Luminescence properties of Ba2LiB5O10:Dy phosphor

A novel warm white phosphor Ba₂LiB₅O₁₀:Dy³⁺ with various Dy³⁺ concentrations was synthesized by the conventional solid-state reaction at 800 °C. The crystal structure of the phosphor was characterized by X-ray diffraction (XRD). The photoluminescence properties of Ba₂LiB₅O₁₀:Dy³⁺ were investigated, and the critical concentration of the activator ion (Dy³⁺) was found to be 0.04 mol per formula unit. Under the ultraviolet excitation of 348 nm, the phosphor presented warm white luminescence with dominating emissions at 484.6 and 577 nm, corresponding to ⁴F_9/2-⁶H_15/2, ⁴F_9/2-⁶H_13/2 transitions, respectively. The chromatic properties of the typical sample Ba₂LiB₅O₁₀:0.04Dy³⁺ phosphor have been found to have chromaticity coordinates of x = 0.31 and y = 0.35.     

Conversion of green emission into white light in Gd2O3 nanophosphors

Gd₂O₃ nanophosphors were prepared by combustion synthesis with and without doping of Dy³⁺ ions. The X-ray powder diffraction patterns indicate that as-prepared Gd₂O₃ and 0.1 mol% Dy₂O₃ doped Gd₂O₃ nanophosphors have monoclinic structures. The transmission electron microscope (TEM) studies revealed that the as-prepared phosphors had an average crystallite sizes around 37 nm. The excitation and emission properties have been investigated for Dy³⁺ doped and undoped Gd₂O₃ nanophosphors. New emission bands were observed in the visible region for Gd₂O₃ nanophosphors without any rare earth ion doping under different excitations. A tentative mechanism for the origin of luminescence from Gd₂O₃ host was discussed. Emission properties also measured for 0.1 mol% Dy³⁺ doped Gd₂O₃ nanophosphors and found the characteristic Dy³⁺ visible emissions at 489 and 580 nm due to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. The chromaticity coordinates were calculated based on the emission spectra of Dy³⁺ doped and undoped Gd₂O₃ nanophosphors and analyzed with Commission Internationale de l'Eclairage (CIE) chromaticity diagram. These nanophosphors exhibit green color in undoped Gd₂O₃ and white color after adding 0.1 mol% Dy₂O₃ to Gd₂O₃ nanophosphors under UV excitation. These phosphors could be a promising phosphor for applications in flat panel displays.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Photoluminescence properties of RE-activated Na3GdP2O8 (RE = Tb, Dy, Eu, Sm) under VUV excitation

RE³⁺-activated monoclinic Na₃GdP₂O₈ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na₃GdP₂O₈:RE³⁺ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) were assigned and corroborated. For the sample Na₃GdP₂O₈:5%Tb³⁺, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb³⁺. For Na₃GdP₂O₈:5%Dy³⁺, the broad band at 176 nm could be related to the f-d transitions of Dy³⁺ and the O²⁻ → Dy³⁺ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu³⁺ doped sample, the O²⁻ → Eu³⁺ CTB is observed to be at 245 nm. For the Sm³⁺ doped sample, the O²⁻ → Sm³⁺ CTB is not distinguished obviously and is overlapped with the host-related absorption band.     

Preparation and upconversion property of TeO2:Er/Yb nanoparticles

Different crystal structure of TeO₂ nanoparticles were used as the host materials to prepare the Er³⁺/Yb³⁺ ions co-doped upconversion luminescent materials. The TeO₂ nanoparticles mainly kept the original morphology and phase after having been co-doped the Er³⁺/Yb³⁺ ions. All the as-prepared TeO₂:Er³⁺/Yb³⁺ nanoparticles showed the green emissions (525 nm, 545 nm) and red emission (667 nm) under 980 nm excitation. The green emissions at 525 nm, 545 nm and red emission at 667 nm were attributed to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of the Er³⁺ ions, respectively. For the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, three-photon process involved in the green (²H_11/2 → ⁴I_15/2) emission, while two-photon process involved in the green (⁴S_3/2→⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. For the β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, two-photon process involved in the green (²H_11/2 → ⁴I_15/2), green (⁴S_3/2 → ⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. It suggested that the crystal structure of TeO₂ nanoparticles had an effect on transition processes of the Er³⁺/Yb³⁺ ions. The emission intensities of the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles and β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles were much stronger than those of the (α + β)-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles.     

Infrared to visible upconversion luminescence in Er/Yb co-doped CeO2 inverse opal

Infrared to visible upconversion luminescence has been investigated in Er³⁺/Yb³⁺ co-doped CeO₂ inverse opal. Under the excitation of 980 nm diode lasers, visible emissions centered at 525, 547, 561, 660 and 680 nm are observed, which are assigned to the Er³⁺ transitions of ²H_11/2 → ⁴I_15/2 (525 nm), ⁴S_3/2 → ⁴I_15/2 (547, 561 nm), ⁴F_9/2 → ⁴I_15/2 (660 and 680 nm), respectively. The effect of photonic band gap on the upconversion luminescence intensity was also obtained. Additionally, the upconversion luminescence mechanism was studied. The dependence of Er³⁺ upconversion emission intensity on pump power reveals that it is a two-photon excitation process.     

Observation of broadband infrared luminescence in a novel Bi-doped P2O5-B2O3-Al2O3 glass

A novel Bi-doped P₂O₅-B₂O₃-Al₂O₃ glass was investigated, and strong broadband NIR (near infrared) luminescence was observed when the sample was excited by 445 nm, 532 nm, 808 nm and 980 nm lasers, respectively. The max FWHM with 312 nm, the lifetime with 580 μs and the σ_emτ product with 5.3 × 10^− 24 cm² s were obtained which indicates that this glass is a promising material for broadband optical amplifier and tunable laser. The effect of the introduction of B₂O₃ on the glass structure and Bi-ions illuminant mechanism were discussed and analyzed. It is suggested that the introduction of B₂O₃ makes the glass structure closer, and the broadband NIR emission derives from Bi⁰:²D_3/2 → ⁴S_3/2 and Bi⁺:³P₁ → ³P₀ transitions.     

White upconverted luminescence of Ho/Yb/Tm tri-doped Gd2Mo3O9 phosphors

Yb³⁺/Tm³⁺/Ho³⁺ tri-doped Gd₂Mo₃O₉ phosphors were synthesized by the high-temperature solid-state method. Under 980 nm near-infrared excitation, the white-light emission can be observed, which is consists of the blue, green, and red UC emissions. The green and red emission at 547 nm and 660 nm originated from the transition of Ho³⁺ (⁵S₂, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈) and the blue emission at 475 nm attributed to the transition of Tm³⁺ (⁵G₄ → ⁵H₆). In this experiment, we selected the optimum concentration ratio of the three rare earths for the bright white emission. The Commission internationale de L’Eclairage (CIE) coordinates for the samples were calculated, and chromaticity coordinates were very close to white light regions. We find that the calculated CIE color coordinates of the Yb³⁺/Tm³⁺/Ho³⁺ tri-doped Gd₂Mo₃O₉ phosphors changed with the incident pump power from 400 mW/cm² to 1000 mW/cm². The upconversion luminescence mechanism of the samples was discussed on its spectral. The white light may be proved to be a candidate material for applications in various fields.     

Synthesis and luminescent characteristic of Eu-doped (Gd,Lu)2O3 nanopowders

Eu³⁺ doped (Gd,Lu)₂O₃ nanopowders with particle sizes ranging from 20 to 70 nm were synthesized by the co-precipitant method using mixed precipitants, namely the mixture of ammonium hydroxide (NH₃⋅H₂O) and ammonium hydrogen carbonate (NH₄HCO₃). The precipitate precursor prepared by this method was believed to possess a basic carbonate composition and its thermal decomposition of the (Gd,Lu)₂O₃:Eu³⁺ powders were investigated by Thermogravimetric analysis and differential thermal analysis (TG-DTA). This preparation was followed by a calcination process at 800-1100 °C and corresponding phosphor structure were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence measurement of the (Gd,Lu)₂O₃:Eu³⁺ particles show typical red emission at the 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition. We found that the optimal Eu³⁺ molar doping concentration, calcined temperature and reaction time were 7 mol%, 1000 °C, and 2 h, respectively, which is helpful to obtain the final transparent ceramics with excellent properties.     

Preparation and second harmonic generation of Ba2TiSi2O8 films

The synthesis and characterization of the Ba₂TiSi₂O₈ films are described. The Ba₂TiSi₂O₈ crystal was obtained after heat treatment at above 630 °C of a sol-gel derived glassy material which has a chemical composition (mole ratio) 2BaO, TiO₂, 2SiO₂, and then the Ba₂TiSi₂O₈ films were formed from the hydration of CaO-P₂O₅ glass powders. Heat treatment conditions and crystallization of the synthesized materials were studied by DSC-TG, XRD, and FT-IR. Second order nonlinear optical property has been verified by second harmonic generation test at 1064 nm. These results showed that the hydration process has a potential in rendering shape-comfortable optical materials.     

Tuning the luminescence color and enhancement of afterglow properties of Sr(4−x−y)CaxBayAl14O25:Eu,Dy phosphor by adjusting the composition

Color point tuning is an important challenge for improving the practical applications of various displays, especially there are very limited white color single hosts that emits in the white spectrum. In this paper, the possibility of color tuning by substituting part of host lattice cation (Sr²⁺ ions) by Ca²⁺ or Ba²⁺ ions in an efficient strontium aluminate phosphor, Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺, is reported and found to be very promising for displays. A detail study by replacing part of Sr²⁺ with Ca²⁺ or Ba²⁺ has been investigated. X-ray diffraction study showed that crystal structure of Sr₄Al₁₄O₂₅ is preserved up to 20 mol of Ca²⁺ ion exchange while it is limited to 10 mol of Ba²⁺ ions exchange. Substantial shift in the emission band and color were observed by substitution of Sr²⁺ by Ca²⁺ or Ba²⁺ ions. A bluish-white emission and afterglow was observed at higher Ca²⁺ ions substitution. Further, partial Ca²⁺ substitutions (up to 0.8 mol) resulted in enhanced afterglow of Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor. However, Ba²⁺ substitution decreased the fluorescence as well afterglow of the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor significantly. The enhanced phosphorescence by partial Ca²⁺ substitution is explained on the basis of increased density of shallow traps associated with higher solubility of Dy³⁺ ions in to the host lattice due to equivalent size of Ca²⁺ and Dy³⁺ ions. Thus, Ca²⁺ substitution in the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor is a promising method for tuning the emission color and improving the afterglow intensity of the phosphor.     

Intense yellow emission in Dy-doped LiGd(MoO4)2 crystal for visible lasers

The spectroscopic properties of Dy³⁺:LiGd(MoO₄)₂ crystal have been investigated with aim to assess the feasibility of laser operation in the yellow region. On the basis of the analysis of polarized absorption spectra in the framework of the Judd-Ofelt theory, the main spectroscopic characteristics relevant for laser applications have been determined. An intense yellow emission band corresponding to the ⁴F_9/2 → ⁶H_13/2 transition around 575 nm has been observed in the visible region. The emission cross-sections for the ⁴F_9/2 → ⁶H_13/2 transition have been calculated using the Füchtbauer-Ladenburg formula. The fluorescence and radiative lifetimes of the ⁴F_9/2 manifold are equal to 139.0 μs and 199.1 μs, respectively, and the quantum efficiency is 69.8%.     

High pressure luminescence and time resolved spectra of La2Be2O5:Pr

We present luminescence, luminescence excitation and luminescence time resolved spectra of La₂Be₂O₅:Pr³⁺ system. We used high pressure spectroscopy approaches, with high pressure applied in diamond anvil cell (DAC) and sapphire anvil cell (SAC), for detailed analysis of luminescence related to the 4f5d → 4f² and 4f² → 4f² transitions. We present effect of up-converted luminescence related to 4f5d → 4f² transition excited with 488 nm. We also discussed possibility of existence of praseodymium trapped exciton (PTE) states in La₂Be₂O₅:Pr³⁺ system. Lack of the PTE is attributed to high quantity of bulk modulus of this material.     

A reddish La2O2S-based long-afterglow phosphor with effective absorption in the visible light region

Sm³⁺-activated La₂O₂S phosphors with good crystallinity were prepared by solid-state reaction. The formation mechanism of La₂O₂S formation was assumed and the phase change with different temperatures was discussed. The luminescence properties of phosphors with different sintering temperatures and different doping concentrations of Sm³⁺were investigated. The emission peak at 605 nm showed a well intensity can be attributed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The optical absorption of La₂O₂S phosphors showed a stronger intensity in UV-vis region comparing with the Y₂O₂S phosphors. The long afterglow properties were investigated after the phosphors were excited with a fluorescent lamp. Phosphorescence lasted for about 3 min in the limit of light perception of the dark-adapted human eye (0.32 mcdm⁻²).     

Transparent glass ceramic containing Er:CaF2 nano-crystals prepared by sol-gel method

Er³⁺ doped SiO₂-CaF₂ transparent glass ceramic was prepared by sol-gel method. The microstructural evolution of the samples was studied with X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared spectra (IR). After heat-treatment at 900 °C, the Si-OH bonds and other organic groups were basically eliminated. The CaF₂ crystallites in the sample heat-treated at 900 °C are 10-20 nm in size, distributed homogeneously among the amorphous silica matrix. The efficient upconversion emission for Er^3+.4F_9/2 → ⁴I_15/2 transition was recorded under 980 nm excitation, which could be ascribed to the incorporation of Er³⁺ ions into the CaF₂ nano-crystals with low phonon energy.     

Intensity parameters of Tm doped Sc2O3 transparent ceramic laser material

This work is focused on spectral investigations of Tm³⁺ doped Sc₂O₃ transparent ceramic as potential material for diode-pumped solid-state laser emitting around 2 μm. In the context of the Judd-Ofelt (J-O) theory a series of spectroscopic parameters such as J-O intensity parameters, oscillator strengths, radiative transitions probabilities, and radiative lifetimes as well as branching ratios are evaluated. The gain cross-sections which lead to an estimation of the probable operating laser wavelength for the ³F₄ → ³H₆ Tm³⁺ laser transition were also calculated.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Preparation of SrAl2O4: Eu, Dy nanometer phosphors by detonation method

SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer phosphors were synthesized by detonation method. The particle morphology and optical properties of detonation soot that was heated at different temperatures (600–1100 °C) had been studied systematically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer powders in monoclinic system (a = 8.442, b = 8.822, c = 5.160, β = 93.415) can be synthesized by detonation method, when detonation soot was heated at 600–800 °C. The particle size of SrAl₂O₄: Eu²⁺, Dy³⁺ is 35 ± 15 nm. Compared with the solid-state reaction and sol-gel method, synthesis temperature of the detonation method is lower about 500 and 200 °C respectively. After being excited under UN lights, detonation soot and that heated at 600–1100 °C can emit a green light.     

Synthesis and blue to near-infrared quantum cutting of Pr/Yb co-doped Li2TeO4 phosphors

Near-infrared (NIR) quantum cutting luminescent materials Li₂TeO₄ doped with Pr³⁺ and Yb³⁺ were synthesized by solid-state reaction method. The dependence of Yb³⁺ doping concentration on the visible- and NIR-emissions, decay lifetime, and quantum efficiencies of the phosphors are investigated. Quantum cutting down-conversion involving 647 nm red emission and 960-1050 nm broadband near-infrared emission for each 487 nm blue photon absorbed is realized successfully in the resulting phosphors, of which the process of near-infrared quantum cutting could be expressed as ³P₀(Pr³⁺) → ²F_5/2(Yb³⁺) + ²F_5/2(Yb³⁺). The maximum quantum cutting efficiency approaches up to 166.4% in Li₂TeO₄: 0.3 mol%Pr³⁺, 1.8 mol%Yb³⁺ sample corresponding to the 66.4% value of energy transfer efficiency.     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.