Antiferromagnetic interactions in Er-doped SnO<Subscript>2</Subscript> DMS nanoparticles

Diluted magnetic semiconductor (DMS) nanoparticles of Sn_1−x Er _x O₂ (x = 0.0, 0.02, 0.04, and 0.1) were prepared by sol–gel method. The X-ray diffraction patterns showed SnO₂ rutile structure for all samples with no impurity peaks. The decrease in crystallite size with Er concentration was confirmed from TEM measurements (from 12 to 4 nm). The UV–Visible absorption spectra of Er-doped SnO₂ nanoparticles showed blue shift in band gap compared to undoped SnO₂. The electron spin resonance analysis of Er-doped SnO₂ nanoparticles indicate Er³⁺ in a rutile lattice and also decrease in intensity with Er concentration above x = 0.02. Temperature-dependent magnetization studies and the inverse susceptibility curves indicated increased antiferromagnetic interaction with Er concentration.     

Visible luminescence of nanocrystalline AlN:Er thin film by co-deposition of AlN,Er, and SiO2

We report a visible luminescence of Er³⁺ ions in an amorphous-nanocrystalline AlN:Er thin film prepared by co-deposition using AlN, Er, and SiO₂ targets. A PL emission spectrum of Er³⁺ in the AlN:Er film annealed at 750 °C showed a strong bluish green emission of Er³⁺ in the amorphous-nanocrystalline AlN:Er thin film, which is attributed to the intra-4fEr³⁺ transitions of ²H_11/2 → ⁴I_15/2 and ⁴F_7/2 → ⁴I_15/2. It was found that crystallite diameters were between 3 and 5 nm by high-resolution transmission electron microscopy. The occurrence of the strong Er³⁺ emission in the annealed AlN:Er thin film with a mixture of amorphous and nanocrystalline phases may be contributed to an increase in the number of excitation Er³⁺ centers and a presence of oxygen related to Er³⁺ excitation and recombination process in the AlN:Er thin film.     

Luminescence characteristics of cobalt doped TiO2 nanoparticles

TiO₂ nanoparticles doped with two different concentrations of Cobalt, 0.02 and 0.04 mol, are prepared by sol–gel method. The crystalline phase of the doped and undoped nanoparticles and particle sizes are observed with X-ray diffraction and transmission electron microscope. FTIR confirms the bonding interaction of Co²⁺ in TiO₂ lattice framework. The UV absorption spectra of the doped material shows two absorption peaks in the visible region related to d–d electronic transitions of Co²⁺ in TiO₂ lattice. Compared to undoped TiO₂ nanoparticles, the cobalt doped samples show a red shift in the band gap. Steady state photoluminescence spectra give emission peaks related to oxygen defects. The decrease in the intensity ratio of UV/visible emission peaks confirms distortion of structural regularity and formation of defects after doping. The intensity ratio of different visible emission peaks is nearly same for undoped and 0.02 Co²⁺. However, this ratio decreases profoundly at 0.04 Co²⁺, due to concentration quenching effect. Photoluminescence excitation spectra, recorded at 598 nm emission wavelength, give different excitation peaks associated with oxygen vacancies and Co²⁺. Time resolved photoluminescence spectra give longer decay time for doped samples, indicating longer relaxation of conduction band electrons on the defect and on dopant sites.     

2μm emission performance in Ho3+ doped fluorophosphate glasses sensitized with Er3+ and Tm3+ under 800 nm excitation

The spectroscopic properties and energy transfer mechanisms in Ho³⁺ doped fluorophosphate glasses sensitized by Er³⁺ and Tm³⁺ at the 2 μm region are investigated. The absorption spectra and fluorescence spectra of the Tm–Ho doubly-doped glass system and Er–Tm–Ho triply-doped glass system are measured. According to the absorption spectra, the Judd–Ofelt parameters and spontaneous transition probability are calculated and compared with those of other glass hosts. From the fluorescence spectra, the fluorescence intensity of Er–Tm–Ho glass system at 2.0 μm is 0.95 and larger than that of the Tm–Ho glass system, which is 0.69. Meanwhile, the 2.0 μm to 1.8 μm and 2.0 μm to 1.53 μm peak intensity ratios in the Er–Tm–Ho glass system are 8.63 and 22.79, respectively, suggesting sufficient energy transfer between Er³⁺, Tm³⁺ and Ho³⁺ ions. In addition, the pumping schemes and energy transfer mechanisms of Tm–Ho doubly-doped and Er–Tm–Ho triply-doped glasses are discussed. The study indicates that the Er–Tm–Ho triply-doped glass system is a significant sensitized way pumped at 800 nm in fluorophosphate glasses for 2 μm applications.     

Dopant occupancy and optical properties of Er3+ in Er/Zn-codoped lithium niobate crystal

The effect of Zn²⁺ ion on the dopant occupancy and optical characteristic of Er³⁺ ion in Er/Zn-codoped LiNbO₃ crystal is reported. The intense 1.54 μm and relatively weak green upconversion emissions are observed for Er (1 mol%)/Zn (6 mol%):LiNbO₃ crystal. The OH^? absorption and the time-resolved spectra show that the Zn²⁺ codoping decreases the threshold concentration of Er³⁺ ion in Er/Zn-codoped LiNbO₃ crystal. The experimental results here imply that the potential application of Er³⁺-doped LiNbO₃ crystal can be designed and optimized on the basis of the theoretical investigations.     

Avidin conjugation to up-conversion phosphor NaYF4:Yb3+, Er3+ by the oxidation of the oligosaccharide chains

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. After being functionalized with SiO₂–NH₂ layer, these NaYF₄:Yb³⁺, Er³⁺ nanoparticles can conjugate with activated avidin molecules (activated by the oxidation of the oligosaccharide chain). The as-formed NaYF₄:Yb³⁺, Er³⁺ nanoparticles, NaYF₄:Yb³⁺, Er³⁺ nanoparticles functionalized with amino groups, avidin conjugated amino-functionalized NaYF₄:Yb³⁺, Er³⁺ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), UV/Vis absorption spectra, and up-conversion luminescence spectra, respectively. The biofunctionalization of the NaYF₄:Yb³⁺, Er³⁺ nanoparticles has less effect on their luminescence properties, i.e., they still show the up-conversion emission (from Er³⁺, with ⁴S_3/2 → ⁴I_15/2 at ~540 nm and ⁴F_9/2 → ⁴I_15/2 at ~653 nm), indicative of the great potential for these NaYF₄:Yb³⁺, Er³⁺ nanoparticles to be used as fluorescence probes for biological system.     

Yb effect on the spectroscopic properties of Er-Yb codoped SnO2 thin films

We have investigated the optical properties of sol-gel thin films of tin dioxide (SnO₂) codoped with Er³⁺-Yb³⁺ as a function of Yb³⁺ concentration. The Judd-Ofelt model has been applied to absorption intensities of Er³⁺ (4f¹¹) transitions to establish the so-called Judd-Ofelt intensity parameters: Ω₂, Ω₄, Ω₆. Various spectroscopic parameters were obtained to evaluate their dependence and the potential of the samples as a laser material in the eye-safe laser wavelength (1.53 μm) as a function of Yb³⁺ concentration. An amelioration of the quality factor Ω₄/Ω₆ was found with Yb content. Both the IR photoluminescence (PL) intensity and the up-conversion emission, from Er³⁺ ion in SnO₂, were found to increase with Yb concentration. We show that the Yb³⁺ ion acts as sensitizer for Er³⁺ ion and contributes largely to the improvement of the spectroscopic properties of SnO₂:Er. The mechanism of up-conversion emission is discussed and a model is proposed. The results showed that sol-gel SnO₂ is promising gain media for developing the solid-state 1.5 μm optical amplifiers and tunable up-conversion lasers.     

The influence of Zn2+ ion on the 1.5 μm laser properties of LiNbO3 crystal heavily doped with Er3+ ion

The spectral characteristics of 1.54 μm emission in a series of Zn/Er:LiNbO₃ crystals with heavy Er content and variable Zn content were reported. The inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration of Er³⁺ ion in the crystal. The absorption and emission spectra of Zn/Er:LiNbO₃ crystals were measured. Based on Judd–Ofelt theory, the spectral parameters such as intensity parameters Ω_t (t=2, 4 and 6), transition strengths, radiative transition probabilities, radiative lifetime and fluorescence branching ratio have been obtained in Zn/Er:LiNbO₃ system. The emission cross section corresponding to ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ion was obtained according to Füchtbauer–Ladenburg theory. The gain cross section of Er:LiNbO₃ crystal codoped with 6 mol% Zn²⁺ ions were also discussed in this work.     

Sensitisation of erbium emission by silicon nanocrystals-doped SnO2

SnO₂ thin films undoped and doped with antimony (Sb), erbium (Er) and Si nanocrystals (Si-nc) have been grown on silicon (Si) substrate using sol-gel method. Room-temperature photoluminescence (PL) measurement of undoped SnO₂, under excitation at 280 nm, shows only one broad emission at 395 nm, which is related to oxygen vacancies. The PL of Er³⁺ ions was found to be enhanced after doping SnO₂ with Sb and Si-nc. The excitation process of Er is studied and discussed. The calculation of cross-section suggests a sensitisation of Er PL by Si-nc.     

Crystal growth and optical properties of Cr3+, Er3+, RE3+: Gd3Ga5O12 (RE=Tm,Ho, Eu) for mid-IR laser applications

In this paper we report on the optical properties of triply Cr³⁺, Er³⁺, and RE³⁺ (RE=Tm, Ho, Eu) doped Gd₃Ga₅O₁₂ crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr³⁺ ion highly increases the absorption pump power and the three kinds of co-doped RE³⁺ ions depopulate the Er:⁴I_13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ～3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others.     

Influence of MgO codoping on the optical properties of Er3+-doped near-stoichiometric LiNbO3

Four near-stoichiometric lithium niobate (NSLN) crystals codoped with Er³⁺ (1 mol%) and MgO (0, 0.5, 1.0, and 2.0 mol%) were grown from K₂O-based flux in air using top seeded solution growth technique. The [Li]/[Nb] ratio, estimated from the blueshift of ultraviolet absorption edge, is 97.2% in NSLN:Er. MgO; codoping can increase the segregation coefficient of Er³⁺ in NSLN:Er:MgO crystal. The photorefractive damage threshold is enhanced by three orders of magnitude for NSLN:Er codoped with 1 mol% MgO, it coincides with the peak shift of OH⁻ absorption spectrum from 3481 to 3535 cm⁻¹. Judd–Ofelt theory based on absorption spectra is used to analyze the influence of MgO concentration on the Judd–Ofelt intensity parameter, transition strength, fluorescence branching ratio, and stimulated emission cross section. From the time-resolved emission spectra and the comparison among emission spectra, two Er³⁺ crystal-field sites are ascertained in NSLN:Er codoped with 2 mol% MgO, this coincides with the bimodal structure in X-ray photoelectron spectrometry spectra. The upconversion processes under pulse excitation is proposed based on the pump energy dependence and decay kinetics. The distribution of Er³⁺-clustered sites in NSLN:Er:MgO series is discussed based on the nonexponential decay curves monitored at 550 nm under two-photon excitation.     

Electron trapping center and SnO2-doping mechanism of indium tin oxide

Indium tin oxide (ITO) and Er³⁺-doped ITO powders were prepared by a conventional ceramic method. The density of ITO powders and optical absorption spectra of Er³⁺ ions in Er³⁺-doped ITO were measured as a function of the SnO₂ doping level. The results obtained were discussed in terms of the trapping center for immobile electrons in ITO. Observed densities of ITO powders were in good agreement with those calculated from their lattice parameters, assuming that the immobile electrons were trapped at the excess interstitial oxygen. The optical absorption spectra of Er³⁺-doped ITO indicated that some In³⁺ ions in ITO were surrounded by 7 and/or 8 oxygen ions; the increase in the coordination number of In³⁺ from 6 in In₂O₃ to 7 and/or 8 in ITO must be caused by the introduction of excess interstitial oxygen into the quasi-anion site in the C-typerare-earth lattice upon SnO₂ doping. It was concluded that the immobile electrons in ITO are trapped at the excess interstitial oxygen, and that the mechanism of conduction carrier generation and compensation upon SnO₂ doping into In₂O₃ can be expressed by the defect equation, 2SnO₂?2Sn_In·+2(1-z)e^′+zO_i ^′′+3O_O ^×+(1-z)/2O₂. Received: 26 November 1999 / Accepted: 20 April 2000 / Published online: 13 September 2000     

Crystalline-structure-dependent green and red upconversion emissions of Er-Yb-Li codoped TiO2

Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er³⁺, 10 mol% Yb³⁺ and 0-20 mol% Li⁺ codoped TiO₂ [1Er10Yb(0-20)Li:TiO₂] nanocrystals. The crystalline structures of 1Er10Yb(0-20)Li:TiO₂ were divided into three parts by the addition of Yb³⁺ and Li⁺. Both green and red upconversion emissions were observed from the ²H_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ in Er³⁺-Yb³⁺-Li⁺ codoped TiO₂, respectively. The green and red upconversion emissions of 1Er:TiO₂ were enhanced significantly by Yb³⁺ and Li⁺ codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions (I_green/I_red) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er³⁺ and Yb³⁺ as well as the distortion of crystal field symmetry of Er³⁺ caused by the dissolving of Li⁺ at lower Li⁺ codoping concentration and the phase transformation at higher Li⁺ concentration. It is concluded that codoping with ions of smaller ionic radius like Li⁺ can efficiently improve the upconversion emissions of Er³⁺ or other rare-earth ions doped luminsecence materials.     

Mesoporous silica-coated NaYF4:Yb3+, Er3+ particles for drug release

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. These NaYF₄:Yb³⁺, Er³⁺ nanoparticles can be coated with mesoporous silica using nonionic triblock copolymer EO₂₀PO₇₀EO₂₀ (P 123) as structure-directing agent and other materials. The composites can load ibuprofen and release the drug in the phosphate buffer solution (PBS). The composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption/desorption isotherms, fluorescence spectra, and UV/Vis absorption spectra, respectively. The composites have the mesoporous structure. In addition, the composites emit red fluorescence (from Er³⁺) under 980 nm near infrared laser excitation, which can be used as fluorescent probes in the drug-delivery system.     

Doubly doped BaY2F8:Er,Nd VUV scintillator

Doubly doped BaY₂F₈:Er,Nd scintillation crystals were grown by modified micro-pulling-down method. The Er co-doping was chosen to enhance the energy transfer from the host lattice to the Nd³⁺ luminescence center via the 5d-levels of Er³⁺, which can be enabled by the overlap of Er³⁺ 5d-4f emission spectrum with the Nd³⁺ 4f-5d absorption. The energy transfer was clearly evidenced in the BaY₂F₈:Er,Nd. The processes are complicated by energy migration to killer centres and/or cross-relaxation processes. The luminescence and energy transfer mechanism are discussed.     

Preparation and photocatalytic degradation of erbium doped titanium dioxide nanorods

Photocatalytic degradation of methylene blue (MB) in water was examined using Er³⁺-doped TiO₂ (Er–TiO₂) nanorods prepared by a sol–gel derived electrospinning, calcination, and subsequent mechanical grinding. Different concentrations of Er dopant in the range of 0–1.0 mol% were synthesized to evaluate the effect of Er content on the photocatalytic activity of TiO₂. Among Er³⁺–TiO₂ catalysts, the 0.7 mol% Er³⁺–TiO₂ catalyst showed the highest MB degradation rate. The degradation kinetic constant (k) increased from 1.0 × 10^?3 min^?1 to 5.1 × 10^?3 min^?1 with the increase of Er³⁺ doping from 0 to 0.7 mol%, but decreased down to 2.1 × 10^?3 min^?1 when Er³⁺ content was 1.0 mol%. It can be concluded that the degradation of MB under UV radiation was more efficient with Er³⁺–TiO₂ catalyst than with pure TiO₂. The higher activity might be attributed to the transition of 4f electrons of Er³⁺ and red shifts of the optical absorption edge of TiO₂ by erbium ion doping.     

Growth, polarized spectral properties, and 1.5–1.6 μm laser operation of Er:Yb:Sr3Gd2(BO3)4 crystal

An Er:Yb:Sr₃Gd₂(BO₃)₄ crystal was grown by the Czochralski method. The polarized spectral properties of the crystal were investigated, including the polarized absorption and fluorescence spectra and fluorescence decay. The fluorescence quantum efficiency of the upper laser level ⁴I_13/2 of Er³⁺ ions and the efficiency of the energy transfer from Yb³⁺ to Er³⁺ ions were calculated. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 1.6 W quasi-cw laser at 1.5–1.6 μm with a slope efficiency of 18% and an absorbed pump threshold of 5.9 W was achieved in a 1.8-mm-thick Z-cut Er:Yb:Sr₃Gd₂(BO₃)₄ crystal. This crystal has a flat and broad gain curve at 1.5–1.6 μm and so is also a potential gain medium for tunable and short pulse lasers.     

VUV-UV-visible luminescence of Nd3+, Er3+ and Tm3+ in LiLuF4 single crystal host

An overlook of absorption and luminescence characteristics of Nd³⁺, Er³⁺ and Tm³⁺ centers in LiLuF₄ single crystal is provided. Single crystal doped with the mentioned RE ions were prepared by micro-pulling-down technique in the form of few cm long rods with the diameter of about 2 mm. Excitation and emission spectra and fast decay kinetics in VUV spectral region were measured at SUPERLUMI station at synchrotron DESY, Hamburg and characterization was further completed in UV-visible region at conventional spectrophotometers. Observed absorption and emission peaks are ascribed to the 5d–4f and 4f–4f optical transitions in the doped rare earth ions. Concentration dependence of the decay kinetics is discussed.     

Sol–gel glass-ceramics comprising rare-earth doped SnO<Subscript>2</Subscript> and LaF<Subscript>3</Subscript> nanocrystals: an efficient simultaneous UV and IR to visible converter

Abstract  

We report a novel class of nanostructured glass-ceramics comprising two co-existing rare-earth doped nanocrystalline phases, SnO₂ semiconductor nanocrystal (quantum dot), and LaF₃, presenting sizes at around 4.6 and 9.8 nm, respectively, embedded into a silica glass matrix for an efficient simultaneous UV and IR to visible photon conversion. On one hand, the wide and strong UV absorption by SnO₂ quantum dot and subsequent efficient energy transfer to Eu³⁺ and, on the other hand, the also very efficient IR to visible up-conversion with the pair Yb³⁺–Er³⁺ partitioned into low phonon LaF₃ nanocrystalline environment, yield to visible emissions with application in improving the spectral response of photovoltaic solar cells.     

Scintillation properties of Er-doped Y3Al5O12 single crystals

Er-doped Y₃Al₅O₁₂ single crystals with different Er concentrations of 0.1, 1.0, 10, 30, and 50% were grown by the micro-pulling down method. There were several absorption lines due to the Er³⁺ 4f-4f transitions in the transmittance spectra and these lines correspond to the transitions from the ground state of ⁴I_15/2 to the excited states. The photo- and radio-luminescence spectra showed Er³⁺ 4f-4f emissions. Relative light yield under 5.5 MeV alpha-ray irradiation of Er 0.1%:Y₃Al₅O₁₂ was estimated to be 63% of that of Bi₄Ge₃O₁₂.