Single-crystal Erbium Research Articles

Giant optical gain in a single-crystal erbium chloride silicate nanowire

Rare-earth optical materials with large optical gain are of great importance for a wide variety of applications in photonics and quantum information due to their long carrier lifetimes and quantum coherence times, especially in the realization of efficient lasers and amplifiers. Until now, such materials have achieved a gain of less than a few dB cm–1, rendering them unsuitable for applications in nanophotonic integrated circuits. Here, we report the results of the signal enhancement and transmission experiments on a single-crystal erbium chloride silicate nanowire. Our experiments demonstrate that a net material gain over 100 dB cm–1 at wavelengths around 1,530 nm is possible due to the nanowire's single-crystalline material quality and its high erbium concentration. Our results establish that such rare-earth-compound nanowires are a potentially important class of nanomaterials for a variety of applications including, for example, subwavelength-scale optical amplifiers and lasers for integrated nanophotonics, and quantum information. Erbium chloride silicate nanowire promises optical gain for nanophotonic circuits.

Silicon-erbium ytterbium silicate nanowire waveguides with optimized optical gain

Single-crystal erbium silicate nanowires have attracted considerable attention because of their high optical gain. In this work, we report the controlled synthesis of silicon-erbium ytterbium silicate core-shell nanowires and fine-tuning the erbium mole fraction in the shell from x = 0:3 to x = 1:0, which corresponds to changing the erbium concentration from 4:8 × 1021 to 1:6 × 1022 cm-3. By controlling and properly optimizing the composition of erbium and ytterbium in the nanowires, we can effectively suppress upconversion photoluminescence while simultaneously enhancing near-infrared emission. The composition-optimized nanowires have very long photoluminescence lifetimes and large emission cross-sections, which contribute to the high optical gain that we observed. We suspended these concentration-optimized nanowires in the air to measure and analyze their propagation loss and optical gain in the near-infrared communication band. Through systematic measurements using wires with different core sizes, we obtained a maximum net gain of 20±8 dB·mm-1, which occurs at a wavelength of 1534 nm, for a nanowire with a diameter of 600 nm and a silicon core diameter of 300 nm.

Single crystal erbium compound nanowires as high gain material for on-chip light source applications

Integrated photonics requires high gain optical materials in the telecom wavelength range for optical amplifiers and coherent light sources. Erbium (Er) containing materials are ideal candidates due to the 1.5 μm emission from Er3+ ions. However, the Er density in typical Er-doped materials is less than 1020 cm–3, thus limiting the maximum optical gain to a few dB/cm, too small to be useful for integrated photonic applications. Er compounds could potentially solve this problem since they contain much higher Er3+ density. So far the existing Er compounds suffer from short lifetime and strong upconversion effects, mainly due to poor crystal qualities. Recently, we explore a new Er compound: erbium chloride silicate (ECS, Er3(SiO4)2Cl) in the form of nanowire, which facilitates the growth of high quality single crystal with relatively large Er3+ density (1.62 × 1022 cm–3). Previous optical results show that the high crystal quality of ECS material leads to a long lifetime up to 1 ms. The Er lifetime-density product was found to be the largest among all the Er containing materials. Pump-probe experiments demonstrated a 644 dB/cm signal enhancement and 30 dB/cm net gain per unit length from a single ECS wire. As a result, such high-gain ECS nanowires can be potentially fabricated into ultra-compact lasers. Even though a single ECS nanowire naturally serves as good waveguide, additional feedback mechanism is needed to form an ultra-compact laser. In this work, we demonstrate the direct fabrication of 1D photonic crystal (PhC) air hole array structure on a single ECS nanowire using focused ion beam (FIB). Transmission measurement shows polarization-dependent stop-band behavior. For transverse electric (TE) polarization, we observed stop-band suppression as much as 12 dB with a 9 μm long airholed structure. Through numerical simulation, we showed that Q-factor as high as 11000 can be achieved at 1.53 μm for a 1D PhC micro-cavity on an ECS nanowire. Such a high Q cavity combined with the high material gain of ECS nanowires provides an attractive solution for ultra-compact lasers, an important goal of this research.

Long lifetime, high density single-crystal erbium compound nanowires as a high optical gain material

Erbium-containing materials of long lifetime and high Er density are important for achieving strong luminescence and high optical gain in compact integrated photonics devices. We have systematically studied the lifetime and crystal quality as a function of growth conditions for an erbium compound that we recently reported, erbium chloride silicate (ECS). The lifetime for the best quality ECS nanowires can be as long as 540 μs, the longest for high-density Er-materials, representing a lifetime-density product as high as 8.7 × 1018 s cm−3. Such high density, long lifetime erbium materials can find many interesting applications such as compact lasers or amplifiers.

Single-crystal erbium chloride silicate nanowires as a Si-compatible light emission material in communication wavelength

We report on the first synthesis and structural characterizations of a new Erbium (Er) compound, the erbium chloride silicate (ECS, Er3Cl(SiO4)2) single crystal in a Si-ECS core-shell nanowire form. The Er-concentration in ECS at 1.6x1022 cm−3 is three orders of magnitude higher than that of the Er-doped materials. Photoluminescence spectra at both low and room temperatures exhibit well separated sharp emission lines in the near infrared region. The new single-crystal erbium-compound nanowires provide a unique Si-compatible material for high-gain light emission in communication wavelength and for many other photonic applications.

Control of thick single crystal erbium oxide growth on (1 1 1) silicon

Single crystal erbium oxide films up to 150 nm thick were grown directly on Si (1 1 1) substrates by molecular beam epitaxy (MBE). The formation of erbium silicide interfacial phases was successfully suppressed by control over critical growth parameters. Wafers were characterized by in situ optical reflectometry and post-growth X-ray diffraction, ellipsometry, photoluminescence mapping and electron microscopy. By correlating these results we have established MBE growth protocols such that silicide formation can be detected immediately during growth, thereby enabling a more production-oriented approach to growth of erbium oxide films.

Growth and optical properties of Er,Yb:YAl 3(BO 3) 4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl 3(BO 3) 4(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl 3(BO 3) 4 crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl 3(BO 3) 4 crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.

Crystal growth and spectroscopic properties of Er:La3Ga5SiO14 single crystals

In this paper, single crystal of erbium (Er) doped La3Ga5SiO14 has been grown along the c-axis by using the Czochralski method. The crystal structure still belongs to space group P321. The absorption spectrum and fluorescence spectrum of the Er3+:La3Ga5SiO14 crystal were measured at room temperature. The segregation coefficients of Er3+ in La3Ga5SiO14 crystal were measured by X-ray fluorescence analysis (XRF). For the 1mol% doping level in the melt, the distribution coefficient of Er3+ was determined to be 0.117wt%.

Neutron Diffraction Study of the p - T Phase Diagram for Erbium

Electrical resistivity measurements performed on a single crystal of erbium as a function of temperature and hydrostatic pressure have provided a preliminary p - T phase diagram. The results have been interpreted in terms of a model for the magnetic structures of Er deduced from neutron diffraction studies at ambient pressure. This model predicted the existence of a magnetic structure with a wave vector of Q =2/7 c * at 4.2 K, when the applied pressure is larger than 3 kbar. This paper reports a neutron diffraction study of erbium made in the temperature range of 4 to 100 K, at pressures between 0.5 and 6 kbar. We have observed the predicted suppression of the low temperature conical ferromagnetic phase and the emergence of a new phase with Q =8/33 c *. The neutron diffraction measurements has enabled us to identify the various phases that develop from the cycloidal phases previously observed at atmospheric pressure.

On the phase diagram of erbium

We have examined the magnetic phase diagram of single crystal erbium in applied magnetic fields up to 5.5 T along the c and b-axes using electrical resistance versus temperature and magnetoresistance measurements. The phase diagram for the field along the c-axis generally agrees well with the previous neutron scattering studies by Lin et al. (Phys. Rev. B., 45 (1992) 12873) and McMorrow et al. (J. Phys. Condens. Matter, 4 (1992) 8599). We have observed a splitting of the longitudinal Néel transition as a function of applied magnetic field, and a multicritical point at a field of 2.65 T and 71 K leading to previously unobserved magnetic phases. The phase diagram for the field along the b-axis of Erbium has been determined for the first time. Recently, Jehan et al. (Phys. Rev. B, 50 (1994) 3085) have studied the a-axis phase diagram using neutron scattering. We have used their data along the a-axis in identifying the magnetic structure of our phase diagram for Er along the b-axis.

The b-axis magnetic phase diagram of erbium

We have used resistance versus temperature and magnetoresistance measurements to construct the b-axis magnetic phase diagram of single-crystal erbium. The magnetic phase transitions are identified as slope changes in resistivity data at constant applied magnetic fields along the b-axis. At zero field we observe transitions at about 19 K , 22 K, 42 K, 48 K, 53 K , and 87 K . The dependence of these transition temperatures as a function of applied magnetic fields ( H) allowed us to construct an H - T phase diagram of single-crystal erbium along the b-axis. We observe that the zero-field 42 K and 87 K transitions do not have significant magnetic field dependence whereas the zero-field transitions at 48 K and 53 K are highly field dependent. Recently, Jehan et al have constructed the a-axis magnetic phase diagram of erbium using neutron diffraction and magnetization measurements. We have utilized their data to provide information concerning the magnetic structure in some areas of our phase diagram.

Splitting of the longitudinal Néel transition in erbium in a -axis magnetic field

We have examined the magnetic phase diagram of single-crystal erbium in the temperature range between 60 K and 90 K and in applied magnetic fields along the c-axis up to 5.5 T using resistance versus temperature and magnetoresistance measurements. The H - T phase diagram for that region is presented. We have observed a splitting of the longitudinal Néel transition near 1.6 T. We have found a new phase with unknown structure in that portion of the phase diagram created by the splitting of the Néel transition. We have also found a multicritical point (P) at an applied field of 2.65 T and 71 K. A set of five magnetic phase lines appears to meet at this multicritical point.

Magnetic transitions in single-crystal erbium

Commensurate spin slip structures were observed by Gibbs et al. in X-ray scattering studies. We have observed magnetic transitions in macroscopic measurements of magnetization, AC susceptibility, electrical resistivity, and thermal expansivity along the three crystal axes of single-crystal erbium that correspond to these spin slip structures. Our measurements show antiferromagnetic ordering of the c axis and basal plane components at TN//=89 K and TN perpendicular to =53 K, respectively, as well as ferromagnetic ordering along the c axis below 18 K. In addition, we observe anomalies at 27, 29, 34, 40 and 51 K. These anomalies correspond well with previous studies. The order of these transitions can be determined using thermal expansion data. We observe anomalies at 21.6 K and 23.3 K that we believe correspond to basal plane recording in the 2(44) magnetic phase. There are also anomalies above TN perpendicular to suggesting a short-range ordering of the basal plane moments. We have analysed the resistivity versus temperature plot in the ferromagnetic region to determine the temperature dependence and the spin wave activation energy along the b and c axes.

Phase diagram (T, H) investigation by direct measurement of dR/dT in a magnetic material

The temperature dependences of the resistance R(T) and the singular part of near the critical regime and in the presence of magnetic fields H (0-5 T) are presented in this paper. The measurements were carried out using a novel technique from which ~~i)~ can be determined directly. This quantity, being related to the transport coefficient ( j~i, is directly connected to the specific heat behavior near the phase transition. The high accuracy of our experimental data allows us to compare the critical exponents deduced from our previous mea- surements in zero field (H = 0 T) and those predicted by several models of the renormal12ation group theory. We present a complete phase diagram for a single crystal of erbium oriented along the c-axis- This constitutes the first systematic study of field-induced magnetic phase transitions using the magnetoresistance R(T, NJ and its derivative ~ji( ~ near the critical points.

Magnetoelastic effects in single-crystal erbium

The authors have measured the ultrasonic elastic constants C33, C44, C11 and C66 and their associated attenuation coefficients ( alpha ij) for a single crystal of erbium as a function of temperature. They have observed anomalous behaviour in both Cij and alpha ij which they attribute to commensurate spin-slip structures as observed by Gibbs et al. and Lin et al. using synchrotron X-ray scattering and neutron diffraction techniques.

Critical exponents and amplitude ratio by direct measurement of dR/dT in erbium.

High-precision data of the electrical-resistance temperature derivative dR/dT along the c axis of a single crystal of erbium have been obtained using a direct measurement method. Numerical analysis of the dR/dT data for this helical antiferromagnet system provides a quantitative verification of the theory of scattering of electrons by spin fluctuations in the vicinity of the N\'eel temperature ${\mathit{T}}_{\mathit{N}}$ in a single crystal of Er. In addition, the accuracy of the present results enabled us to check the agreement between our results and the theoretical predictions of critical exponents and amplitude ratio obtained by renormalization-group (\ensuremath{\epsilon}-expansion and field-theoretical) methods. The results can be well described using the mean-field theory far from the critical region and above ${\mathit{T}}_{\mathit{N}}$. However, below ${\mathit{T}}_{\mathit{N}}$ and far from the transition region, an exponential law is suggested.

Effect of spin slip structures on the resistivity of erbium and holmium

Single-crystal erbium and holmium each have a series of magnetic phases which have become known as ‘spin slip’ structures. These structures were first observed using X-ray and neutron diffraction by Gibbs et al. Recently the present authors reported anomalies in the temperature dependence of the magnetization of single crystals of holmium and erbium. These anomalies correspond well with the results of Gibbs et al. In this paper the results of resistivity as a function of temperature for pure single crystals of erbium and holmium are reported. In single-crystal erbium, transitions in resistivity are seen at T = 19, 25, 30, 33, 40, 50, 53 and 86 K. Resistivity data for holmium clearly show transitions at T c = 13, 20, 24 and 42 K and T N = 132 K. In addition, a large increase in the electrical noise for holmium in the temperature range 80–105 K is observed. These electrical measurements are the first reported for erbium and holmium to show the effects of spin slip structures on resistivity.

Spin-slip transitions in erbium induced by a magnetic field

NGR studies ( 119Sn) and measurements of the magnetization of single crystal erbium revealed an interrelation between the cone angle of the magnetic moments and the spin-slip states in the basal plane. The obtained data are used to identify these states. The proof is presented for the first time that the hyperfine fields on nuclei of a nonmagnetic impurity in rare earth metals (REM) are produced in the regions with the smallest radii (of the order of interplanar distance). It is found that the transitions between commensurable magnetic structures can be caused not only by temperature but also by a magnetic field.

Magnetization of single-crystal erbium.

We present the results of magnetization and ac-susceptibility measurements on single-crystal erbium along all three crystal axes. We observe antiferromagnetic ordering of the {ital c} axis and the basal-plane-moment components at 89 and 53 K, respectively. In addition, we observe anomalies at 51, 40, 34, 29, and 27 K. These anomalies in magnetization and ac-susceptibility data correspond to the commensurate spin-slip structures observed by Gibbs {ital et} {ital al}. in x-ray synchrotron scattering studies. In addition, we find that the basal-plane ordering at {ital T}{sub {ital N}{perpendicular}}=53 K takes place before any spin-slip transition appears as the temperature is lowered.

On magnetic first-order transitions in erbium

The magnetic transitions in a single crystal of erbium have been investigated with a high-resolution scanning microcalorimeter. The transition between the ferro- and antiferromagnetic states takes place at 19.2 K (Tc) and is of first order with a latent heat of 18.5+or-1.0 J mol-1. In the antiferromagnetic state between Tc and 51 K four small energy peaks were observed which are ascribed to commensurate transitions. These transitions exhibit hysteresis effects and are of first order. At 53.4 K a relatively localised energy peak of 1.3+or-0.3 J mol-1 was found which probably arises from the ordering of the basal-plane moments. Also this transition was found to have a temperature hysteresis and is of first-order type. The antiferro-paramagnetic transition occurs at 85.6 K in this sample and its second-order nature is confirmed.