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.     

Fluorosilicate and fluorophosphate superfluorescent multicore optical fibers co-doped with Nd3+/Yb3+

In the paper spectroscopic properties of two fluorosilicate and fluorophosphate glass systems co-doped with Nd³⁺/Yb³⁺ ions are investigated. As a result of optical excitation at the wavelength of 808 nm strong and wide emission in the 1 μm region corresponding to the superposition of optical transitions ⁴F_3/2 → ⁴I_11/2 (Nd³⁺) and ²F_5/2 → ²F_7/2 (Yb³⁺) can be observed. The optimization of Nd³⁺ → Yb³⁺ energy transfer in both glasses allows to manufacture multicore optical fibers with narrowing and red-shifting of amplified spontaneous emission (ASE) at 1.1 μm.     

Er3+–Tm3+ co-doped tellurite fibers for broadband optical fiber amplifier around 1550 nm band

Tellurite fibers with 7500 ppm Er³⁺ concentration and diverse 2500–15,000 ppm Tm³⁺ concentrations were manufactured, and their amplified spontaneous emission (ASE) intensities 1550 nm band around were obtained for 980 and 790 nm pump laser. Maxima 187 nm bandwidth at −3 dB points using Er³⁺–Tm³⁺ co-doped tellurite optical fibers pumping at 790 nm was obtained, and energy transfer (ET) process between ⁴I_13/2 Er³⁺ and ³F₄ Tm³⁺ levels related with the amplifier quantum efficiency was studied from experimental and calculated lifetime.     

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.     

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.     

Preparation and Photoluminescence Properties of Pr3+ Ion-Doped Ca2LaTaO6 Phosphors

In this study, Pr³⁺ ion-doped Ca₂LaTaO₆ phosphors were synthesized using a vibrating milled solid-state reaction with metal oxides and calcined in air at 1100°C for 8 h. The crystal structure and photoluminescence properties were also investigated. The x-ray powder diffraction patterns show that all of the peaks can be attributed to monoclinic Ca₂LaTaO₆ phase with increasing Pr³⁺ ion doping. The scanning electron microscopy images show that the particles are irregular, with the most uniform distribution being obtained for Pr³⁺ ion concentration of 3 mol.%. The emission spectra of Ca₂(La_1?x Pr _x )TaO₆ phosphors showed a dominant green emission peak at 490 nm under excitation at 451 nm, which was due to the ³P₀ → ³H₄ transition. A series of weak emission peaks at 531 nm, 544 nm, 615 nm, 621 nm, and 652 nm were assigned to the ³P₀ → ³H₅, ¹D₂ → ³H₄, ³P₀ → ³H₆, and ³P₀ → ³F₂ transitions of Pr³⁺ ions, respectively. In addition, the emission intensities of the Ca₂(La_1?x Pr _x )TaO₆ phosphors increased then decreased as the Pr³⁺ ion concentration was increased, and the maximum emission intensity occurred for x of 0.03, corresponding to an average grain size of 41.5 nm with critical distance of 16.32 Å. The Commission Internationale de l’Eclairage color chromaticity coordinates for the Ca₂LaTaO₆:Pr³⁺ phosphors were all located in the green region, but shifted from (x = 0.145, y = 0.463) to (x = 0.119, y = 0.471) as the Pr³⁺ ion concentration was increased from 0.5 mol.% to 10 mol.%.     

Effects of Phonon Confinement on Anomalous Thermalization,Energy Transfer,and Upconversion in Ln3+‐Doped Gd2O3 Nanotubes

There is a growing interest in understanding how size‐dependent quantum confinement affects the photoluminescence efficiency, excited‐state dynamics, energy‐transfer and thermalization phenomena in nanophosphors. For lanthanide (Ln³⁺)‐doped nanocrystals, despite the localized 4f states, confinement effects are induced mostly via electron–phonon interactions. In particular, the anomalous thermalization reported so far for a handful of Ln³⁺‐doped nanocrystals has been rationalized by the absence of low‐frequency phonon modes. This nanoconfinement may further impact on the Ln³⁺ luminescence dynamics, such as phonon‐assisted energy transfer or upconversion processes. Here, intriguing and unprecedented anomalous thermalization in Gd₂O₃:Eu³⁺ and Gd₂O₃:Yb³⁺,Er³⁺ nanotubes, exhibiting up to one order of magnitude larger than previously reported for similar materials, is reported. This anomalous thermalization induces unexpected energy transfer from Eu³⁺ C₂ to S₆ crystallographic sites, at 11 K, and ²H_11/2 → ⁴I_15/2 Er³⁺ upconversion emission; it is interpreted on the basis of the discretization of the phonon density of states, easily tuned by varying the annealing temperature (923–1123 K) in the synthesis procedure, and/or the Ln³⁺ concentration (0.16–6.60%).     

Hydrothermal Synthesis of SrMoO4:Eu3+, Sm3+ Phosphors and Their Enhanced Luminescent Properties Through Energy Transfer

Eu³⁺ and Sm³⁺ co-doped SrMoO₄ phosphors have been successfully prepared via a simple surfactant-free hydrothermal method. The as-prepared phosphors present dumbbell-like agglomerates and comprise of many nanoparticles of 150–300 nm in diameter. Eu³⁺ and Sm³⁺ co-doped SrMoO₄ phosphors display all the characteristic excitations and emissions of Eu³⁺ and Sm³⁺. The introduction of Sm³⁺ can generate a strong excitation line at 403 nm, originating from the ⁶H_5/2 → ⁴K_11/2 transition of Sm³⁺, which significantly broadened the excitation region for matching the near ultraviolet light emitting diodes (～400 nm). And Sm³⁺ ions can transfer the absorbed energy to Eu³⁺ ions efficiently, so the intensity of the main emission peak at 614 nm due to ⁵D₀ → ⁷F₂ transition of Eu³⁺ are strengthened by the co-doping of Sm³⁺. The doping concentration of Eu³⁺/Sm³⁺ was optimized. In addition, the possible energy transfer mechanism has been investigated and is discussed in detail.     

Monovalent Charge Compensation Enables Efficient Lanthanide-Based Near-Infrared Perovskite LEDs

Lanthanide ions (Yb³⁺ or Er³⁺) alloying of CsPb(Cl_1-xBr_x)₃ quantum dots (QDs) to emit approaching 1000 nm show promise in near-infrared light-emitting diodes (NIR-LEDs). High Yb³⁺ alloying ratio increases the electroluminance efficiency of emission at 990 nm and enables high external quantum efficiency (EQE) of NIR-LEDs, however, the high alloying ratio also results in inferior material stability and PLQY drop because of Yb³⁺-induced nanocrystal precipitation. This study finds that the heavy alloying of Yb³⁺ ions causes lattice distortion and coherent energy reduction of Yb³⁺: CsPb(Cl_1-xBr_x)₃ QDs, induced by two Yb³⁺ ions replacing three Pb²⁺, which leads to the collapse of the octahedral structure in ambient conditions. It posits that spontaneous monovalent ion (Na⁺) alloying can address the trade-off between material stability and emission intensity. The Na⁺ occupies the vacancy of Pb²⁺ ions, relaxing the distortion in the lattice and improving the phase stability of octahedral structure, and this optimized structure in turn allows a higher Yb³⁺ alloying ratio. Stability measurements show that the Na⁺/Yb³⁺ co-alloyed films show ten-fold higher material stability and 2.0-fold emission efficiency related to controls. It reports that as a result Na⁺/Yb³⁺ co-alloyed NIR-LEDs have an EQE of 6.4% at 990 nm, which is among the highest perovskite NIR-LEDs beyond 950 nm.     

Effect of Yb^3＋ concentration on Er^3＋ luminescence properties of sol-gelderived silica-alumina xerogels

Er~(3 )-activated silicate glasses are recognized of tech-nological interest in several areas and,in particular ,it iswell known for their successful application in opticalamplification at the C band (1530 -1565 nm) of tele-communications[1].Inside this l…     

Improvement of 1.53 μm emission and energy transfer of Yb3+/Er3+ co-doped tellurite glass and fiber

To improve the 1.53 μm band emission of Er³⁺, the trivalent Yb³⁺ ions were introduced into the Er³⁺ single-doped tellurite glass with composition of TeO₂–ZnO–La₂O₃, a potential gain medium for Er³⁺-doped fiber amplifier (EDFA). The improved effects were investigated from the measured 1.53 μm band and visible band spontaneous emission spectra together with the calculated 1.53 μm band stimulated emission (signal gain) spectra under the excitation of 975 nm laser diode (LD). It was found that Yb³⁺/Er³⁺ co-doping scheme can remarkably improve the visible band up-conversion and the 1.53 μm band fluorescence emission intensity, and meanwhile improves the 1.53 μm band signal gain to some extent, which were attributed to the result of the effective energy transfer of Yb³⁺:²F_5/2 + Er³⁺:⁴I_15/2 → Yb³⁺:²F_7/2 + Er³⁺:⁴I_11/2. The quantitative study of energy transfer mechanism was performed and microscopic energy transfer parameters between the doped rare-earth ions were determined. In addition, the spectroscopic properties of Er³⁺ were also investigated from the measured absorption spectrum according to the Judd–Ofelt theory, and the structure behavior and thermal stability of the prepared tellurite glass were analyzed based on the X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurements, respectively.     

Enhanced emission of 2.9 μm from Ho3+/Pr3+ co-doped LiYF4 crystal excited by 640 nm

The use of Pr3+co-doping for great enhancement of mid-infrared(mid-IR) emissions at 2.9 μm and 2.4 μm is investigated in the Ho3+/Pr3+co-doped LiYF4 crystals.With the introduction of Pr3+ions,the fluorescence lifetime of Ho3+:5I7 level is 2.15 ms for Ho3+/Pr3+co-doped crystal,and the lifetime for Ho3+singly doped crystal is 17.70 ms,while the lifetime of Ho3+:5I6 level decreases slightly from 2.11 ms for Ho3+:LiYF4 to 1.83 ms for Ho3+/Pr3+:LiYF4.It is also demonstrated that the introduction of Pr3+greatly increases the mid-infrared emission of Ho3+:5I6 →5I7 which depopulates the Ho3+:5I7 level,while it has little influence on the Ho3+:5I6 level,which is beneficial for greater population inversion and laser operation.The analysis on the decay curves of the 2.0 μm emissions in the framework of the Inokuti-Hirayama model indicates that the energy transfer from Ho3+to Pr3+is mainly from electric dipole-dipole interaction.The calculated efficiency of energy transfer from Ho3+:5I7 to Pr3+:3F2 level is 87.53% for Ho3+/Pr3+(1.02%/0.22%) co-doped sample.Our results suggest that the Ho3+/Pr3+co-doped LiYF4 single crystals may have potential applications in mid-IR lasers.     

Electrospinning Preparation and Drug‐Delivery Properties of an Up‐conversion Luminescent Porous NaYF4:Yb3+, Er3+@Silica Fiber Nanocomposite

Up‐conversion (UC) luminescent porous silica fibers decorated with NaYF₄:Yb³⁺, Er³⁺ nanocrystals (NCs) (denoted as NaYF₄:Yb³⁺, Er³⁺@silica fiber) are prepared by the electrospinning process using cationic surfactant P123 as a template. Monodisperse and hydrophobic oleic acid capped β‐NaYF₄: Yb³⁺, Er³⁺ NCs are prepared by thermal decomposition methodology. Then, these NCs are transferred into aqueous solution by employing cetyltrimethylammonium bromide (CTAB) as secondary surfactant. The water‐dispersible β‐NaYF₄:Yb³⁺, Er³⁺ NCs are dispersed into precursor electrospinning solution containing P123 and tetraethyl orthosilicate (TEOS), followed by preparation of precursor fibers via electrospinning. Finally, porous α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber nanocomposites are obtained after annealing the precursor fibers containing β‐NaYF₄:Yb³⁺, Er³⁺ at 550 °C. The as‐prepared α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber possesses porous structure and UC luminescence properties simultaneously. Furthermore, the obtained nanocomposites can be used as a drug delivery host carrier and drug storage/release properties are investigated, using ibuprofen (IBU) as a model drug. The results indicate that the IBU–loaded α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber nanocomposites show UC emission of Er³⁺ under 980 nm NIR laser excitation and a controlled release property for IBU. Meanwhile, the UC emission intensity of IBU–α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber system varies with the released amount of IBU.     

High power cladding-pumped Er3+/Yb3+ fiber amplifiers: technologies, performances and impact of nonlinear effects

Yb³⁺-sensitized Er³⁺-doped fibers are attracting increasing interest because of the high achievable performances, such as high gain and pump efficiency. High output power can be obtained from a double clad (dc) Er³⁺/Yb³⁺ co-doped fiber pumped with broad area high power pump laser diodes. The principle of amplification in this kind of co-doped fibers is presented in this paper. Different solutions for the injection of pump power in the 1^st-cladding have been described. The energy transfer mechanism in a Er³⁺/Yb³⁺ co-doped system including cooperative-upconversion process is explained. Gain and absorption properties ofdc fibers have been determined experimentally and inserted in a theoretical amplifier model. Good agreement between measurements and modelling has been obtained. Hybrid Er³⁺-Er³⁺/Yb³⁺ amplifier architectures are suitable to obtain + 30 dBm output power. The gain bandwidth is in the 1535–1565 nm range for single wavelength operation. A spectral gain flatness is observed in a reduced C-bandWDM operation (i.e. 1545–1565 nm) without gain-flattening filter. Nonlinear effects such as the optical Kerr effect or the stimulated Brillouin scattering can be observed in high power amplifiers due to the high output peak power confined in the fiber core. These two nonlinear phenomena have been investigated for different high power amplifier configurations. Numerical modelling have also confirmed the observed signal distortions.     

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.     

Broadband near-infrared luminescence and energy transfer in Bi singly-doped and Bi/Yb co-doped titanate glasses

Super-broadband near-infrared(NIR)emission from 1100 nm to 1600 nm is observed in Bi-doped titanate glasses at the excitation of 808 nm laser diode(LD).The effects of Bi content on the optical spectra are investigated.It is also found that the Bi-related emission intensity can be enhanced by Yb3+co-doping at the excitation of 980 nm LD.It should be ascribed to the energy transfer from Yb3+to active Bi ions.The energy transfer processes are studied based on the Inokuti-Hirayama(I-H)model,and the energy transfer of electric dipole-dipole interaction is confirmed to be dominant in Bi/Yb co-doped glasses.     

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+.     

Luminescence properties of light-emitting diodes based on GaAs with the up-conversion Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Er,Yb luminophor

Y₂O₂S luminophors doped with Er³⁺ and Yb³⁺ ions are produced by means of solid-phase synthesis and deposited onto standard AL123A infrared light-emitting diodes. When excited with 940 nm radiation from a light-emitting diode, the structures exhibit intense visible up-conversion luminescence. A maximal brightness of 2340 cd/m² of green and red up-conversion luminescence at corresponding wavelengths around 550 and 600 nm is observed for the Y₂O₂S compound doped with 2 at % Er³⁺ ions and 6 at % Yb³⁺ ions. The ratio of the intensity of green (or red) up-conversion luminescence to the intensity of infrared Stokes luminescence increases with increasing applied voltage. The efficiency of visible emission of the light-emitting diode structures is η = 1.2 lm/W at an applied voltage of 1.5 V.     

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.     

Er3+ Sensitized Photon Upconversion Nanocrystals

Lanthanide doped upconversion nanocrystals, showing bright future in diverse fields, are typically excited by ≈700–1000 nm light when Nd³⁺ and Yb³⁺ are used as sensitizers. Thus far, extending the excitation range of upconversion nanocrystals is still a formidable challenge. Herein, a new type of upconversion nanocrystals is reported, using Er³⁺ ions as sensitizers, which can be excited by 1532 nm light located in the second near‐infrared biological window. Through Er³⁺ sensitization, upconversion emission from a series of activators, including Nd³⁺, Ho³⁺, Eu³⁺, and Tm³⁺, is obtained and can be modulated by Yb³⁺ codoping. In addition, Er³⁺ sensitized photon upconversion of Ho³⁺ and Tm³⁺ can be further enhanced by shell coating. It is found that Er³⁺ sensitized upconversion processes are mainly dependent on the energy transfer between Er³⁺ ions and activators. Considering the demonstration of anticounterfeiting by using this newly designed nanocrystal, it is anticipated that these results can bring more opportunities to upconversion nanomaterials in other aspects, ranging from lasing to super resolution imaging.