Structural and luminescence properties of silica powders and transparent glass‐ceramics containing LaF3:Eu3+ nanocrystals

In this work, silica powders and transparent glass‐ceramic materials containing LaF₃:Eu³⁺ nanocrystals were synthesized using the low‐temperature sol‐gel technique. Prepared samples were characterized by TG/DSC analysis as well as X‐ray diffraction and IR spectroscopy. The transformation from liquid sols toward bulk powders and xerogels was also examined and analyzed. The optical behavior of prepared Eu³⁺‐doped sol‐gel samples were evaluated based on photoluminescence excitation (PLE: λ_em = 611 nm) and emission (PL: λ_exc = 393 nm, λ_exc = 397 nm) spectra as well as luminescence decay analysis. The series of luminescence lines located within reddish‐orange spectral scope were registered and identified as the intra‐configurational 4f⁶‐4f⁶ transitions originated from Eu³⁺ optically active ions (⁵D₀ → ⁷F_J, J = 0‐4). Moreover, the R/O‐ratio was also calculated to estimate the symmetry in local framework around Eu³⁺ ions. The luminescence spectra and double‐exponential character of decay curves recorded for fabricated nanocrystalline sol‐gel samples (τ₁(⁵D₀) = 2.07 ms, τ₂(⁵D₀) = 8.07 ms and τ₁(⁵D₀) = 0.79 ms, τ₂(⁵D₀) = 9.76 ms for powders and glass‐ceramics, respectively) indicated the successful migration of optically active Eu³⁺ ions from amorphous silica framework to low phonon energy LaF₃ nanocrystal phase.     

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.     

Photoluminescence and optical properties of Eu3+/Eu2+-doped transparent Al2O3 ceramics

Transparent Eu³⁺-doped (0.05–0.15 at. %) alumina ceramics with fine-grained microstructure were prepared and studied in terms of optical properties and photoluminescence (PL). The light transmission through ceramics up to dopant concentrations 0.125 at. % is dominated by birefringence scattering at grain boundaries. As confirmed by HRTEM/EDS element mapping, high photoluminescence intensity was achieved as the result of the dopant segregation at grain boundaries. The PL emission spectra of Al₂O₃:Eu³⁺ ceramics exhibited red light emissions with the highest intensity (394 nm excitation) for material containing 0.125 at. % of Eu³⁺. The luminescence decay was single-exponential with a lifetime ～1.5 ms. The post-sintering reduction of Eu³⁺→Eu²⁺ under an H₂ atmosphere (at 1300 °C) was difficult. Two simultaneously coexisting Eu²⁺ emitting PL centers were identified, one emitting blue light with average decay constant of 150 ns, and the other green light (more intense) with average decay constant of 1.3 μs.     

A Novel Blue‐Emitting Phosphor of Eu2+‐Activated Magnesium Haloborate Mg3B7O13Cl

Eu²⁺‐doped magnesium haloborate Mg₃B₇O₁₃Cl was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction (XRD) measurements and structure refinement. The photoluminescence excitation and emission spectra, and decay curves were measured. Under the excitation of near‐UV light, Eu²⁺‐doped Mg₃B₇O₁₃Cl presents a narrow blue‐emitting band centered at 423 nm. The maximum absolute quantum efficiency (QE) of Mg₃B₇O₁₃Cl:Eu²⁺ phosphor was measured to be 80% excited at 385 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects. Moreover, Mg₃B₇O₁₃Cl:Eu²⁺ phosphor shows scintillation characteristics excited by X‐ray irradiation at room temperature and presents a blue luminescence band with a fast lifetime of 600 ns.     

Site-selective occupation and luminescence property investigation of Ca18Na3Y(PO4)14:Eu2+ phosphor for full-spectrum LED

Cyan-emitting phosphors have attracted widespread attention as an integral part to realize full-spectrum lighting. Understanding the site occupation of luminescence centers is of great importance to design and clarify the luminescent mechanism for new cyan-emitting phosphors. Here, we report a cyan-emitting phosphor Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ synthesized by the high-temperature solid-state method. The crystal structure is characterized by X-ray diffraction and refined by the Rietveld method. The diffuse reflectance spectra, excitation/emission spectra, fluorescence decay curves, thermal stability, and related mechanism are systematically studied. The results show that Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ crystallizes in a trigonal crystal system with space group R3c. Under excitation at 350 nm, a broadband cyan emission can be obtained at 500 nm with a half-width of about 120 nm, which is caused by Eu²⁺ occupying five different sites in host, namely, Na2O₁₂ (450 nm), (Ca3/Na1)O₈ (485 nm), Ca2O₈ (515 nm), Ca1O₇ (565 nm), and (Ca4/Y)O₆ (640 nm), respectively. Moreover, crystal structure, room and low temperature spectroscopy, and luminescence decay time are used to skillfully verify the site-selective occupation of Eu²⁺. Finally, a full-spectrum light-emitting diode (LED) lamp is fabricated with an improved color rendering index (∼90.3), CCT (∼5492 K), and CIE coordinates (0.332, 0.318). The results show that Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ has the potential to act as a cyan emission phosphor for full-spectrum white LEDs.     

Fabrication and characterizations of Eu2+-Dy3+ co-doped SrAl2O4 ceramics with persistent luminescence

(Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ persistent luminescence (PersL) ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) using H₃BO₃ as a sintering additive. The phase composition, microstructure, luminescence properties, trap state, and PersL performance of HIP post-treated (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ PersL ceramics were discussed. For the (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ PersL ceramics after HIP post-treatment, the initial luminescence intensity of the ceramics reached over 6400 mcd/m² with simulated daylight irradiation of 1000 lx for 5 min, and the persistent emission decay time > 17 h. This is much better than the SrAl₂O₄:Eu²⁺,Dy³⁺ PersL powders and the other luminescent ceramics. In addition, this method is a solid-state reactive sintering method for synthesizing ceramics, which has the advantages of low cost and simple operation, and is suitable for large-scale, high-volume industrial production.     

Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu³⁺/Nd³⁺ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF₂+10K₂O +20SiO₂+(49-x) B₂O₃+1Nd₂O₃+xEu₂O₃) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu³⁺ ions in the Nd³⁺ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of ⁷F₀ → ⁵L₆ band (394 nm) with the increasing concentration of Eu³⁺ ion in the Nd³⁺ excitation spectra (λ_emi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd³⁺ ion with the typical excitation wavelengths (Nd³⁺ = 584 nm and Eu³⁺ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE³⁺ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu³⁺ and Nd³⁺ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu³⁺/Nd³⁺ co-doped glasses with other Nd³⁺ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu³⁺ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.     

Synthesis,structural characterization,and photoluminescence properties of Eu3+‐doped Mg3‐xEux(BO3)2 phosphor

Eu³⁺‐doped Mg_3‐xEu_x(BO₃)₂ (x = 0.000, 0.005, 0.010, 0.020, 0.050, and 0.100) phosphors were synthesized for the first time by solution combustion synthesis method, which is a fast synthesis method for obtaining nano‐sized borate powders. The optimization of the synthesis conditions of phosphor materials was performed by TG/DTA method. These phosphors were characterized by XRD, FTIR, SEM‐EDX, and photoluminescence, PL analysis. The XRD analysis exhibited that all of the prepared ceramic compounds have been crystallized in orthorhombic structure with space group Pnnm. Also, the influence of europium dopant ions on unit cell parameters of host material was analyzed using Jana2006 program and the crystalline size was determined by Debye‐Scherrer's formula. The luminescence properties of all Eu³⁺‐doped samples were investigated by excitation and emission spectra. The excitation spectra of Mg_3‐xEu_x(BO₃)₂ phosphors show characteristic peak at 420 nm in addition to other characteristic peaks of Eu³⁺ under emission at 613 nm. The emission spectra of Eu³⁺‐doped samples indicated most intensive red emission band dominated at 630 nm belonging to ⁵D₀→⁷F₂ magnetic dipole transition. Furthermore, the optimum or quenching concentration of Eu³⁺ ion has been determined as x = 0.010 showed the maximum emission intensity when it was excited at 394 nm.     

Impact of Eu3+ Dopants on Optical Spectroscopy of Ce3+: Y3Al5O12‐Embedded Transparent Glass‐Ceramics

Transparent glass‐ceramics containing Ce³⁺: Y₃Al₅O₁₂ phosphors and Eu³⁺ ions were successfully fabricated by a low‐temperature co‐sintering technique to explore their potential application in white light‐emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X‐ray spectroscopy. The impact of co‐sintering temperature, Ce³⁺: Y₃Al₅O₁₂ crystal content and Eu³⁺ doping content on optical properties of glass‐ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass‐ceramics, where Ce³⁺ ions located in YAG crystalline phase while the Eu³⁺ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce³⁺: 5d→4f transition and red luminescence originating from Eu³⁺: 4f→4f transitions. As a result, the quantum yield of the glass‐ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.     

Fabrication and Characterization of Transparent (Y0.98−xTb0.02Eux)2O3 Ceramics with Color‐Tailorable Emission

Transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ (x = 0–0.04) ceramics with color‐tailorable emission have been successfully fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h. These ceramics have the in‐line transmittances of ~73%–76% at 613 nm, the wavelength of Eu³⁺ emission (the ⁵D₀→⁷F₂ transition). Thermodynamic calculation indicates that the Tb⁴⁺ ions in the starting oxide powder can essentially be reduced to Tb³⁺ under ~10^?3 Pa (the pressure for vacuum sintering) when the temperature is above ~394°C. The photoluminescence excitation (PLE) spectra of the transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics exhibit one spin‐forbidden (high‐spin, HS) band at ~323 nm and two spin‐allowed (low‐spin, LS) bands at ~303 and 281 nm. Improved emissions were observed for both Eu³⁺ and Tb³⁺ by varying the excitation wavelength from 270 to 323 nm, without notably changing the color coordinates of the whole emission. The transparent (Y_0.98Tb_0.02)₂O₃ ceramic exhibits the typical green emission of Tb³⁺ at 544 nm (the ⁵D₄→⁷F₅ transition). With increasing Eu³⁺ incorporation, the emission color of the (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics can be precisely tailored from yellowish‐green to reddish‐orange via the effective energy transfer from Tb³⁺ to Eu³⁺ under the excitation with the peak wavelength of the HS band. At the maximum Eu³⁺ emission intensity (x = 0.02), the ceramic shows a high energy‐transfer efficiency of ~85.3%. The fluorescence lifetimes of both the 544 nm Tb³⁺ and 613 nm Eu³⁺ emissions were found to decrease with increasing Eu³⁺ concentration.     

Luminescence of Eu‐Doped Transparent LuPO4 Glass‐Ceramics

Dual valence Eu‐doped transparent glass‐ceramics containing LuPO₄ nanocrystals were fabricated by melt‐quenching technique in air atmosphere. Their luminescent properties were systematically investigated by excitation, emission spectra, and decay lifetime measurements. The prominent Stark splitting, low forced electric‐dipole ⁵D₀ – ⁷F₂ transition and long decay lifetimes of Eu^{3 +} emission for glass‐ceramics reveal the incorporation of Eu^{3 +} into LuPO₄ nanocrystals. The enhanced Eu^{2 +} emission and reduction mechanism of Eu^{3 +} to Eu^{2 +} after crystallization are discussed briefly. Our results indicate that transparent LuPO₄ glass‐ceramics may find applications in photonics.     

Synthesis and Luminescence Properties of Blue‐Emitting Phosphor Eu2+‐Doped Zinc Fluoro‐Phosphate Zn2[PO4]F

Eu²⁺‐doped zinc fluoro‐phosphate Zn₂[PO₄]F was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction measurements and the structure refinement. The photoluminescence excitation and emission spectra, and the decay curves were measured. The natures of the Eu²⁺ emission in inorganic hosts, e.g., the emission and excitation properties, the chromaticity coordinates, the Stokes shifts, the absolute quantum efficiency, and the luminescence thermal stability were reported. Under the excitation of near‐UV light, Eu²⁺‐doped Zn₂[PO₄]F presents a narrow blue‐emitting band centered at 423 nm. The thermal stability of the blue luminescence was evaluated by the luminescence intensities as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects.     

Intense red emission via energy transfer from (Ce3+/Eu3+):P2O5+NaF+CaF2+AlF3 glasses for warm light sources

Europium (Eu³⁺)-doped fluorophosphate (PNCA:P₂O₅+NaF + CaF₂+AlF₃) glasses with the addition of cerium (Ce³⁺) ions were fabricated by the melt-quenching technique to know their ability for the bright red (615 nm) luminescence. The emission (PL) and excitation (PLE) spectra, decay curve measurements as well as energy transfer (ET) process of Ce³⁺→ Eu³⁺ were studied in detail. An excitation spectrum related to the ⁷F₀→ ⁵D₂ level of Eu³⁺ is used to estimate the phonon energy (1121 cm^?1) of the title glass host. Under ultraviolet (UV) irradiation of 299 nm, the PL spectra of (Ce³⁺/Eu³⁺):PNCA glasses show intense red emission at 615 nm whereas the lifetime decrease with respect to increase of Eu³⁺ that could support the observed efficient ET from Ce³⁺ to Eu³⁺. The ET:Ce³⁺ →Eu³⁺ via quadrupole-quadrupole process was confirmed by Reisfeld's approximation and Dexter's ET formula. The ET efficiency (η_ET) and critical distance (R_c) were also calculated. Interestingly, the (Ce³⁺/Eu³⁺):PNCA glasses showed intense red light emission with low correlated color temperatures and the corresponding color purity reached as great as 99%, indicating its potentiality as a red component for warm light sources.     

Luminescent properties of MgAl2O4 ceramics doped with rare earth ions fabricated by spark plasma sintering technique

MgAl₂O₄ ceramics doped with rare earth ions (Eu²⁺ and Ce³⁺ ions) were fabricated by spark plasma sintering technique. A complex characterization of the crystalline and defect structure of the ceramic by XRD was carried out. Absorption, excitation, photo- and cathodoluminescence spectra were studied. The photoluminescence spectrum shifts to the blue region with a maximum at λ_em =?475?nm for the MAS:0.1Ce ceramics. The nature of this luminescence can be caused by the radiative transitions in the cerium ion 5d–4f. The emission spectrum of MAS:0.1Eu has a “green” band emission in range of 400–700?nm centered around 500?nm, which can be ascribed to the allowed 4f⁶5d¹→4f⁷ (5d–4f) transition of Eu²⁺. In the millisecond time range, simultaneously with the emission of the complex host centers, the impurity luminescence bands of the chromium ion are recorded. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63–3.82?eV caused by F-type centers. It was demonstrated that the Eu²⁺ and Ce³⁺ ions lead to change the intensity ratio of the luminescence bands. The luminescence decay kinetics of synthesized spinel ceramics in nano- and millisecond time range were investigated in detail.     

Anomalous preparation,intense 5D0→7F4 emission and adjustable double center emission of Eu3+ and Eu2+ codoped Ca2Al2SiO7

A series of Eu³⁺/Eu²⁺ codoped Ca₂Al₂SiO₇ were synthesized by traditional solid-state synthesis in reducing atmosphere. In this work, XRD powder diffraction proved that the obtained sample was pure. Photoluminescence properties are characterized by excitation, emission spectra and decay curves. Double center emission is achieved by adjusting excitation wavelength and concentration. Under the 394 nm excitation, the emission spectra Ca₂Al₂SiO₇: Eu phosphors exhibit two bands situated at blue emission of 4f5d-4f transition from Eu²⁺ ion and red emission of 4f-4f transition coming from Eu³⁺ ion. The red and yellow light can be obtained when the concentration of doped europium ions is at 0.5% and 1%, respectively. When the excitation wavelength was 394, 280 and 584 nm, the emission color change from yellow to blue, respectively. The bond energy theory explains Eu²⁺ and Eu³⁺ ion occupy Ca1 site in the Ca₂Al₂SiO₇ lattices. In addition, the spectra show that the abnormal intensity peaks of europium ion at 701 nm can be found. Analysis of the related intensity ⁵D₀-⁷F₂(618 nm) transition peak is similar to that of ⁵D₀-⁷F₄(701 nm) transition peak in the emission spectra with the Judd-Ofelt theory.     

Experimental evaluation of the luminescence performance of fired clay brick coated with SrAl2O4:Eu/Dy phosphor

This study evaluates the luminescence performance of fired clay bricks coated with SrAl₂O₄:Eu/Dy phosphor. To do so, SrAl₂O₄:Eu/Dy phosphor was first produced using the traditional solid-state reaction synthesis technique. The prepared phosphor was then used for coating fired clay bricks to analyze the luminescence performance via spectral analysis, decay characteristics, and microstructure of the bricks. The results reveal that excitation and emission spectra of the phosphor coated bricks range from 200 to 480 nm and 455 to 650 nm, respectively, suggesting that the phosphor coated bricks have the capacity of absorbing light with a wide range of wavelengths. The peak wavelength projected at 511 nm in the emission spectrum is achieved, which indicates 4f⁶5 d¹-4f⁷ transition of Europium (Eu²⁺). The repeated excitation and deexcitation of Eu²⁺ by using hole traps and trap levels offered by Dysprosium (Dy³⁺), exist between the ground and the excited state of Eu²⁺ leads to luminescent phenomenon. Moreover, the decay characteristics has revealed that phosphor coated bricks can emit light for a considerable amount of time (>8.5 min) upon the removal of the excitation source. The results reveal that phosphor coated bricks has the potential of increasing energy efficiency of residential and commercial buildings.     

Synthesis and Persistent Luminescence Mechanism of a Novel Orange Emitting Persistent Phosphor Sr5(BO3)3Cl:Eu2+

A series of Eu²⁺‐doped Sr₅(BO₃)₃Cl phosphors were prepared successfully using a conventional solid‐state reaction method. The luminescent properties were studied systematically by utilizing photoluminescence spectra, decay curves, persistent luminescence spectra, and thermoluminescence glow curves. Energy transfer from host to emission center Eu²⁺ was affirmed. The orange persistent luminescence emission was observed for the first time. The optimal doping concentration of Eu²⁺ for persistent luminescence was experimentally to be approximately 0.5% and the orange persistent luminescence duration can persist about 15 min. On the basis of the experimental results, a model was constructed and the relevant mechanism of persistent luminescence was illustrated in detail. Two different ways of trapping the charge carriers were also discussed.     

Sol–gel-deposition of thin TiO2:Eu thermographic phosphor films

A relatively new promising method for surface temperature measurement is the use of thermographic phosphors. For this application, the temperature-dependent luminescence properties of europium (III)-doped anatase (TiO₂:Eu³⁺) thin films were studied. The films were prepared by the sol–gel method using dip coating. The structures and the morphology of the films were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Electron dispersive X-ray spectroscopy (EDX) was used to verify the europium concentration within the films. For using the films as temperature sensors the optical properties are the main concern. Therefore, the emission spectra of the films were measured after ultraviolet laser excitation (355 nm). They indicate that the red characteristic emission (617 nm) of TiO₂:Eu³⁺ due to the ⁵D₀ → ⁷F₂ electric dipole transition is the strongest. The decay time constant of the exponential emission decay under UV excitation with a Nd:YAG laser (355 nm, f = 10 Hz) is strongly temperature dependent in the range from 200 °C up to 400 °C; making it useful for temperature evaluation. The temperature dependence was measured for the emission line at 617 nm; the results demonstrate that anatase doped europium (III) can be used as a thermographic phosphor.     

Synthesis and Photoluminescence of a New Chlorogermanate Phosphor Ca8Mg(GeO4)4Cl2:Eu2+

A new chlorogermanate compound Ca₈Mg(GeO₄)₄Cl₂ (CMGC) was synthesized via high‐temperature solid‐state reaction for the first time. The crystal structure of CMGC had been refined and determined from the XRD profiles by Rietveld refinement method, which belong to space group Fd‐3m with the lattice constants a = b = c = 15.1760(25) Å. Photoluminescence properties of CMGC:Eu²⁺ phosphors were investigated by absorption spectra, excitation, and emission spectra. The occupy situation and energy transfer were investigated by decay lifetimes and emission spectra under different excitation wavelengths. Thermal stability was also measured. The results show that the absorption spectra of CMGC:Eu²⁺ phosphors cover from 250 to 500 nm. Under 365 and 435 nm excitation, the emission spectra of CMGC:Eu²⁺ phosphors show blue‐green (centered at 425 and 510 nm) and green (centered at 510 nm) emission, respectively, which attributed to Eu²⁺ ions occupying different crystal sites. Our results indicated that CMGC:Eu²⁺ phosphors had a potential application use for white light‐emitting diodes.     

Lead fluoride β-PbF2 nanocrystals containing Eu3+ and Tb3+ ions embedded in sol-gel materials: Thermal,structural and optical investigations

Nanocrystalline β-PbF₂ phase singly-doped with Eu³⁺ and Tb³⁺ ions have been successfully synthesized using sol-gel technique and subsequent heat-treatment of xerogels at 350 °C. Thermal behavior and structural properties of obtained materials were studied using thermogravimetric analysis (TG), differential scanning calorimetry (DSC) as well as FT-IR and Raman techniques. XRD results confirmed formation of β-PbF₂ nanocrystals embedded in silica amorphous hosts after annealing at 350 °C. Moreover, the photoluminescence properties have been investigated based on excitation and emission spectra as well as decay analysis from the ⁵D₀ (Eu³⁺) and the ⁵D₄ (Tb³⁺) excited states. The sharp intraconfigurational 4f⁶−4f⁶ and 4f⁸−4f⁸ emission transitions assigned as the ⁵D₀→⁷F_J (J=0–4) of Eu³⁺ and the ⁵D₄→⁷F_J (J=6-3) of Tb³⁺ bands, respectively, were registered. The most prominent bands in studied xerogels and glass-ceramic materials are related to the following electronic transitions: ⁵D₀→⁷F₁ (orange) and ⁵D₀→⁷F₂ (red) (Eu³⁺) as well as ⁵D₄→⁷F₅ (green) and ⁵D₄→⁷F₆ (blue) (Tb³⁺). Thus, the R/O (Eu³⁺) and G/B (Tb³⁺) luminescence intensity ratios were calculated and analyzed. Luminescence decay kinetic clearly indicated a presence of two different surroundings around Eu³⁺ and Tb³⁺ dopants in β-PbF₂-based glass-ceramic samples. In such singly-doped with Eu³⁺ and Tb³⁺ materials, the longer luminescence lifetimes (Eu³⁺: τ₁(⁵D₀)=0.90 ms, τ₂(⁵D₀)=5.15 ms; Tb³⁺: τ₁(⁵D₄)=0.48 ms, τ₂(⁵D₄)=4.01 ms) of an appropriate excited states were achieved in comparison to xerogel hosts (Eu³⁺: τ(⁵D₀)=0.38 ms; Tb³⁺: τ(⁵D₄)=0.49 ms). The obtained results indicate the incorporation of Eu³⁺ and Tb³⁺ ions into nanocrystalline phase during ceramization process.