPR) behaviors in the Ag-doped glasses (GAg and GAgEu) by absorption and photoluminescence spectra. Europium ions, including Eu2+ and Eu3+, also existed in the Eu-doped glasses (GEu and GAgEu). The formation of Ag NCs was found to be effectively promoted by an accompanied oxidation of Eu2+. This significantly enhances the super-broad visible emission of the Ag/Eu co-doped glass (GAgEu) by about 8 times than the Ag-doped glass (GAg). Owing to energy transfer from silver species (Ag+ and Ag NCs) to Eu3+, the UV excitation of the Eu3+ red emission was enhanced and extended in 240nm– 400nm region. Combining the bluish white emission of Ag NCs and the red emission of Eu3+, the Ag/Eu co-doped glass (GAgEu) emits pure white light with a low color temperature (CCT) and a high color rendering index (CRI), thus can be a candidate for LED illumination.

Luminescence and energy transfer of single-phase and color-tunable Ca2Y3Sb3O14:Bi3+, Eu3+ phosphor for white light-emitting diodes

Novel single-phase and color-tunable Ca2Y3Sb3O14: Bi3+, Eu3+ phosphors were synthesized by conventional solid-state reaction. The obtained Ca2Y3Sb3O14: Bi3+ phosphor exhibits a blue light emission band peaking at 460 nm due to the 3P1–1S0 transition of Bi3+, whereas Ca2Y3Sb3O14: Eu3+ phosphor exhibits the typical red emission aroused from the 5D0 → 7FJ (J = 0, 1, 2) transitions of Eu3+. Due to the energy transfer from Bi3+ to Eu3+ ions, Ca2Y3Sb3O14: Bi3+, Eu3+ exhibits both the blue emission of Bi3+ and the red emission of Eu3+ under 350 nm excitation. By tuning the Bi3+/Eu3+ ratio, the emission color of Ca2Y3Sb3O14: Bi3+, Eu3+ could vary from blue (0.16, 0.18) to red (0.62, 0.38), and white-light emission with superior CIE chromaticity coordinates (0.35, 0.30) and low correlated color temperature (CCT ≈ 3500 K) was obtained as a result of color tuning. The mechanism of energy transfer from the sensitizer Bi3+ to the activator Eu3+ in Ca2Y3Sb3O14: Bi3+, Eu3+ phosphors was demonstrated to be an exchange interaction.

Synthesis and Luminescence Property of Sr<sub>3</sub>Al<sub>2</sub>O<sub>6</sub>:Eu<sup>3+</sup> Red Phosph or Prepared by Co-Precipitation Technique

Sr3Al2O6:Eu3+ red phosphor was synthesized by co-precipitation and investigated their crystal structures and luminescent properties in detail. EuCl3 was used as rare earth sources to replace Eu2O3, which saving cost significantly. X-ray diffraction(XRD) and scanning electron microscopy (SEM) result indicated that the as-prepared phosphors was calcined at 1150 oC for 2h crystalized in cubic phase with space group of Pa-3 and uniform morphology. The average diameter of the phosphors were 1.8um. Excitation spectrum and emission spectrum results shows when Boric acid was added 3wt% and Eu3+ was added x=0.04((Sr1-xEux)3Al2O6), the red emission of Eu3+ centers was shown at peak of 611nm under near ultraviolet excitation with wavelength of 393nm. The emission spectrum was line spectrum. Luminous intensity achieved the optimum. The thermal quenching experiments indicated that it had thermal stability in the temperature of 20 oC -80 oC.

Repeatable fluorescence switcher of Eu3+-doped CeO2nanorods byl(+)-ascorbic acid and hydrogen peroxide

Inorganic phosphors of Eu3+-doped CeO2 nanorods were synthesized by a hydrothermal method, followed by high temperature calcination. The phosphors with various doping concentrations of Eu3+ exhibited similar rod-like morphology. These phosphors with different Eu3+ contents can be effectively excited at 340 nm due to the charge transfer from O2− to Ce4+, and display orange and red emissions of Eu3+. It was found that the fluorescence intensity of Eu3+-doped CeO2 nanorods was exponentially decreased with increase in the concentrations of L(+)-ascorbic acid, resulting from the chemical reduction of Ce4+ into Ce3+ and the subsequent excitation cut-off of O2− to Ce4+. The fluorescence intensity of reduced phosphors was restored to the original intensity reversibly by adding hydrogen peroxide, which oxidized Ce3+ into Ce4+. The evolution in fluorescence intensity was consistent with surface Ce3+ fractions of Eu3+-doped CeO2 nanorods, which were 22.0% for as-synthesized phosphors, 34.6% for reduced phosphors and 23.2% for restorative phosphors oxidized by H2O2, respectively. The quantitative and repetitive fluorescence switching of Eu3+-doped CeO2 nanorods by adding L(+)-ascorbic acid and hydrogen peroxide alternatively indicates their potential applications as fluorescence switching devices and chemical or biological sensors for detection and monitoring.

Near-white light luminescent material from Eu(III) complexes encapsulated in silica/PMMA matrices

A novel ternary molecular hybrid material has been obtained by immobilization of Eu-Salen complex into silica matrix and poly (methyl methacrylate) (PMMA) matrix. Here, the Salen-type Schiff-base ligand H2Salen (N,N′-bis(salicylidene)ethylenediamine) which has been successfully modified by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) has been used as a flexible linker and the antenna. The obtained solid hybrid material shows not only the characteristic red emission of Eu3+ but also the blue emission of Salen-Si host arising from the inefficient energy transfer from antenna to Eu3+, leading to the unexpected near-white light color of the material. For comparison, the binary hybrid without PMMA has also been prepared. Photoluminescent spectra suggest that the introduction of PMMA can enhance the emission intensity whereas the chromaticity nearly has not been changed. Moreover, thermal analysis has revealed the good thermal stability of the ternary hybrid material. X-ray diffraction patterns demonstrate the amorphous structure of both hybrid materials.

Rapid synthesis and photoluminescence properties of Eu-doped ZnO nanoneedles via facile hydrothermal method

Eu-doped ZnO nanoneedles with different doping concentrations were prepared via the facile hydrothermal method. The crystal structure, morphology and photoluminescence property of the ZnO nanoneedles were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), photoluminescence spectroscopy(PL) and Raman spectroscopy. The results show that the europium ions are incorporated into the crystal lattice of ZnO matrix in trivalent ions. The nanoneedles are 2–3 μm in length and 100 nm in the tip diameter. PL and Raman measurements indicate that higher Eu3+ doping concentration may destroy the crystallization of the nanoneedles and decrease the ratio of I UV/I DLE, which is mainly due to the more defects in the doped ZnO nanoneedles. And the characteristic red emissions of Eu3+ ions are found by the PL spectroscopy with the Eu3+ doping concentration increasing, which are attributed to the 5 D 0→7 F 0, 5 D 0→7 F 1 and 5 D 0→7 F 2 transitions.

Effect of charge compensation on up-conversion and UV excited luminescence of Eu3+ in Yb3+–Eu3+ doped calcium aluminate CaAl4O7

Calcium aluminate powders co-doped with Yb3+ and Eu3+: Ca1−x−yYbxEuyAl4O7 (x = 0.02–0.06; y = 0.02), Ca1−x−yYbxEuyAl4O7 (x = 0.05, y = 0.01–0.07) were synthesized by a modified Pechini citrate process and their optical properties at 298 K and 77 K were investigated. Direct excitation of Yb3+ by means of 2F7/2 → 2F5/2 absorption at 980 nm leads to bluish-green luminescence centered around 488 nm due to the cooperative emission of Yb3+ and red emission of Eu3+ corresponding to 5D0 → 7FJ (J = 0–4) transitions. The near-infrared to red up-conversion luminescence of Eu3+ was assigned to a cooperative sensitization mechanism. The effect of activators concentration and charge compensation by co-doping with Na+ ions on luminescence properties were studied in detail. Na+ addition led to narrowing of luminescence bands, suggesting smaller disturbance/distribution of activator ions local symmetries. This was associated with significantly enhanced luminescence brightness of Eu3+ under UV excitation and, surprisingly, with noticeably reduced efficiency of Eu UC emission upon near-infrared excitation. It was also concluded that Yb3+ pairs transfer preferentially their excitation energy to Eu3+ ions with the local symmetry perturbed by certain defects present in the crystal lattice.