Effect of mechanical load on optical properties of un-doped and Eu3+-doped Y2SiO5 at the quantum scale

It is well known that material properties are size dependent at small enough geometrical scales. With the advance of technology and computational power, we are now able to bridge the atomistic or even electronic scale phenomena with macroscopic properties of materials. A strategy to capture the electronic structure effect is to perform first principles calculations.
Here we present results of first principle calculations that show the effects of mechanical strains on the optical resonance shift in Y2SiO5 and Eu-doped Y2SiO5. The corresponding simulations are conducted using the open source software known as Quantum Espresso. The unit cell is monoclinic and it contains eight basic molecules of Y2SiO5. However, due to symmetry we can reduce the unit cell to its primitive cell that contains only four basic molecules and, hence, reduce computational cost of the system. Furthermore, since many spectroscopic phenomena take place when the host is doped with one of the Rare Earth Elements (REE) the host is in this case doped with Europium (Eu). In this paper 2 of the 16 Yttrium atoms are replaced with Eu, which corresponds to 12.5% doping. First, the unit cell is optimized geometrically with a mathematical algorithm to find the minimum energy state of the system. Then, a perturbation is introduced to the system to excite electrons, while the unit cell undergoes mechanical loading. The results exhibit the shift in absorbance frequency due to doping of the host material by the REE ions, as well as the variation of frequency due to axial loads in both doped and un-doped systems that suggest anisotropy of the absorption spectrum in response to mechanical loads. Finally, we have also observed the dependence of applied force direction on the crystal through comparison of compressive and tensile effects.