Luminescence properties of tunable red-green emitting phosphor Ba2Ca(BO3)2:Eu3+, Tb3+

A series of Eu3+ or Tb3+ doped Ba2Ca(BO3)2 phosphors were synthesized by a high temperature solid state method, and the luminescence properties are investigated. Ba2Ca(BO3)2:Tb3+ can show an obvious green emission, and the peak locates at 551 nm, which corresponds to the 5D4→7F5 transition of Tb3+. Ba2Ca(BO3)2:Eu3+ can present the characteristic emission of Eu3+, and the peak locates at 600 nm, which is ascribed to the 5D0→7F2 transition of Eu3+. In order to achieve the emission-tunable phosphors, the Eu3+/Tb3+ co-doped Ba2Ca(BO3)2 are synthesized. When tuning the Eu3+ or Tb3+ concentration, Ba2Ca(BO3)2:Eu3+, Tb3+ can both show the tunable emission, which may be induced by the energy transfer from Tb3+ to Eu3+.     

Optically Functional Zeolites: Evaluation of UV and VUV Stimulated Photoluminescence Properties of Ce3+‐ and Tb3+‐doped Zeolite X

The optical properties of Tb³⁺/Ce³⁺ doped zeolites are elucidated with emphasis on ultraviolet (UV) and vacuum ultraviolet (VUV) excitation and luminescence. Ce³⁺ sensitized Tb³⁺ emission with quantum yields of 85 % may be obtained at 330 nm excitation. Low absorptivity at 254 nm due to low Ce³⁺ concentrations or low Ce³⁺/Tb³⁺ ratios, which are required for the suppression of UV components, restricts their applicability as phosphors for Hg‐based discharges, e.g., in conventional fluorescent lamps. Near band edge excitation at 172 nm revealed an immediate quantum yield of 50 % enabled by a zeolite → Ce³⁺ (5d¹) → Tb³⁺ (4f⁷5d¹) energy transfer channel, which may be exploited for the down‐conversion of the Xe₂ excimer emission.     

A Single-Composition Trichromatic White-Light-Emitting Phosphor Based on Sr<Subscript>8</Subscript>ZnY(PO<Subscript>4</Subscript>)<Subscript>7</Subscript> Coactivated with Ce<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, and Mn<Superscript>2+</Superscript>

Ce³⁺/Tb³⁺/Mn²⁺-codoped Sr₈ZnY(PO₄)₇ (SZYP) white-emitting phosphors have been synthesized via solid-state reaction technology. The overlapping spectra between the excitation bands of Mn²⁺ and Tb³⁺ ions and the emission band of Ce³⁺ suggest that Ce³⁺ → Mn²⁺ and Ce³⁺ → Tb³⁺ energy transfer occurs. The emission hues exhibited by Ce³⁺/Tb³⁺- and Ce³⁺/Mn²⁺-codoped phosphors could be modulated from bluish to greenish region and from bluish to reddish region by simply adjusting the relative content of Ce³⁺/Tb³⁺ and Ce³⁺/Mn²⁺, respectively. SZYP:Ce³⁺,Tb³⁺,Mn²⁺ samples exhibited three dominant bands at 410 nm, 545 nm, and 600 nm, attributable to electronic transitions of Ce³⁺, Tb³⁺, and Mn²⁺ ions, respectively. Thus, color-tunable emission was achieved by accurately modulating the concentrations of Ce³⁺, Tb³⁺, and Mn²⁺ ions. SZYP:0.05Ce³⁺,0.11Mn²⁺,0.11Tb³⁺ was found to be an ideal white-light-emitting phosphor with color coordinates of (0.34, 0.33) and correlated color temperature of about 5144.83 K. The results indicate that Ce³⁺/Tb³⁺/Mn²⁺ -tridoped SZYP phosphors are potential single-component white-emitting candidates for application in ultraviolet- and white-light-emitting diodes.     

The effect of different lattice sites substitution on photoluminescence characteristics of Eu2+/Ce3+ doped M5(ZO4)3X

The empirical formula of Van Uitert is applied to calculating the emission wavelengths of haloapatite and silicon apatite phosphors doped with Eu²⁺/Ce³⁺. The relationship between emission wavelengths and occupied lattice sites of Eu²⁺/Ce³⁺ is discussed in haloapatite crystal. For phosphors of haloapatite and silicon apatite doped with Eu²⁺, the emission bands of the long-wave region are interpreted reasonably. Phosphors Sr₅(PO₄)₂SiO₄ doped with Eu²⁺/Ce³⁺ are synthesized by high temperature solid state reaction under two different atmospheres, the spectral characteristics of Eu²⁺/Ce³⁺ occupying different lattice sites are studied. The luminescent materials Sr₅(PO₄)₂SiO₄ doped with Eu²⁺/Ce³⁺ are promising blue-green phosphors for application in white-LEDs.     

Effect of MoO42− partial substitution on optical enhancement of LaNa(MoO4)2:Dy3+ phosphors for white light emitting diodes

Dy³⁺ doped LaNa(MoO₄)₂ phosphors with different anionic groups (SO₄²⁻, PO₄³⁻ and BO₃³⁻) substitution were prepared through solid state reaction at 1100 °C. X-ray diffraction patterns of the as-prepared phosphors indicate that all samples have the standard LaNa(MoO₄)₂ structure. The photoluminescence spectra consist of a blue emission at 484 nm and a yellow emission at 576 nm, which corresponding to the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ions, respectively. The luminescence intensity of LaNa(MoO₄)_1.9(BO₃)_0.1:Dy³⁺, LaNa(MoO₄)_1.8(PO₄)_0.2:Dy³⁺ and LaNa(MoO₄)_1.9(SO₄)_0.1:Dy³⁺ phosphors are 2.8, 1.8 and 3-fold higher than that of LaNa(MoO₄)₂:Dy³⁺ phosphor, respectively. In addition, the luminescence lifetime values of LaNa(MoO₄)₂:Dy³⁺, LaNa(MoO₄)_2−x(BO₃)_x:Dy³⁺, LaNa(MoO₄)_2−x(PO₄)_x:Dy³⁺, and LaNa(MoO₄)_2−x(SO₄)_x:Dy³⁺ are 0.188, 0.189, 0.186 and 0.183 ms, respectively.     

Luminescence properties of Ca4GdO(BO3)3:Eu in ultraviolet and vacuum ultraviolet regions

The luminescent properties of Ca₄GdO(BO₃)₃:Eu³⁺ were investigated under excitation of UV and VUV light. Separate two broad bands at around 259 and 184 nm were observed in the excitation spectrum of Ca₄GdO(BO₃)₃:Eu³⁺. These peaks were assigned to the charge transfer transition of Eu³⁺-O²⁻ and Gd³⁺-O²⁻, respectively. Owing to the favorable spectral position in their broad intense excitation band, Eu³⁺ ions show a intense emission under 258 nm excitation in Ca₄GdO(BO₃)₃:Eu³⁺. This spectral position was determined by the free oxygen ions O (1). Ca₄GdO(BO₃)₃ doped with Eu³⁺ ion seems to be a preferable candidate as red lamp phosphor. On the other hand, a weak band with a maximum at about 184 nm was observed below 200 nm in the excitation spectrum of Ca₄GdO(BO₃)₃:Eu³⁺. This phosphor do not emit effectively under the 147 nm excitation. This unfavorable profile was also due to the O (1) ions, which played a role to the shifting towards the lower energy sides. The luminescence of Eu³⁺ ions in Ca₄GdO(BO₃)₃ was somewhat different from that observed in the other borates phosphors, but resembled to those observed in the oxide phosphors (e.g. Gd₂O₃, Y₂O₃ and Gd₂SiO₅). Such behavior was recognized by the detailed analysis of crystallographical surroundings around activator.     

The effects of Ce3+ doping on the structural and optical properties of SrS nanoparticles synthesized by solid state diffusion method

A solid state diffusion method (SSDM) is employed to synthesize the nanocrystalline SrS phosphors doped with varying concentrations of Ce³⁺ ions. The surface morphology and structural properties of as prepared phosphors are characterized by various techniques including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction pattern (SAED) and energy dispersive X-ray spectroscopy (EDX). The optical properties are investigated and discussed in terms of absorption spectra, photoluminescence (PL) and thermoluminescence (TL) measurements. The cubical crystal structure and average crystallite size estimated by X-ray diffractograms are found to lie in nano-range is also supported by HRTEM analysis. FESEM is used to describe the surface morphology and confirm the crystallite size of as-prepared nanophosphors. The absorption spectra and corresponding Tauc׳s plots confirm the wide band-gap nature of prepared samples. When excited with 375 nm wavelength of ultraviolet (UV) light at room temperature, the SrS:Ce³⁺ nanophosphors exhibit two emission bands at around 459 (blue region) and 551 nm (green region) originating from the ²T_2g(5d)→²F_5/2(4f) and ²T_2g(5d)→²F_7/2(4f) transitions respectively. The results of thermoluminescence (TL) studies in terms of TL glow curves, corresponding kinetic parameters and dopant concentration dependence of intensity for nanocrystalline SrS:Ce³⁺ phosphor are presented and discussed.     

Ce3+-Gd3+ co-doped high efficiency oxide glasses and transfer efficiency from Gd3+ to Ce3+

The rare earth Ce3+ ion doped SiO2-B2O3-BaO-Gd2O3 system is synthesized by high-temperature melting method. The density, transmission, excitation spectra and scintillating properties of the glasses are investigated. The results indicate that all the samples have good physical and scintillating properties. The emission peak wavelength of all samples is 390 nm under X-ray radiation. Gd3+ ions have a negative impact on scintillating properties when its concentration reaches a certain level. Gd3+ ions sensitize the luminescence of Ce3+ ions, and the ideal concentration is 15 mol% for Gd3+ ions. Also the decay characteristics of Ce3+ and Gd3+ ions are investigated. These samples have potential practical applications in high energy physics.     

Pr3+‐ and Pr3+/Er3+‐Doped Selenide Glasses for Potential 1.6 μm Optical Amplifier Materials

1.6 µm emission originated from Pr³⁺: (³F₃, ³F₄) → ³H₄ transition in Pr³⁺‐ and Pr³⁺/Er³⁺‐doped selenide glasses was investigated under an optical pump of a conventional 1480 nm laser diode. The measured peak wavelength and full‐width at half‐maximum of the fluorescent emission are ~1650 nm and ~120 nm, respectively. A moderate lifetime of the thermally coupled upper manifolds of ~212 ± 10 µs together with a high stimulated emission cross‐section of ~(3 ± 1)×10^??20 cm² promises to be useful for 1.6 µm band fiber‐optic amplifiers that can be pumped with an existing high‐power 1480 nm laser diode. Codoping Er³⁺ enhances the emission intensity by way of a nonradiative Er³+: ⁴I_{13/2 →} Pr³⁺: (³F₃, ³F₄) energy transfer. The Dexter model based on the spectral overlap between donor emission and acceptor absorption describes well the energy transfer from Er³⁺ to Pr³⁺ in these glasses. Also discussed in this paper are major transmission loss mechanisms of a selenide glass optical fiber.     

A Quantum‐Splitting Phosphor Exploiting the Energy Transfer from Anion Excitons to Tb3+ in CaSO4:Tb,Na

Wide‐bandgap materials doped with rare‐earth ions are currently of great interest as new vacuum ultraviolet (VUV) phosphors for lighting and displays. This paper reports the development of a highly sensitive green phosphor, CaSO₄:Tb,Na, which exhibits a quantum efficiency higher than 100 % by exploiting the energy‐transfer mechanism from anion excitons to the activator ions, Tb³⁺. The VUV excitation spectra of CaSO₄:Tb³⁺ with Na⁺ as a charge compensator show two prominent excitation bands at 147 and 216 nm. The former band is attributed to the charge‐transfer excitations within SO₄^2– complexes while the latter was assigned to the 4f⁸ → 4f⁷5d transitions on Tb³⁺. The energy‐transfer mechanism from anion excitons to Tb³⁺ strongly raises the possibility of two‐photon emission via a second‐order down‐conversion under the VUV excitation, which is basically a new approach in the goal of achieving a quantum‐splitting phosphor.     

White light emission from Dy3+-doped LiLuF4 single crystal grown by Bridgman method

Lithium lutetium fluoride （LiLuF4） single crystals doped with different Dy3＋ ion concentrations were grown by Bridgman method. The Judd-Ofelt （J-O） strength parameters （Ω2, Ω4, Ω6） of Dy3＋ in LiLuF4 crystal are calculated according to the measured absorption spectra and the J-O theory, by which the asymmetry of the Dy3＋：LiLuF4 single crystal and the possibility of attaining stimulated emission from 4F9/2 level are analyzed. The capability of the Dy3＋：LiLuF4 crystal in generating white light by simultaneous blue and yellow emissions under excitation with ultra- violet light is produced. The effects of excitation wavelength and doping concentration on chromaticity coordinates and photoluminescence intensity are also investigated. Favorable CIE coordinates, x=0.319 3 and y=0.349 3, can be obtained for Dy3＋ ion in 2.701% molar doping concentration under excitation of 350 nm.     

Energy transfer of Ce3+ → Eu2+ in the CaGa2S4 compound

Photoluminescence of CaGa₂S₄:Eu²⁺, CaGa₂S₄:Ce³⁺, and CaGa₂S₄:(Eu²⁺, Ce³⁺) is shown to be caused by intracenter transitions of Eu²⁺ and Ce³⁺ ions. It is ascertained that an energy transfer with an efficiency of 0.43 takes place from Ce³⁺ to Eu²⁺.     

Synthesis of Hexagonal Yb3+,Er3+‐Doped NaYF4 Nanocrystals at Low Temperature

Nanocrystals of NaYF₄ doped with Yb³⁺ and Er³⁺ are synthesized in oleylamine using Y₂(CO₃)₃, Yb₂(CO₃)₃, Er₂(CO₃)₃, Na₂CO₃, and NH₄F as precursors. In contrast to other starting materials normally used for such syntheses, these precursors react even at room temperature to form hexagonal‐phase (β‐phase) NaYF₄:Er,Yb nanoparticles. Cubic‐phase (α‐phase) NaYF₄:Yb,Er particles are formed only at elevated temperatures (>250 °C). The formation of the cubic phase at high temperatures can be suppressed by replacing pure oleylamine with oleic acid/oleylamine mixtures. Under optimized reaction conditions, particles with an average particle size of about 7 nm are generated in 84% yield. Heat treatment (30 min, 280 °C) of the particles significantly increases the luminescence efficiency. A transparent solution of the heat‐treated, nanometer‐sized phosphor in toluene shows intense visible light emission upon excitation in the near infrared.     

White OLED based on a temperature sensitive Eu3+/Tb3+ β-diketonate complex

A mixed lanthanide β-diketonate complex of molecular formula [Eu_0.45Tb_0.55(btfa)₃(4,4′-bpy)(EtOH)] (btfa^– = 4,4,4–trifluoro–1–phenyl–1,3–butanedionate; 4,4′-bpy = 4,4′-dipyridyl; EtOH = ethanol) was synthesized and its structure was elucidated by single crystal X-ray diffraction. The temperature dependence of the complex emission intensity between 11 and 298 K is illustrated by the Commission Internacionale l’Éclairage (CIE) (x, y) color coordinates change within the orange-red region, from (0.521, 0.443) to (0.658, 0.335). The existence of Tb³⁺-to-Eu³⁺ energy transfer was observed at room temperature and as the complex presents a relatively high emission quantum yield (0.34 ± 0.03) it was doped in a 4,4′-bis(carbazol-9-yl)biphenyl (CBP) organic matrix to be used as emitting layer to fabricate a white organic light-emitting diode (WOLED). Continuous electroluminescence emission was obtained varying the applied bias voltage showing a wide emission band from 400 to 700 nm. The white emission results from a combined action between the Eu³⁺ and Tb³⁺ peaks from the mixed Eu³⁺/Tb³⁺ complex and the other organic layers forming the device. The intensity ratio of the peaks is determined by the layer thickness and by the bias voltage applied to the OLED, allowing us to obtain a color tunable light source.     

Strong Self-Trapped Exciton Emission and Highly Efficient Near-Infrared luminescence in Sb3+-Yb3+ Co-doped Cs2AgInCl6 Double Perovskite

Yb³⁺ doped lead-free double perovskites (DPs) with near-infrared (NIR)-emitting have attracted extensive attention due to their wide application prospects. Unfortunately, they still suffer from weak NIR emission due to undesirable resonance energy transfer between the sensitizers and Yb³⁺ ions. Herein, a new effective NIR-emitting DP is developed by co-doping Sb³⁺ and Yb³⁺ into Cs₂AgInCl₆. Experiments and theoretical calculations reveal that induced by co-doping Sb³⁺ ions, the self-trapped excitation (STE) emission intensity of Cs₂AgInCl₆ is greatly enhanced by 240 times, and the STE emission shifts from 600 nm to 660 nm, which contributes to a larger spectral overlap between STE emission and the absorption of Yb³⁺ ions. As a result, the absolute NIR photoluminescence quantum yield reaches an unprecedented 50% in lead-free DPs via high-efficiency STE sensitization (>30%). The excellent optical performance of Cs₂AgInCl₆: Sb, Yb with high ambient, thermal and light stability makes it suitable for application in night-vision devices. Moreover, an ingenious dual-modal optical information encryption based on the combination of visible and NIR fluorescence printing patterns utilizing Cs₂AgInCl₆: Sb and Cs₂AgInCl₆: Sb, Yb respectively is successfully demonstrated. This study provides inspiration for designing highly efficient NIR-emitting Ln³⁺-doped DPs and illustrates their great potential in versatile optoelectronic applications.     

Effect of B2O3 on the spectroscopic properties in Er3+/Ce3+ co-doped tellurite-niobium glass

The high phonon energy oxide of B2O3 is introduced into the Er3+/Ce3+co-doped tellurite-niobium glasses with composition of TeO2-Nb2O5-ZnO-Na2O.The absorption spectra,1.53 μm band fluorescence spectra,fluorescence lifetime and Raman spectra of Er3+in glass samples are measured together with the calculations of Judd-Ofelt spectroscopic parameter,stimulated emission and absorption cross-sections,which evaluate the effect of B2O3 on the 1.53 μm band spectroscopic properties of Er3+.It is shown that the introduction of an appropriate amount of B2O3 can further improve the 1.53 μm band fluorescence intensity through an enhanced phonon-assisted energy transfer(ET) between Er3+/Ce3+ions.The results indicate that the prepared Er3+/Ce3+co-doped tellurite-niobium glass with an appropriate amount of B2O3 is a potential gain medium for the 1.53 μm bandbroad erbium-doped fiber amplifier(EDFA).     

Spectral properties and energy transfer in Er3+/Yb3+ co-doped LiYF4 crystal

Laser crystals of LiYF4 (LYF) singly doped with Er3+ in 2.0% and co-doped with Er3+/Yb3+ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er3+ singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er3+/Yb3+ co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er3+ singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er3+ singly doped crystal to 23.01 ms for Er3+/Yb3+ co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er3+/Yb3+ co-doped crystals are analyzed, and the possible energy transfer processes from Yb3+ to Er3+ are proposed.     

NIR Mechanoluminescence from Cr3+ Activated Y3Al5O12 with Intense Zero Phonon line

Mechanoluminescence (ML) materials with long-wavelength emission bands are essential for future in vivo bioimaging, non-destructive testing of solids, etc. The lack of a defined mechanism, however, prevents the application of near infrared ML materials above 650 nm in several new fields. Here, the addition of Ga³⁺ ions to Y₃Al₅O₁₂: Cr³⁺ manipulates matrix microstructure evolution, boosting near-infrared (NIR) zero-phonon line (ZPL) stress optical output of the Cr³⁺ ion at 688 nm. The key factor changing the crystal field intensity D_q/B due to the addition of Ga³⁺ ions is what causes the luminescence amplification of ZPL. The ML fabricated by composite polydimethylsiloxane and Y₃Al₄GaO₁₂: Cr³⁺ (YAGG: Cr³⁺) may penetrate chicken feet epidermal tissue and 4 mm pork tissue thanks to the strong NIR ZPL emission of YAGG: Cr³⁺ phosphor. This discovery of enhancing near-infrared ZPL intensity by solid solution provides us with a new technique for optimizing NIR ML materials, as well as a new prospect for NIR ML materials in biological applications.     

Down/Up Conversion in Ln3+‐Doped YF3 Nanocrystals

Nanocrystalline Ln³⁺‐doped YF₃ phosphors have been synthesized via a facile sonochemistry‐assisted hydrothermal route. YF₃ nanoparticles are demonstrated to be a good host material for different lanthanides. Varying the dopants leads to different optical properties. In particular, the feasibility of inducing red, green, and especially blue emission in the Yb³⁺/Er³⁺ co‐doped YF₃ sample by up‐conversion excitation in the near‐infrared region is demonstrated. Such unusually strong 411 nm blue up‐conversion emission has seldom been reported in other Yb³⁺/Er³⁺‐doped systems. The up‐conversion mechanisms have been analyzed.     

Electrospinning Derived One‐Dimensional LaOCl: Ln3+ (Ln = Eu/Sm,Tb, Tm) Nanofibers,Nanotubes and Microbelts with Multicolor‐Tunable Emission Properties

One‐dimensional LaOCl: Ln³⁺ (Ln³⁺ = Eu³⁺/Sm³⁺, Tb³⁺, Tm³⁺) nanofibers, nanotubes, and quasi‐1D microbelts are successfully prepared by a sol–gel/electrospinning process. XRD, FT‐IR, SEM, TEM, as well as photoluminescence (PL) and cathodoluminescecne (CL) spectra are used to characterize the resulting samples. Through a heat treatment process at high temperature, the as‐prepared samples are well‐crystallized with the tetragonal structure of LaOCl. Under ultraviolet radiation and low‐voltage electron beam excitation, the LaOCl: Eu³⁺, LaOCl:Sm³⁺, LaOCl: Tb³⁺, and LaOCl: Tm³⁺ samples give the characteristic transitions of Eu³⁺ (⁵D_{0, 1, 2} → ⁷F_{0, 1, 2, 3, 4}), Sm³⁺ (⁴G_5/2 → ⁶H_{5/2, 7/2, 9/2}), Tb³⁺ (⁵D_{3, 4} → ⁷F_{2, 3, 4, 5, 6}), and Tm³⁺ (¹D₂, ¹G₄ → ³F₄, ³H₆), respectively. Moreover, there exists simultaneous luminescence of Tb³⁺, Tm³⁺, Eu³⁺, or Sm³⁺ individually when codoping them in the single‐phase LaOCl host (for example, LaOCl: Tb³⁺, Eu³⁺/Sm³⁺; LaOCl: Tm³⁺, Eu³⁺/Sm³⁺; LaOCl: Tb³⁺, Tm³⁺, Eu³⁺/Sm³⁺ systems), which is beneficial to tune the emission colors. Under low‐voltage electron beam excitation (1–5 kV), a variety of colors can be efficiently adjusted in a wide triangle region enveloped by three CIE chromaticity coordinate points [LaOCl:Eu³⁺, (x = 0.6039, y = 0.3796); LaOCl: Tb³⁺, (x = 0.2452, y = 0.5236); LaOCl: Tm³⁺, (x = 0.1456, y = 0.0702)] for mono‐ and co‐doped LaOCl: Ln³⁺ (Eu³⁺, Sm³⁺, Tb³⁺, Tm³⁺) samples, making these materials have potential applications in field‐emission display devices.