Quantum-interference and the concentration of Er3+ ion effect on left-handedness with zero absorption and large negative refractive index in Er3+:YAG crystal

The electromagnetically induced left-handedness with zero absorption and large negative refractive index was investigated in a solid Er³⁺:YAG crystal with a four-level system proposed for an atomic medium. It was found that the frequency region with simultaneous negative permittivity and negative permeability, the zero absorption intervals, and the maximum values of the negative refractive index can be adjusted by changing the signal field, the coherent field, as well as the concentration of Er³⁺ ion in crystal. It is shown that wider zero absorption intervals with a higher index of refraction can be easily obtained when the signal field is only off resonance. The slab fabricated by the left-handed solid medium Er³⁺:YAG crystal with zero absorption may be a practical candidate for designing perfect lenses.     

Theoretical comparison of Er3+-doped crystal lasers

Abstract

The theoretical results are presented from a model that has been developed to simulate the 3 μm laser transition in Er³⁺-doped laser crystals. The rate equations for the seven lowest energy levels of Er:YAG, Er:YSGG, Er:YLF and Er:BAYF have been solved numerically for both continuous wave (cw) and pulsed (Q-switched and gain switched) laser operation with direct optical pumping into the ⁴I11/2 energy level. The dependence of slope efficiency on the Er³⁺ concentration for each laser crystal was investigated for cw operation and the relative performance of Er(15%):YLF, Er(15%):BAYF, Er(50%):YAG and Er(50%):YSGG was compared for each mode of operation. The change in the slope efficiency of Er:YLF at high Er³⁺ concentration, due to additional multi-ion processes, was calculated for a wide range of rate coefficients. It was determined that the slope efficiency could be reduced by as much as 12% by these processes and thus could explain the reduction in the slope efficiency as determined experimentally for lasers using highly doped fluoride crystals as the gain medium.     

Synthesis and luminescence properties of Na+, Li+ compensated Er3+ doped CaAl4O7 phosphors

Here the green-emitting highly luminescent Er³⁺ doped, Er³⁺-Li⁺ co-doped, Er³⁺-Na⁺ co-doped CaAl₄O₇ is synthesized by Pechini method at 1000^°C. Photoluminescence (PL) of CaAl₄O₇: Er³⁺ studies have been compared with Li⁺ co-doped CaAl₄O₇: Er³⁺ and Na⁺ co-doped CaAl₄O₇: Er³⁺. Na⁺ co-doped CaAl₄O₇:Er³⁺ shows increases in luminescence intensity compared to Li⁺ co-doped CaAl₄O₇: Er³⁺ and Er³⁺ doped CaAl₄O_7. The results suggest that CaAl₄O₇:Er³⁺ phosphor can be used as efficient green-emitting phosphor in white LED. The resultant phosphor emits green color peaking at 549 nm upon 378 nm excitation. Powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques have been studied to characterize the synthesized microparticles. Further, this phosphor has good thermal stability that implies its potential to act as green phosphor in white light-emitting diodes. The effect of activator (Er³⁺), Na⁺ co-doped CaAl₄O₇:Er³⁺, and Li⁺ co-doped CaAl₄O₇:Er³⁺ phosphors luminescence spectra as well as photoluminescence life time studies were studied in detail. The results show that as the concentration of Er³⁺ in CaAl₄O₇ increases, the symmetry around the Er³⁺ ion decreases due to the creation of lattice defects in the crystal. Addition of Na⁺ and Li⁺ ions in CaAl₄O₇: Er³⁺leads to a small distortion in the local symmetry of Er³⁺ ions, thereby significantly enhancing its luminescence property. Analysis of photoluminescence life time studies of the prepared samples shows a smaller concentration quenching of Er³⁺ luminescence in charge compensated Na⁺ and Li⁺ CaAl₄O₇ phosphor.

     

Influences of Er3+ content on structure and upconversion emission of oxyfluoride glass ceramics containing CaF2 nanocrystals

Transparent 45SiO₂–25Al₂O₃–5CaO–10NaF–15CaF₂ glass ceramics doped with different content of erbium ion (Er³⁺) were prepared. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses evidenced the spherical CaF₂ nanocrystals homogeneously embedded among the glassy matrix. With increasing of Er³⁺ content, the size of CaF₂ nanocrystals decreased while the number density increased. The crystallization kinetics studies revealed that CaF₂ crystallization was a diffusion-controlled growth process from small dimensions with decreasing nucleation rate. Er³⁺ could act as nucleating agent to lower down crystallization temperature, while some of them may stay at the crystal surfaces to retard the growth of crystal. Intense red and weak green upconversion emissions were recorded for glass ceramics and their intensities increased with the increasing of Er³⁺ content under 980 nm excitation. However, the concentration quenching effect appeared when Er³⁺ doping reached 2 mol%. These results could be attributed to the change of ligand field of Er³⁺ ions due to the incorporation of Er³⁺ ions into precipitated fluoride nanocrystals.     

Infrared Luminescence of Y2O2S:Er3+ and Y2O3:Er3+

The diffuse reflectance and luminescence spectra of Y₂O₂S:Er³⁺ and Y₂O₃:Er³⁺ are studied under selective and polarized laser excitation. The results indicate that the Er³⁺ luminescence bands of yttrium oxysulfide in the 1.54-m region are one order of magnitude stronger and broader than those of yttria. Y₂O₂S:Er³⁺ is shown to contain two types of Er-related emission centers differing in the anion environment of the Er³⁺ ion.     

Lasing without population inversion in an Er3+-doped YAG crystal

Two atomic models are proposed for an Er³⁺-doped YAG crystal with application to lasing with and without population inversion. It is shown how an incoherent pumping field and coherent control coupling field can produce a laser in the presence and absence of population inversion.     

Adiabatic demagnetization of Er3+ or Nd3+ substituted YAG

The paramagnetic salts, eg alums, usually employed in adiabatic demagnetization experiments are inconvenient because of their tendency to dehydration, etc. The refractive oxides with magnetic impurities seem to be more favourable. The authors describe the results obtained with Er³⁺ and Nd³⁺ substituted yttrium aluminium garnets (YAG). Final temperatures reached after adiabatic demagnetization are comparable to those obtained with cerium magnesium nitrate. The paper illustrates the possible use of Er³⁺ and Nd³⁺ substitued in YAG for creating a very simple device for obtaining low temperatures in the mK region by adiabatic demagnetization.     

Infrared spectroscopic characterization of Na5Lu9F32 single crystals doped with various Er3+ concentrations

This work reports on optical spectra of Na₅Lu₉F₃₂ single crystals doped with various Er³⁺ concentrations from 0.5 to 5 mol%. In our improved Bridgman method, the X-ray powder diffractions were investigated and optical parameters were also calculated by the Judd–Ofelt theory. Results showed that Er³⁺ ions entered the Lu³⁺ sites successfully without causing any obvious peak changes, and the doping concentration of Er³⁺ had important influence on the Er³⁺ local structure in Na₅Lu₉F₃₂ crystals. The maximum emission intensities of ~1.5 and ~2.7 μm were obtained in present research when the doping concentration of Er³⁺ were 4 and 5 mol%, respectively, under the excitation of 980 nm LD. In these doping concentration, the maximum emission cross-sections were calculated to be 1.37 × 10^?20 cm² (~1.5 μm) and 2.1 × 10^?20 cm² (~2.7 μm). The gain cross-section at 2.7 μm was also estimated according to the absorption and emission cross section spectra. All these spectroscopic characterizations suggested that this fluoride crystal would possess promising applications in infrared lasers.     

Infrared-to-green up-conversion in Er3+, Yb3+-doped monoclinic KGd(WO4)2 single crystals

Optical spectroscopy of the green emission of erbium in KGd(WO₄)₂ (KGW) single crystals codoped with ytterbium ions is investigated. To do this, we firstly grew good-optical-quality KGW single crystals doped with Er³⁺ and Yb³⁺ at several dopant concentrations by the Top-seeded-solution-growth slow-cooling method (TSSG). Green photoluminescence of Er³⁺ in KGW host was studied at room temperature (RT) and low temperature (10 K) by means of Yb³⁺ sensitization after infrared excitation at 981 nm (10194 cm⁻¹). We calculated the emission and gain cross-sections and compared these with those of other known Er³⁺-doped laser materials like LiYF₄ :Er (YLF:Er) and Y₃Al₅O₁₂:Er (YAG:Er) at RT. Our study also focused on determining the optimal concentration of ions for generating the most intense green emission. We measured the lifetime of the green emission after infrared pump at several Yb³⁺ concentrations. From the low-temperature emission experiments, we determined the energy position of the sublevels of the ground state of erbium.     

Efficient up-conversion emission and energy transfer in LaAlO3 doped with Er3+, Ho3+, and Yb3+ ions

The spectroscopic properties of LaAlO₃ polycrystals doped with Er³⁺, Ho³⁺ and Yb³⁺ ions have been investigated. Very efficient up-conversion emission occurs upon IR excitation. The strongest luminescence has been observed for a sample doped with Er³⁺, Ho³⁺, and Yb³⁺ ions simultaneously and annealed at 1500 °C. An efficient energy transfer to Yb³⁺ ions is observed when Er³⁺ or Ho³⁺ ions are excited. The energy transfer mechanisms are proposed.     

Effect of Yb concentration on the upconversion of Er ion doped La2O3 nanocrystals under 980 nm excitation

The effect of Yb³⁺ concentration on the upconversion of La₂O₃:Yb³⁺, Er³⁺ nanocrystals was reported. Green (about at 530 and 549 nm) and red (around at 672 nm) upconversion emissions under 980 nm excitation were observed at room temperature. It was found that the ratio of green to red upconversion emission intensity is considered as a function of Yb³⁺ ion concentration. Of the samples doped with varying Er³⁺ or constant Er³⁺ ion concentration, it can be observed that the intensity ratio drastically decreases with an Yb³⁺ ion concentration increase and the Yb³⁺ ions concentration is around 3 mol% as the emission intensity ratio of green to red upconversion is close to 1.     

Visible luminescence properties of Er3+–Pr3+ codoped fluorotellurite glasses

Er³⁺ and Pr³⁺ codoped fluorotellurite glasses has been synthesized. The PL spectrum revealed that the intensity of Er³⁺ characteristic emission was enhanced as Pr³⁺ concentration increased. Due to small mismatch between the energy level of Er³⁺: ⁴F_7/2 and Pr³⁺: ³P₀ resonant energy was possibly transferred between them. While Pr³⁺ concentration kept increasing, both Pr³⁺ and Er³⁺ concentration quenching occurred. These glasses with the controllable CIE coordinates might be a potential candidate for the widely application such as solid state multicolor display.     

Fabrication of Er3+-doped LaOCl nanostructures with upconversion and near-infrared luminescence performances

LaOCl:Er³⁺ nanofibers and nanobelts were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl powders as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Er³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameter of LaOCl:Er³⁺ nanofibers and the width of nanobelts respectively were 161.15 ± 18.11 nm and 6.11 ± 0.19 μm under the 95 % confidence level, and the thickness of nanobelts was 116 nm. Up-conversion (UC) emission spectra analysis manifested that LaOCl:Er³⁺ nanostructures exhibited strong green and red UC emission centering at 525, 548 and 671 nm, respectively attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_l5/2 energy levels transitions of Er³⁺ ions under the excitation of a 980-nm diode laser. It was found that the relative intensities of green and red emissions vary obviously with the changing of concentration of Er³⁺ ions, and the optimum molar percentage of Er³⁺/(La³⁺+Er³⁺) ions was 5 % in the LaOCl:Er³⁺ nanostructures. The LaOCl:x %Er³⁺ nanobelts have higher UC emission (both red and green) intensity than the counterpart nanofibers. Moreover, the near-infrared characteristic emissions of LaOCl:Er³⁺ nanostructures were achieved under the excitation of a 532-nm laser. Commission Internationale de L’Eclairage analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Er³⁺ ions, which could be applied in the fields of optical telecommunication and optoelectronic devices. The UC luminescent mechanism of LaOCl:Er³⁺ nanostructures were also proposed.     

Frequency upconversion fluorescence studies of Er/Yb-codoped KNbO3 phosphors

Different concentrations of Er³⁺ and Yb³⁺ ions-doped potassium niobate (K_0.9NbO₃:Yb_(x)Er_{(0.1 − x)} for x = 0, 0.01, 0.05, 0.09 and 0.1) polycrystalline powder phosphors were prepared by the conventional solid state reaction method and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Energy transfer and upconversion fluorescence properties of the Yb³⁺ and Er³⁺-codoped phosphors have been discussed. The XRD data has shown mono-phase for pure KNbO₃ while the doped samples represented additional phase formation. The SEM micrographs represented the rectangular crystal growth habit for the KNbO₃ phosphors when doped with 0.1 mol of Er³⁺ ions. An intense green emission at 557 nm along with a red emission at 674 nm was observed when the doped samples were excited with 975 nm IR radiation. The upconversion mechanism has been discussed based on the excited state absorption and energy transfer mechanisms.     

Effect of vapor transport equilibration and Mg doped on the luminescence of Er:LiNbO3

Luminescence properties of the congruent and vapor transport equilibration (VTE) treated Er:LiNbO₃ and Er:Mg:LiNbO₃ crystals were recorded at room temperature. It is observed that VTE treatment could enhance the emission intensity of Er³⁺ ions and doping with MgO would weaken it in the visible spectra. As a result, the luminescence intensity of Er³⁺ ions in the VTE treated Er:Mg:LiNbO₃ crystal increased up to 2.2 times than that in the congruent Er:LiNbO₃ crystal. In addition, both VTE treatment and doping with MgO result in some changes of the relative emission intensity of some peaks in the visible emission spectra. In the infrared emission spectra, the luminescence peak at 1540 nm of Er³⁺ ions shifts towards the larger wavelength when the Er:LiNbO₃ crystals were treated using VTE or doped with MgO. The changes in crystalline environment of Er³⁺ ions due to VTE treatment or doping with Mg²⁺ play a key role in these phenomena.     

Growth,first-principles simulations and near-infrared optical properties of rare earth (Nd3+, Er3+)-doped CeF3 crystals for laser applications

Nd³⁺:CeF₃ and Er³⁺:CeF₃ crystals with different doping concentrations were successfully grown by the Bridgman method. The physicochemical parameters, such as crystal structure and phonon vibration energy were obtained by XRD and Raman tests. The results show that rare earth (Nd³⁺ or Er³⁺) does not change the hexagonal phase structure of the crystal, and the doping of rare earth ions does not change the maximum phonon frequency. The measured results are 388 and 392 cm^??1, respectively, which are similar to CeF₃ single crystal and half of common oxide crystal. According to the first principle, the difference charge density of the two crystals can be intuitively obtained. The calculated band gap values of the two crystals are 2.91 and 4.37 eV, respectively, which are similar to the results of absorption spectrum measurement. The NIR luminescence performance of Nd³⁺:CeF₃ crystal was tested by 808 nm pump. When the doping concentration reached 2 at%, the emission intensity was the strongest at 1064 nm (⁴F_3/2→⁴I_11/2). The luminescence properties of Er³⁺:CeF₃ crystal at 1550 nm (⁴I_13/2→⁴I_15/2) were tested by 980 nm pump. The emission intensity keeps the highest when the doping concentration reaches 3 at%. The concentration quenching and the dipole-dipole interaction in crystals are studied using energy transfer theory, and the J-O strength parameters of crystals are calculated. The results show that Nd³⁺:CeF₃ and Er³⁺:CeF₃ crystals have excellent properties and excellent near-infrared luminescence performance, which has great potential in laser applications.

     

Two- and three-photon upconversion of LaOBr:Er3+

In this work, the LaOBr:Er³⁺ (0.1%) powders were prepared by solid state reaction. The structural properties of LaOBr:Er³⁺ were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The results show that LaOBr:Er³⁺ has low phonon energy, which indicate that LaOBr:Er³⁺ may have high luminescent efficiency. Under excitation into ⁴I_11/2 level of Er³⁺ ions by 980 nm laser, the two- and three-photon upconverted luminescence of LaOBr:Er³⁺ were recorded. The most intense emissions were come from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transitions. The upconversion mechanisms were studied in detail through laser power dependence, and results show that excited state absorption is responsible for the upconversion. The upconversion properties indicate that LaOBr:Er³⁺ may be used in upconversion phosphors.     

Emission properties of highly doped Er3+ fluoroaluminate glass

Er³⁺-doped fluoroaluminate (AYF) glass was compared with fluorozirconate (ZBLAN) and tetraphosphate (PE) glass as a host material for 1.54-μm emission. Experimental results show that the Er³⁺:AYF glass has a smaller concentration quenching and much stronger intensity for the 1.54-μm emission. In high dopant, the 1.54-μm emission is two times stronger in Er³⁺/AYF glass than in ZBLAN glass, and 10 times stronger than in PE glass.     

Emission properties of polymer composites doped with Er3+:Y2O3 nanopowders

In this work we report the recent results of our investigation on visible emission properties of the PMMA-based polymer nanocomposites doped with Er³⁺:Y₂O₃ nanopowders. The set of active nanopowders, and polymer films, differing in active ions concentration, was characterized with respect of their luminescent properties in the green spectral range, available to a limited extent for semiconductor lasers. In particular – the concentration dependent emission spectra and fluorescence dynamics profiles were measured under direct (single photon) and up-converted excitation, enabling the comparison of luminescent properties of developed nanocomposite materials and original nanopowders, optimization of erbium dopant concentration as well as discussion of excitation mechanisms and analysis of the efficiency of depopulation processes.     

Luminescence of GaS:Er<Superscript>3+</Superscript> and GaS:Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> layered crystals

Data are presented on the 300-K photoluminescence in GaS crystals doped with Er³⁺ or codoped with Er³⁺ and Yb³⁺. IR excitation (λ_ex = 976 nm) gives rise to anti-Stokes luminescence in GaS:Er³⁺ (0.1 at %) and GaS:Er³⁺,Yb³⁺ (0.1 + 0.1 at %) and leads to an increased intensity of the emission due to the ⁴ I _11/2 → ⁴ I _15/2 transitions. The anti-Stokes luminescence is shown to result from consecutive absorption of two photons by one Er³⁺ ion, and the increased intensity of Er³⁺ luminescence in GaS: Er³⁺,Yb³⁺ is due to energy transfer from Yb³⁺ to Er³⁺.