Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

Spinel (MgAl₂O₄) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al₂O₃, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn²⁺ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.     

The effect of Eu3+ concentration on the Y2O3 host lattice obtained from citrate precursors

This work presents a thermal decomposition study of the precursor resin prepared from the citrate precursor along with structural features and optical properties materials composed by Y₂O₃ and Eu³⁺ containing Y₂O₃ in 0.5, 3, 5 and 7 mol%. The microcrystallite sizes were estimated from the Scherrer equation. The structural and optical properties revealed that the addition of 5 mol% of Eu³⁺ to the Y₂O₃ matrix gave rise to the highest relative emission intensity which was evidenced by the luminescence intensity. The lifetime of the 0.5 mol% Eu³⁺-doped sample suggested two different symmetry sites for Eu³⁺ ions because two different lifetime values were acquired for this sample, while for phosphors doped with 3 or 5 mol% of Eu³⁺ ions only one similar lifetime was observed. When the concentration of Eu³⁺ is 0.5 and 3 mol%, the luminescence intensity is weak due to the low probability of the O^2? - Eu³⁺ charge transfer transition. On the other hand, when the concentration of the Eu³⁺ ions is 7 mol%, a quenching effect is evidenced.     

Nature of intrinsic and impure luminescence of MAlP2O7 crystals

The results of the photoluminescence (PL) investigation of pure and chromium-doped MAlP₂O₇ (M = Na, K, Cs) compounds are presented. The spectra of the intrinsic luminescence of MAlP₂O₇ crystals consist of a separated UV band at a peak position near 330 nm and a complex wide band which covers the region of visible light up to 750 nm at excitation by VUV synchrotron radiation. The “red” band in 600–1000 nm diapason appears in the PL spectra of crystals doped with chromium ions. The effect of the temperature on the structure, the peak positions and intensities of the luminescence bands was studied. An assumption about the nature of the intrinsic PL was made. The “red” luminescence was considered as a result of the ⁴Т₂ → ⁴А₂ radiation transitions in the impurity Cr³⁺ ions located in the intermediate crystal field.     

Optical studies on X and γ irradiated vacuum grown CsBrI:Eu2+ crystals

CsBr_0.9I_0.1:Eu²⁺ crystals were grown by Bridgman technique. Optical absorption spectrum of the unirradiated CsBr_0.9I_0.1:Eu²⁺ crystals show absorption bands at 270 nm and 340 nm. Irradiated CsBr_0.9I_0.1:Eu²⁺ shows single F band for F(Br⁻) and F(I⁻) centers at 730 nm. Conversion of Eu²⁺ to Eu³⁺ after irradiation is confirmed by optical absorption technique. Sharp and single Photoluminescence (PL) emission band is observed at 440 nm for CsBr_0.9I_0.1:Eu²⁺ crystals. Photostimulated Luminescence (PSL) emission band observed for CsBr_0.9I_0.1:Eu²⁺ crystals at 442 nm due to excitation at 730 nm shows that the F centers are photostimulable. PSL emission intensity increases linearly with irradiation dose up to 2.5 Krad.     

Synthesis and spectroscopic characterization of the K4BaSi3O9:Eu3+

K₄BaSi₃O₉:Eu³⁺ polycrystals were synthesized by solid state method. X-ray powder diffraction measurements confirmed structure of the samples. The excitation and the emission spectra of orthorhombic K₄BaSi₃O₉ doped with Eu³⁺ were investigated. The excitation spectrum exhibits a broad band with maximum at 220 nm corresponding to the charge transfer (CT) transition between O²⁻ and Eu³⁺ ions and smaller 4f–4f transitions. The emission of investigated phosphor was excited at 395 nm and has quantum efficiency (QE) equal 27%. The emission maximum at 616.5 nm was assigned to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The luminescence decay profiles as well as the thermal quenching were measured and analyzed. K₄BaSi₃O₉:Eu³⁺has high temperature quenching of the emission T_0.5 = 335 °C.     

Crystal growth and photoluminescence characteristics of Ca2MgSi2O7:Eu3+ thin films grown by pulsed laser deposition

Ca₂MgSi₂O₇:Eu³⁺ films were deposited on Al₂O₃ (0 0 0 1) substrates by pulsed laser deposition. The films were grown at various oxygen pressures ranging from 100 to 400 mTorr. The crystallinity and surface morphology of the films were examined by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD and AFM respectively showed that the Ca₂MgSi₂O₇:Eu³⁺ films had a zircon structure and consisted of homogeneous grains ranging from 100 to 400 nm depending on the deposition conditions. The radiation emitted was dominated by a red emission peak at 620 nm. The maximum PL intensity of the Ca₂MgSi₂O₇:Eu³⁺ films grown at 300 mTorr was increased by a factor of 1.3 compared to that of Ca₂MgSi₂O₇:Eu³⁺ films grown at 100 mTorr. The crystallinity, surface roughness and photoluminescence of the thin-film phosphors were strongly dependent on the deposition conditions, in particular, the oxygen partial pressure.     

Synthesis,characterization and luminescence of Sr3Al2O6 phosphor with trivalent rare earth dopant

The luminescent properties of Sr₃Al₂O₆ doped and co-doped with the rare earths (Ln³⁺ = Eu³⁺, Dy³⁺, Eu³⁺ and Dy³⁺) have been studied. The material was synthesized by reflux method and fired up to 900 °C for 16 h. The X-ray diffraction pattern confirms that the synthesized material consists of Sr₃Al₂O₆ as main phase. The photoluminescence study gives a clear evidence of europium stabilizing in trivalent form and surprisingly with no presence of europium in the divalent state. The addition of Dy³⁺ as co-dopant in the Sr₃Al₂O₆:Eu³⁺ matrix shows the quenching effect in the photoluminescence (PL) spectra. The photoluminescence intensity of Eu³⁺ falls gradually on increasing the concentration of the co-dopant in the range from 0.1 mole% to 2.0 mole%. The significantly intense thermoluminescence (TL) glow peak was obtained for Sr₃Al₂O₆:Eu³⁺, Dy³⁺ (1% and 0.1%) at around 194 °C when irradiated with 10 kGy dose from Sr-90 β source.     

Effects of rare-earth concentration and heat-treatment on the structural and luminescence properties of europium-doped zirconia sol–gel planar waveguides

Sol–gel zirconia films doped with Eu³⁺ concentrations ranging from 0.2% to 10%, were prepared by dip-coating a solution of the starting precursor, zirconium n-propoxide, ethanol, methanol, water, acetic acid and europium nitrate on glass and SiO₂/Si wafer substrates. The ZrO₂ sol thus synthesized remains stable for several months. Structural characterization of the zirconia films was performed using Waveguide Raman Spectroscopy. These films present an amorphous phase up to an annealing temperature of 400 °C. Above 400 °C the matrix evolves towards a metastable tetragonal phase. This transformation was found to depend on the concentration of Eu³⁺ ions. Indeed, while for samples doped with 0.2% Eu³⁺ this transformation occurs around 450 °C, in the case of 10% of Eu³⁺ ions, the transition is pushed off to 500 °C. The optical losses of these waveguides were found to be about 0.3 dB cm⁻¹ for samples annealed at 400 °C. The surfaces of the films were characterized using Atomic Force Microscopy and the roughness was measured. The Eu-doped films were investigated using Waveguide Photoluminescence Spectroscopy. The dynamical behaviour of the Eu³⁺ emissions indicated that concentration quenching effect is not observed even when the matrix is doped up to 10%.     

Al2O3:Cr3+ microfibers by hydrothermal route: Luminescence properties

Uniform Al₂O₃:Cr³⁺ microfibers were synthesized by using a hydrothermal route and thermal decomposition of a precursor of Cr³⁺ doped ammonium aluminum hydroxide carbonate (denoted as AAHC), and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD indicated that Cr³⁺ doped samples calcined at 1473 K were the most of α-Al₂O₃ phase. SEM showed that the length and diameter of these Cr³⁺ doped alumina microfibers were about 3–9 μm and 300 nm, respectively. PL spectra showed that the Al₂O₃:Cr³⁺ microfibers presented a broad R band at 696 nm. It is shown that the 0.07 mol% of doping concentration of Cr³⁺ ions in α-Al₂O₃:Cr³⁺ was optimum. According to Dexter's theory, the critical distance between Cr³⁺ ions for energy transfer was determined to be 38 Å. It is found that the curve followed the single-exponential decay.     

CaAlSiN3:Eu2+ phosphors bonding with bismuth borate glass for high power light excitation

The CaAlSiN₃:Eu²⁺ red phosphor-in-glass was prepared using bismuth borate glass as the binder for high power light excitation. B₂O₃–Bi₂O₃–Al₂O₃–ZnO glass powder showed good sintering behavior with CaAlSiN₃:Eu²⁺ phosphors at around 550 °C. The phosphor-in-glass has flat surface with a thickness of about 100 μm. From the images of FE-SEM and confocal laser scanning microscope, the uniform distribution of phosphor particles inside the phosphor-in-glass was vividly and clearly observed. And the luminescent property of phosphors was not greatly affected by glasses, as shown in fluorescence spectra. When the volume radio of CaAlSiN₃:Eu²⁺ phosphors was 50%, the sample exhibited low thermal quenching and high flexural strength of 28.5 MPa. Compared YAG:Ce³⁺ phosphor-in-glass with CaAlSiN₃:Eu²⁺ phosphor-in-glass, we found bismuth borate glass had better wettability on YAG:Ce³⁺ particles, which caused a higher flexural strength of the YAG:Ce³⁺ phosphor-in-glass.     

Spectroscopic investigations on Eu3+ ions in Li–K–Zn fluorotellurite glasses

Eu³⁺ ions incorporated Li–K–Zn fluorotellurite glasses, (70 − x)TeO₂ + 10Li₂O + 10K₂O + 10ZnF₂ + xEu₂O₃, (0 ⩽ x ⩽ 2 mol%) were prepared via melt quenching technique. Optical absorption from ⁷F₀ and ⁷F₁ levels of the Eu³⁺-doped glass has been studied to examine the covalent bonding characteristics, energy band gap and Judd–Ofelt intensity parameters. The emission spectra (⁵D₀ → ⁷F_0,1,2,3,4) of the glasses were used to estimate the luminescence enhancement, asymmetric environment in the vicinity of Eu³⁺ ions, stimulated emission cross section and branching ratios. The phonon side band mechanism of ⁵D₂ level of the Eu³⁺ ions in the prepared glass was examined by considering the excitation and Raman spectra. The radiative lifetime calculated using Judd–Ofelt parameters was compared with the experimental lifetime to estimate the quantum efficiency of ⁵D₀ level of Eu³⁺ ions in Li–K–Zn fluorotellurite glass.     

Growth,optical and electro-optical characterisations of potassium hydrogen phthalate crystals doped with Fe3+ and Cr3+ ions

Potassium hydrogen crystals have good electro-optic properties that are in order of urea crystal. Trivalent ions doped KAP crystals KAP:M⁺³ (M = Fe³⁺, Cr³⁺) ions were grown using solution growth technique. Optical and electro-optical characterisations on the coefficient r₅₁ were carried out. The refractive matching offered by the KAP:M⁺³ crystals was investigated. One of the factors causing the observed enhancement in the electro-optics properties is the ligand interactions due the presence of trivalent ions in KAP lattice.     

Optical investigations on Tb3+ doped l-Histidine hydrochloride mono hydrate single crystals grown by low temperature solution techniques

The potential nonlinear optical material of Terbium (Tb³⁺) ion doped l-Histidine hydrochloride monohydrate (LHHC) single crystals were successfully grown. Tb³⁺:LHHC crystals of 7 mm × 5 mm × 3 mm and 59 mm length and 15 mm diameter have been grown by the slow solvent evaporation and Sankaranarayanan-Ramasamy (SR) techniques respectively. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystalline structure and morphology. High resolution X-ray diffraction (HRXRD) studies revealed that the SR grown sample shows relatively good crystalline nature with 9″ full-width at half-maximum (FWHM) for the diffraction curve. Functional groups were identified by Fourier transform infra-red spectroscopy (FTIR). The optical transparency and band gaps of grown crystals were measured by UV–Vis spectroscopy. Thermogravimetric and differential thermal analysis (TG/DTA) studies reveal that the crystal was thermally stable up to 155 °C in SR grown crystal. Surface morphology of the growth plane was observed using scanning electron microscopy (SEM). The incorporation of Tb ion was estimated by EDAX. The frequency-dependent dielectric properties of the crystals were carried out for different temperatures. Vickers hardness study carried out on (1 0 0) face at room temperature shows increased hardness of the SR method grown crystal. Second harmonic generation efficiency of SEST and SR grown crystals are 3.2 and 3.5 times greater than that of pure KDP. The Photoluminescence (PL) studies of Tb³⁺ ions result from the radiative intra-configurational f-f transitions that occur from the ⁵D₄ excited state to the ⁷F_j (j = 6, 5, 4, 3) ground states. The decay curve of the ⁵D₄ level of emission was observed with a long life time of 319.2041 μs for the SR grown Tb³⁺:LHHC crystal.     

Photoluminescence properties of Eu2+-activated Ca2Y2Si2O9 phosphor

Eu²⁺-activated Ca₂Y₂Si₂O₉ phosphors with different Eu²⁺ concentrations have been prepared by a solid-state reaction method at high temperature and their photoluminescence (PL) properties were investigated. Photoluminescence results show that Eu²⁺-doped Ca₂Y₂Si₂O₉ can be efficiently excited by UV–visible light from 300 to 425 nm. Ca₂Y₂Si₂O₉: Eu²⁺ exhibits broad band emission in the wavelength range of 425–700 nm, due to the 4f⁶5d¹ → 4f⁷5d⁰ transition of the Eu²⁺ ions located at two different sites ((Ca/Y)1 and (Ca/Y)2) in Ca₂Y₂Si₂O₉. The effect of the Eu²⁺ concentration in Ca₂Y₂Si₂O₉ on the PL properties was investigated in detail. The results showed that the relative PL intensity reaches a maximum at 1 mol% of Eu²⁺, and a red-shift of the emission bands from these two different sites was observed with increasing Eu²⁺ concentration. Also there exists energy transfer between these two Eu²⁺ sites. The potential applications of Ca₂Y₂Si₂O₉: Eu²⁺ have been pointed out.     

Luminescent properties of vanadium-doped SnO2 nanoparticles

This paper reports the influence of doping degree and annealing temperature on XRD, Raman, EPR and PL spectra of Sn_1−xV_xO₂ nanoparticles with x = 0, 0.01 and 0.05 annealed at 600 and 800 °C. XRD studies reveal a tetragonal rutile crystalline phases of tin oxide, while the formation of V₂O₅ secondary phase was evidenced for all doped nanoparticles only by Raman scattering. In function of the doping degree and annealing temperature, from EPR spectroscopy was evidenced the presence of three different positions for V⁴⁺ ions in the samples: isolated ions disposed on the nanoparticles surface, ions which are coupled by dipolar or exchange interactions and cluster ions. The luminescence emissions associated with oxygen vacancies and structural defects are influenced by doping degree and annealing temperature and could be correlated with the crystallite size determined from XRD patterns.     

Structure and luminescence properties of Ba3WO6:Eu3+ nanowire phosphors obtained by conventional solid-state reaction method

For the first time, novel Ba_3−xWO₆:xEu³⁺ (x = 0.01, 0.03, 0.05, 0.08, 0.1) nanowire phosphors were synthesized by the conventional solid state method. The X-ray pattern indicates that Ba₃WO₆ belongs to the cubic system with space group Fm-3m. The photoluminescence (PL) spectra demonstrate that the phosphors emit strong red light centered at 595 nm corresponding to ⁵D₀ → ⁷F₁ transition of Eu³⁺ ion under CT band excitation. The position of charge transfer (CT) band of Ba_2.95WO₆:0.05Eu³⁺ shifts to a lower energy region (red shift) with the increase of annealing temperature. The co-doped effect of alkali-metal ions (Li⁺, Na⁺, and K⁺) on the luminescence behavior of Ba₃WO₆:Eu³⁺ has been discussed in this paper. The luminescence properties suggest that the Ba₃WO₆:Eu³⁺ phosphor may be a promising candidate in solid-state lighting applications.     

Polyvinylpyrrolidone (PVP)-assisted hydrothermal synthesis of luminescent YVO4:Eu3+ microspheres

Spherical YVO₄:Eu³⁺ microstructures were hydrothermally synthesized by the reaction of NH₄VO₃, Y₂O₃, and Eu₂O₃ at 180 °C for 24 h with the assistance of polyvinylpyrrolidone (PVP) as a surfactant. The resulting products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The experimental results showed that ball-like YVO₄:Eu³⁺ microspheres with a diameter of about 4–5 μm, corresponding to the SEM observations, formed at 180 °C for 24 h using 0.2 g PVP with the molecular weight of 20,000 g mol^?1. The amount of PVP and the reaction time of hydrothermal processing were found to play a key role in the formation of YVO₄:Eu³⁺ microspheres. It has been observed that the relative luminescence intensities of the as-synthesized samples increased with increasing hydrothermal reaction times due mainly to the increase of crystallinity.     

Synthesis and photoluminescence of Y,Eu co-doped ZnO red phosphor

A red emitting ZnO·Y₂O₃:Eu phosphor has been prepared using pyrolysis technique at temperatures ≤1000 °C. When NH₄Cl was used as an ingredient, its luminescence efficiency was quite high indicating that Cl^? ions act as charge compensators since the introduction of Y³⁺ and Eu³⁺ cations in ZnO lattice demands the introduction of equal amount of excess anions. However, Na⁺ or Li⁺ quenches the luminescence efficiency of ZnO·Y₂O₃:Eu. Due to ZnO host absorption, the excitation peaks of ZnO·Y₂O₃:Eu phosphor near 260 nm and 394 nm are suppressed while the one at 468 nm is intense. This red emitting phosphor may find applications when monochromatic excitation such as lasers are involved. XRD data of (Zn_0.93Y_0.07)O_z:Eu³⁺,Cl^? shows the presence of the ZnO phase as well as the Y₂O₃ phase. It shows that Y₂O₃ forms a sublattice within ZnO host. This is supported by the PL data of (Zn_0.93Y_0.07)O_z:Eu³⁺,Cl^? which showed no significant change in the PL efficiency with increase in ZnO molar concentration.     

Crystal growth and scintillation properties of potassium strontium bromide

In this work, potassium strontium bromide activated with divalent europium, (KSr₂Br₅:Eu) has been studied. It has a monoclinic crystal structure and a density of 3.98 g/cm³. Two single crystals of KSr₂Br₅ doped with 5% Eu²⁺, with diameters of 13 mm and 22 mm, were grown in a two zone transparent furnace via the Bridgman technique. The X-ray excited emission spectrum consisted of a single peak at ∼427 nm due to the 5d–4f transition in Eu²⁺. The measured light yield and energy resolution at 662 keV was 75,000 ph/MeV and 3.5%. At low energies KSr₂Br₅:Eu 5% also displays good energy resolution, 6.7% at 122 keV and 7.9% at 59.5 keV.