Novel two-dimensional (2D) materials with promising and tunable nonlinear optical (NLO) properties are desirable for the development of optoelectronic nanodevices. Here, the geometric structures, electronic properties, and nonlinear optical responses of graphene (GE), graphyne (GY), and graphdiyne (GDY) complexes with single adsorbed alkali metals (AM: Li, Na, K) were systematically investigated using density functional theory calculations. All the alkali metals are energetically preferred for interacting with the large triangular holes in extensively delocalized π-conjugated graphyne and graphdiyne via an intramolecular electron donor–acceptor (D-π-A) process and can be stabilized by van der Waals interactions. Moreover, AM@GY and AM@GDY (AM = Li, Na, K) exhibit dramatically higher structural stability than AM@GE owing to their high binding energies. The effects of doping alkali metal atoms into the surface of GDY on the electronic structures were investigated by an analysis of the HOMO–LUMO gap and density of states. The strong alkalide characteristics of these complexes can be demonstrated by their NBO charges and lower vertical ionization potentials (VIPs). In addition, the adsorption of alkali metals greatly increases the first hyperpolarizability (βtot), and AM@GDY possesses exceptionally high βtot values (8.57 × 104 to 3.93 × 105 a.u.) in comparison with AM@GE and AM@GY owing to its unique structural patterns. The frequency dependences of the electro-optical (EO) Pockels effect and second-harmonic generation (SHG) were analyzed in order to investigate the dynamic NLO process, and it was revealed that SHG resonance enhancement takes place at ω = 0.10 a.u. The present investigation not only highlights the importance of the adsorption of single alkali metals on the surface of GDY for enhancing its NLO properties but also indicates that AM@GDY complexes are potentially important materials for next-generation graphdiyne-based optoelectronics applications.

Investigations of electronic and nonlinear optical properties of single alkali metal adsorbed graphene, graphyne and graphdiyne systems by first-principles calculations

In this study, we designed a series of new alkali metal-adsorbed graphdiyne (GDY) structures (denoted as AM3@GDY (AM = Li, Na, K)) with an intramolecular electron donor–acceptor framework using density functional theory calculations. It is found that the three alkali metals are energetically preferred to be adsorbed on the three hollows of the largely delocalized π-conjugated GDY surface, while the adsorption of alkali metals largely affects the electronic properties of the complexes, and reduces the vertical ionization potentials. More interestingly, the doping of alkali metal atoms dramatically enhances the static first hyperpolarizabilities (βtot) of AM3@GDY, of which the K3@GDY cluster possesses a remarkably giant βtot value of ∼1.61 × 105 a.u., which is enough for it to exhibit strong nonlinear optical (NLO) behavior. These findings may provide new insights into the design of novel graphdiyne-based NLO materials and promote further potential applications in optoelectronic nanodevices.

Design of novel graphdiyne-based materials with large second-order nonlinear optical properties

We have developed a continuous-wave, lamp-pumped, intracavity frequency-doubled laser that provides as much as 13.5 W of power in the green, linearly polarized TEM00 output, and very low misalignment sensitivity. These results have been obtained with a Nd:YLF rod of large cross section, a lithium triborate frequency-doubling crystal, and a novel resonator design. We demonstrate that the problem of power fluctuations and chaos in this class of lasers (the green problem) can effectively be overcome and that fluctuations of less than ±1% on a millisecond time scale can be obtained.

Intracavity frequency doubling of a cw high-power TEM00 Nd:YLF laser.

Crystal growth, thermal and optical performance of BiB3O6

LiB3O5 crystal structure at 20, 227 and 377 °C

The anisotropic thermal expansion of LiB3O5 has been studied along the principal crystallographic directions over the temperature range of 17 to 790 degrees C by means of high-temperature X-ray powder diffraction. This orthorhombic crystal exhibits strongly anisotropic expansion with coefficients of 108.2*10-6 K-1 for (100), 33.6*10-6 K-1 for (010) and -88.0*10-6 K-1 for (001) at 50 degrees C. The coefficients tend to zero when the temperature approaches the crystal's peritectic reaction point.

https://iopscience.iop.org/article/10.1088/0022-3727/23/8/012/pdf

Anisotropic thermal expansion of LiB3O5

Thermal expansion of the low-temperature form of BaB{sub 2}O{sub 4} ({beta}-BaB{sub 2}O{sub 4}) crystal has been measured along the principal crystallographic directions over a temperature range of 9{degrees} to 874{degrees}C by means of high-temperature X-ray powder diffraction. This crystal belongs to the trigonal system and exhibits strongly anisotropic thermal expansions. The expansion along the c axis is from 12.720 to 13.214 {Angstrom} (1.2720 to 1.3214 nm), whereas it is from 12.531 to 12.578 {Angstrom} (1.2531 to 1.2578 nm) along the {alpha} axis. The expansions are nonlinear.

Lin Wei

Papers

Anisotropic thermal expansion of LiB3O5

Thermal Expansion of the Low-Temperature Form of BaB2O4