Synthesis and luminescent properties of SrZnO2:Eu3+,M+ (M = Li,Na, K) phosphor

In this paper, a series of novel luminescent materials, SrZnO₂:Eu³⁺,M⁺ (M = Li, Na, K) have been synthesized by conventional solid-state reaction. X-ray diffraction (XRD) patterns and photoluminescence (PL) spectra were carried out to characterize their structural and luminescent properties. It was found that under ultraviolet excitation with a wavelength of 301 nm, SrZnO₂:Eu³⁺ gives a red luminescence that was attributed to the transitions from ⁵D₀ excited states to ⁷F_J (J = 0–4) ground states of Eu³⁺ ions. The feature and the high intensity of hypersensitive transition ⁵D₀ → ⁷F₂ indicate that Eu³⁺ prefers to occupy a low symmetry site. The incorporation of alkali metal ions greatly enhanced the luminescence intensity and slightly changed the excitation and emission peak position, probably due to the influence of the coordination conditions for Eu³⁺ ions.     

Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4:Eu3+

It has been found that charge compensated CaMoO₄:Eu³⁺ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO₄:Eu³⁺ without charge compensation. Two approaches to charge compensation, (a) 2Ca²⁺ → Eu³⁺ + M⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ acting as a charge compensator; (b) 3Ca²⁺ → 2Eu³⁺ + vacancy, are investigated. The influence of sintering temperature and Eu³⁺ concentration on the luminescent property of phosphor samples is also discussed.     

Li doping effects on the upconversion luminescence of Yb3+/Er3+-doped ABO4 (A = Ca,Sr; B = W,Mo) phosphors

ABO₄ (A = Ca, Sr; B = W, Mo):Er³⁺/Yb³⁺/Li⁺ phosphors tri-doped with different concentrations of Li⁺ ion ranging from 0 to 22.5 mol% were prepared by using a solid-state reaction method. And their upconversion (UC) luminescence properties were in estimated under a 975 nm laser-diode excitation. The four kinds of phosphors (CaWO₄, CaMoO₄, SrWO₄, and SrMoO₄) tri-doped with Er³⁺, Yb³⁺ and Li⁺ ions showed strong green UC emission peaks at 530 nm and 550 nm and weak red UC emission. The intensity of green UC emission of Li⁺ doped samples was several higher than that of Li⁺ un-doped samples due to the reduction of lattice constant and the local crystal field distortion around rare-earth ions. The optimum doping concentration of Li⁺ ions was investigated and the effects of Li⁺ concentration for UC emission intensity were studied in detail.     

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.     

Photoluminescence properties of Y0.95 − xMxBO3:Eu3+ (M = Ca,Sr, Ba,Zn, Al, 0 ≤ x ≤ 0.1) in 100–450 nm regions

The single phases of Y_0.95 − xM_xBO₃:5%Eu³⁺ (M = Ca, Sr, Ba, Zn, Al, 0 ≤ x ≤ 0.1) were synthesized successfully by solid-state reaction. Their luminescent properties were studied under UV and VUV excitation. The results indicated that with the incorporation of Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺ or Al³⁺ into the host lattice of YBO₃:Eu³⁺, the high symmetry around Eu³⁺ was destroyed and the ratio of red emission(⁵D₀–⁷F₂) to orange one (⁵D₀–⁷F₁) increased, leading to a better chromaticity. Furthermore, the co-doping ions such as Ca²⁺, Zn²⁺ and Al³⁺ were beneficial to enhance the luminescent intensity of Eu³⁺. These phenomena were evaluated, and possible explanations were proposed.     

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.     

EPR,optical absorption and luminescence studies of Cr3+-doped antimony phosphate glasses

Antimony phosphate glasses (SbPO) doped with 3 and 6 mol% of Cr³⁺ were studied by Electron Paramagnetic Resonance (EPR), UV–VIS optical absorption and luminescence spectroscopy. The EPR spectra of Cr³⁺-doped glasses showed two principal resonance signals with effective g values at g = 5.11 and g = 1.97. UV–VIS optical absorption spectra of SbPO:Cr³⁺ presented four characteristics bands at 457, 641, 675, and 705 nm related to the transitions from ⁴A₂(F) to ⁴T₁(F), ⁴T₂(F), ²T₁(G), and ²E(G), respectively, of Cr³⁺ ions in octahedral symmetry. Optical absorption spectra of SbPO:Cr³⁺ allowed evaluating the crystalline field Dq, Racah parameters (B and C) and Dq/B. The calculated value of Dq/B = 2.48 indicates that Cr³⁺ ions in SbPO glasses are in strong ligand field sites. The optical band gap for SbPO and SbPO:Cr³⁺ were evaluated from the UV optical absorption edges. Luminescence measurements of pure and Cr³⁺-doped glasses excited with 350 nm revealed weak emission bands from 400 to 600 nm due to the ³P₁ → ¹S₀ electronic transition from Sb³⁺ ions. Cr³⁺-doped glasses excited with 415 nm presented Cr³⁺ characteristic luminescence spectra composed by two broad bands, one band centered at 645 nm (²E → ⁴A₂) and another intense band from 700 to 850 nm (⁴T₂ → ⁴A₂).     

Effects of ultraviolet excitation on the spectroscopic properties of Sm3+ and Tb3+ doped aluminophosphate glasses

Li₂O–BaO–Al₂O₃–La₂O₃–P₂O₅ glasses optically activated with rare earth ions with the 4f⁵, and 4f⁸ electronic configuration (Sm³⁺ and Tb³⁺, respectively) were analyzed by Raman spectroscopy, absorption, excitation photoluminescence, decay curves and temperature dependent photoluminescence. The spectroscopic characteristics of the as-prepared and heat treated samples at temperatures below and above T_g were studied as well as their room temperature photometric properties under ultraviolet excitation. All the doped glasses exhibit typical signatures of the lanthanides in their trivalent charge state. For the samarium doped glass heat treated at 250 °C (<T_g) the Sm²⁺ luminescence was also observed. The analysis of the luminescence efficiency was performed in the interval range of 14 K to room temperature, where the integrated intensity of the luminescence was found to decrease for the Sm³⁺ and Tb³⁺ ions in the studied temperature range. Luminescence decay curves were found to be non-exponential for the ⁴G_5/2 → ⁶H_7/2 and ⁵D₃ → ⁷F₄ transitions of the Sm³⁺ and Tb³⁺ ions, respectively. The results strongly suggest the occurrence of energy transfer processes through cross relaxation phenomena, mediated by dipole–dipole interaction in all the studied samples. The decay of the ⁵D₄ → ⁷F₅ emission of the Tb³⁺ ions was found to be single exponential with a time constant of ∼3.1 ms. Based on the spectroscopic characteristics, models for recombination processes are proposed. The room temperature luminance photometric properties with ultraviolet excitation show that the samarium doped glasses have much lower luminance intensity (around 0.3 Cd/m²) when compared with the 6–7 Cd/m² observed for the terbium doped ones.     

Microstructure and photoluminescent properties of BaY2ZnO5:Tb3+ phosphors with addition of lithium carbonate

In this paper, Tb³⁺ activated BaY₂ZnO₅ phosphors with addition of lithium carbonates (0, 0.0125, 0.025, 0.05, 0.1, and 0.2 molar ratio) were synthesized using the solid-state reaction, and the morphology and photoluminescent properties are investigated. When BaY₂ZnO₅:Tb³⁺ phosphors to which lithium carbonates were added were sintered at 1250 °C for 12 h, X-ray powder diffraction analysis showed that the un-reacted Y₂O₃ raw material decreased and scanning electron microscopy showed that the grain growth is improved. From PL studies, the photoluminescent properties were decreased when Li⁺ ion was added, which might be resulted from the increase of the oxygen vacancy in BaY₂ZnO₅:Tb³⁺ phosphors. The green emission of the BaY₂ZnO₅:Tb³⁺, Li⁺ phosphors showed the CIE chromaticity coordinates in the range of x = 0.3361–0.3510 and y = 0.5202–0.5492.     

Luminescence properties of ZnMoO4:Tb3+ green phosphor prepared via co-precipitation

Tb³⁺-doped ZnMoO₄ green phosphor was synthesized by a co-precipitation method. The morphology and structure of the phosphor were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photoluminescence (PL) spectra were also used to characterize the ZnMoO₄:Tb³⁺ samples. The results show that ZnMoO₄:Tb³⁺ phosphor has triclinic structure with diameters ranging from 1.0 to 2.0 μm. The obtained ZnMoO₄:Tb³⁺ phosphor emits green light emission centered at 541 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ when excited by 378 nm or 488 nm. The optimized concentration of Tb³⁺ is 15 mol.% for the highest emission intensity at 541 nm, and the concentration quenching occurs when the Tb³⁺ concentration is beyond 15 mol.%. The concentration quenching mechanism can be interpreted by the quadrupole–quadrupole interaction of Tb³⁺ ions. The present work suggests a convenient, cost-effective method for green phosphor, which may lead to potential applications in white light-emitting diodes (WLED).     

Lithium solubility limit in ZnGa2O4:Bi0.0013+,Li+ phosphor

The lithium solubility limit, photoluminescence (PL) and photoluminescence excitation (PLE) properties of lithium ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor have been investigated. A LiGaO₂ second phase began to appear from 3 mol% Li⁺ ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor. The enhanced brightness of blue (λ_ex = 254 nm) and white (λ_ex = 315 nm) colors of bismuth ions doped ZnGa₂O₄:Bi³⁺,Li⁺ phosphor was assigned to the formation of LiGaO₂. Bi³⁺ activated lithium zinc gallate phosphor showed a more enhanced PLE peak around 315 nm than that of lithium zinc gallate phosphor when λ_em = 520 nm. Thus, we observed that the PL intensity of ZnGa₂O₄:Bi³⁺,Li⁺ phosphor with λ_em = 520 nm was much greater than that of ZnGa₂O₄:Li⁺ phosphor. Also, ZnGa₂O₄:Bi³⁺,Li⁺ phosphor exhibited a shorter decay time than that of ZnGa₂O₄:Li⁺ phosphor by about a factor of about 2.     

Fluorescence spectroscopy of Er3+:LaOBr prepared by NH4Br solid state reaction

The steady luminescent materials La_1−xEr_xOBr (x = 0, 0.0003, 0.01) were synthesized by a new NH₄Br solid state reaction, and the structures were studied using XRD and Raman methods. Under 514.5 nm Ar⁺ laser excitation, the upconversion fluorescence spectra in LaOBr:Er³⁺ were recorded and investigated. It was found that four upconverted emission bands with peaks at 388 nm, 399 nm, 405 nm (violet) and 477 nm (blue) were observed. All these upconverted emissions were assigned, and the upconversion mechanism was deduced to be excited state absorption (ESA), by analyzing the energy level structures of Er³⁺ ions and measuring the power dependence of upconverted emission intensities.     

Preparation and luminescence characterization of GGAG:Ce3+,B3+ for a white light-emitting diode

We prepared Gd₃Ga₂Al₃O₁₂ (GGAG) co-doped with trivalent cerium and boron ions and investigated its luminescence properties as a function of the B³⁺ concentration. The luminescence intensity was enhanced markedly by adding B³⁺ as a co-dopant. The non-boron-doped GGAG:Ce³⁺ converted less than 10% of the absorbed blue light into luminescence. As the B³⁺ concentration increased, Q increased and reached a maximum of Q = 21% at 1.5 moles in GGAG:Ce³⁺. White light closer to daylight with good color-rendering index properties was generated with the proper combination of yellow emission from GGAG:Ce³⁺,B³⁺ and blue emission from a GaN chip.     

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.     

Scintillation properties of Pr3+-doped lutetium and yttrium aluminum garnets: Comparison with Ce3+-doped ones

Scintillation properties of Pr³⁺-doped LuAG and YAG crystals were investigated and compared with those of Ce³⁺-doped ones. The highest L.Y.’s were observed with the longest shaping time 10 μs. They can reach up to ～16,000 ph/MeV or ～23,500 ph/MeV for LuAG:Pr and LuAG:Ce, respectively. Energy resolutions (FWHM) are a bit better with LuAG:Pr than those of LuAG:Ce, e.g. at 662 keV FWHM are around 6% and between 8–12%, respectively. There were observed no large changes in proportionality of Pr³⁺- or Ce³⁺-doped LuAG or YAG crystals but the best proportionality has YAP:Ce crystal. Pr³⁺- or Ce³⁺-doped LuAG crystals exhibit slow decay components in the time range 1.5–3.5 μs while those of YAG ones have shorter decay components between 0.3–1.7 μs.     

Crystal growth and spectral properties of pure and Co2+-doped Mg3B2O6 crystal

Novel pure and cobalt-doped magnesium borate crystals (Mg₃B₂O₆) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co²⁺:Mg₃B₂O₆ (MBO) were described. From the absorption peaks for the octahedral Co²⁺ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm⁻¹ and 821.6 cm⁻¹, respectively. The fluorescence lifetime of the transition ⁴T₁(⁴P) → ⁴T₂ centered at 717 nm was measured to be 9.68 ms.     

Preparation and luminescent properties of orange reddish emitting phosphor LaMgAl11O19:Sm3+

An orange reddish emitting phosphor, LaMgAl₁₁O₁₉:Sm³⁺, was synthesized by a high temperature solid-state reaction, and the phase formation, crystal structure and luminescence properties were investigated respectively. The LaMgAl₁₁O₁₉:Sm³⁺ phosphor presents a highly intense orange reddish emission peak under the near ultraviolet excitation at 403 nm, which is corresponds to the ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ ions. It was found that the dipole–dipole interactions mainly results in the concentration quenching in the LaMgAl₁₁O₁₉:Sm³⁺ phosphor with a critical quenching concentration at about 5 mol%. The temperature dependence of luminescence properties was studied from 25 to 200 °C and indicated that LaMgAl₁₁O₁₉:0.05Sm³⁺ phosphors had a relatively higher quenching temperature. The chromatic properties of LaMgAl₁₁O₁₉:0.05Sm³⁺ phosphor have been found to have chromaticity coordinate of (0.578, 0.420). All these properties indicate that the orange reddish emitting LaMgAl₁₁O₁₉:Sm³⁺ phosphor has a potential application in w-LEDs.     

Impact of Nd3+ ions on physical and optical properties of Lithium Magnesium Borate glass

Enhancing the up-conversion efficiency of borate glass via optimized doping of rare earth ions is an ever-ending quest in lasing glass. Neodymium (Nd³⁺) doped Lithium Magnesium Borate (LMB) glasses are prepared using the melt-quenching method. X-ray diffraction (XRD), Fourier transformed infrared (FTIR), UV–Vis–NIR absorption and Photoluminescence (PL) spectroscopic characterizations are made to examine the influence of Nd³⁺ concentration on physical properties and optical properties. Nd³⁺ contents dependent density, molar volume, refractive index, ion concentration, Polaron radius, inter nuclear distance, field strength, energy band gap and oscillator strength are calculated. XRD patterns confirm the amorphous nature of all glasses and the FTIR spectra reveal the presence of BO₃ and BO₄ functional groups. UV–Vis–IR spectra exhibit ten prominent bands centered at 871, 799, 741, 677, 625, 580, 522, 468, 426, 349 nm corresponding to the transitions from the ground state to ⁴F_3/2, (⁴F_5/2 + ²H_9/2), (⁴F_7/2 + ⁴S_3/2), ⁴F_9/2, ²H_11/2, (⁴G_5/2 + ²G_7/2), (²K_13/2 + ⁴G_7/2 + ⁴G_9/2), (²G_9/2 + ²D_3/2 + ²P_3/2), (²P_1/2 + ²D_5/2), (⁴D_3/2 + ⁴D_5/2) excited states, respectively. A hyper-sensitive transition related to (⁴G_5/2 + ²G_7/2) level is evidenced at 580 nm. The room temperature up-conversion emission spectra at 800 nm excitation displays three peaks centered at 660, 610 and 540 nm. Glass with 0.5 mol% of Nd³⁺ showing an emission enhancement by a factor to two is attributed to the energy transfer between Mg²⁺ and Nd³⁺ ions. Our results suggest that these glasses can be nominated for solid state lasers and other photonic devices.     

Ag nanoparticles enhanced near-IR emission from Er3+ ions doped glasses

Vitreous materials containing rare-earth (RE) ions and metallic nanoparticles (NPs) attract considerable interest because the presence of the NPs may lead to an intensification of luminescence. In this work, the characteristics of 1.54 μm luminescence for the Er³⁺ ions doped bismuthate glasses containing Ag NPs were studied under 980 nm excitation. The surface plasmon resonance (SPR) band of Ag NPs appears from 500 to 1500 nm. Transmission electron microscopic (TEM) image reveals that the Ag NPs are dispersed homogeneously with the size from 2 to 7 nm. The strength parameters Ω_t(t = 2, 4, 6), spontaneous emission probability (A), radiative lifetime (τ) and stimulated emission section (σ_em) of Er³⁺ ions were calculated by the Judd–Ofelt theory. When the glass contains 0.2 wt% AgCl, the 1.54 μm fluorescence intensity of Er³⁺ reaches a maximum value, which is 7.2 times higher than that of glass without Ag NPs. The Ag NPs embedded glasses show significantly fluorescence enhancement of Er³⁺ ions by local field enhancement from SPR.     

Microstructure,luminescence and thermal stability properties of NaSrPO4:Tb3+ phosphors with various doping concentrations prepared using conventional solid-state sintering

This paper reports the microstructure, luminescence and thermal stability properties of the NaSr_1−xPO₄:xTb³⁺ powders (x = 0.008, 0.01, 0.02, 0.04 and 0.06) via the conventional solid-state sintering at 1200 °C for 5 h. The X-ray diffraction result verifies all diffraction peaks are pure phase of NaSrPO₄. The luminescence results show that the NaSrPO₄:xTb³⁺ powders mainly excited at 370 nm have a series of the emission-states, related to the typical 4f → 4f intra-configuration forbidden transitions of Tb³⁺, and a major emission peak of around 546 nm. The concentration quenching of the NaSr_1−xPO₄:xTb³⁺ phosphors is appeared at x = 0.02. The decay time values of the NaSr_1−xPO₄:xTb³⁺ phosphors for the ⁵D₄ state of the Tb³⁺ are around 3.30 ms to 3.60 ms. It is also found the chromaticity coordinate of NaSrPO₄:Tb³⁺ phosphor varies with the increase of the concentration of Tb³⁺ ions from blue to green. Moreover, the thermal stability of the NaSrPO₄:xTb³⁺ phosphors is slightly better than that of conventional YAG phosphors.