Erbium doped materials are of great interest in thin film integrated optoelectronic technology, due to their Er3+ intra-4f emission at 1.54 μm, a standard telecommunication wavelength. Er-doped dielectric thin films can be used to fabricate planar optical amplifiers or lasers that can be integrated with other devices on the same chip. Semiconductors, such as silicon, can also be doped with erbium. In this case the Er may be excited through optically or electrically generated charge carriers. Er-doped Si light-emitting diodes may find applications in Si-based optoelectronic circuits. In this article, the synthesis, characterization, and application of several different Er-doped thin film photonic materials is described. It focuses on oxide glasses (pure SiO2, phosphosilicate, borosilicate, and soda-lime glasses), ceramic thin films (Al2O3, Y2O3, LiNbO3), and amorphous and crystalline silicon, all doped with Er by ion implantation. MeV ion implantation is a technique that is ideally suited to dope these materials with Er as the ion range corresponds to the typical micron dimensions of these optical materials. The role of implantation defects, the effect of annealing, concentration dependent effects, and optical activation are discussed and compared for the various materials.

Erbium implanted thin film photonic materials

Second-generation TiO2-xDx photocatalysts doped with either anions (N, C, and S mostly) or cations have recently been shown to have their absorption edge red-shifted to lower energies (longer wavelengths), thus enhancing photonic efficiencies of photoassisted surface redox reactions. Some of the studies have proposed that this red-shift is caused by a narrowing of the band gap of pristine TiO2 (e.g., anatase, Ebg = 3.2 eV; absorption edge ca. 387 nm), while others have suggested the appearance of intragap localized states of the dopants. By contrast, a recent study by Kuznetsov and Serpone (J. Phys. Chem. B, in press) has proposed that the commonality in all these doped titanias rests with formation of oxygen vacancies and the advent of color centers (e.g., F, F+, F++, and Ti3+) that absorb the visible light radiation. This article reexamines the various claims and argues that the red-shift of the absorption edge is in fact due to formation of the color centers, and that while band gap narrowing is not an...

Is the Band Gap of Pristine TiO2 Narrowed by Anion- and Cation-Doping of Titanium Dioxide in Second-Generation Photocatalysts?

Nonlinear Optical Crystals: A Complete Survey

The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point‐charge model and p‐d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational‐electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal‐field parameters have been calculated as convergent lattice sums. The observed trigonal‐field parameter has the opposite sign from that calculated by the point‐charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 A displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.

Optical spectra of transition-metal ions in corundum

Defects in LiNbO3—I. experimental aspects

The energy transfer between and ions in lithium niobate is investigated and modelled using the rate equation formalism. An efficient energy transfer from to is found and the transfer and back-transfer coefficients have been determined ( and , respectively). Using the rate equation formalism it is shown that population inversion of the level (upper laser level at ) is attainable at sufficiently low pumping levels, making this material suitable for laser applications. The effective transfer efficiency is also calculated, showing good agreement with the experimental values obtained from the increase of the emission.

http://iopscience.iop.org/article/10.1088/0953-8984/10/39/023/pdf

Yb3+ to Er3+ energy transfer in LiNbO3

The laser performance of the nonlinear Yb3+:MgO:LiNbO3 crystal is assessed under Ti:sapphire laser pumping. Spectral properties related to infrared laser action such as the emission and absorption cross sections have been evaluated. Different crystallographic configurations have been used. Laser oscillation in the near infrared region has been observed along the crystallographic c axis and along the type I phase matching direction for infrared to green generation. High slope efficiency in the infrared region (62%) and the possibility of low laser thresholds (14.7 mW) are demonstrated. By using a birefringent filter, broadband tuning from 1030 to 1070 nm is obtained in this system. In addition, 58 mW of green power by self-frequency doubling of infrared laser emission is achieved, revealing the potential of LiNbO3:MgO as a self-frequency-doubling material.

Continuous wave infrared laser action, self-frequency doubling, and tunability of Yb3+:MgO:LiNbO3

Growth of LiNbO3 co-doped with Er3+/Yb3+

The influence of ${\mathrm{LiNbO}}_{3}$ stoichiometry ([Li]/[Nb] ratio) on a number of physical phenomena, related to the presence of lattice defects, has been investigated. Positron-lifetime spectra from crystals with different compositions reveal two states for positrons (lifetimes of 230 and 250 ps). The long-lived state is attributed to positrons trapped at cation vacancies, most likely Nb vacancies. Luminescence spectra under x-ray excitation show the same main emission band, peaking at about 2.9 eV for all compositions, although the yield is drastically reduced on increasing Li deficiency. The optical-absorption spectra induced by x-ray irradiation at 80 K is a broad, structured band that can be decomposed into three components peaked at about 1.6, 2.3, and 3.3 eV, for all stoichiometries. However, the production efficiency of each component is dependent on composition. Crystals reduced by heating in a vacuum show a complex optical-absorption spectrum that can be decomposed in two main Gaussian components peaked at about 3.2 and 2.6 eV, with some contribution of another band at about 1.6 eV. The amount of reduction, as measured by the induced absorption, markedly increases with Li deficiency.

Influence of stoichiometry on defect-related phenomena in LiNbO3.

The lattice location of Fe in LiNbO3 single crystals has been investigated by PIXE-channelling techniques. For the first time, it has unambiguously shown that Fe (mostly as Fe3+) lies at or near the Li-site, although a small fraction sitting at the Nb or intrinsic vacant sites cannot be ruled out.

https://iopscience.iop.org/article/10.1209/0295-5075/14/6/010/pdf

J.A. Sanz-García

Papers

Yb3+ to Er3+ energy transfer in LiNbO3

Continuous wave infrared laser action, self-frequency doubling, and tunability of Yb3+:MgO:LiNbO3

Growth of LiNbO3 co-doped with Er3+/Yb3+

Influence of stoichiometry on defect-related phenomena in LiNbO3.

Lattice Site of Iron in LiNbO3(Fe3+) by the PIXE/Channelling Technique