Solid State Chemistry : An Introduction to Crystal Structures

FMIPA UGM – November 2020

Prof. Dra. Wega Trisunaryanti, M.Si., Ph.D.EngDr.rer.nat Niko Prasetyo

Outline Solid state chemistry

12 chapters from crystal structures to nanoscience

Lecture and reading materials :

At this classroom

Ugm.id/1ND

Final exam

Open Book (not open google)

Do it by yourself!

Main reference :

Solid State Chemistry: An Introduction, Third Edition 3rd Edition by Lesley E. Smart (Author), Elaine A. Moore (Author)

Optical solid material

Laser (light amplification by stimulated emission of radiation)

Optical solid material

Light-emitting diodes (LEDs)

Optical solid material

Laser (light amplification by stimulated emission of radiation)

Of interest to the solid state chemist are two types of laser, typified by the ruby laser and the gallium arsenide laser.

Light-emitting diodes (LEDs) are used for displays including those on digital watches and scientific instruments.

Optical solid material

Chemistry behind the optical solid

When an atom absorbs a photon of light of the correct wavelength, it undergoes a transition to a higher energy level

The electron will only absorb the photon if the photon’s energy matches that of the energy difference between the initial and final electronic energy level, and if certain rules, known as selection rules, are obeyed

In light atoms, the electron cannot change its spin and its orbital angular momentum must change by one unit; in terms of quantum numbers ∆s=0, ∆l=±1

For a sodium atom, for example, the 3s electron can absorb one photon and go to the 3p level

The 3s electron will not, however, go to the 3d or 4s level

Optical solid material

Chemistry behind the optical solid

Optical solid material

Chemistry behind the optical solid

An electron that has been excited to a higher energy level will sooner or later return to the ground state

spontaneous emission

induced or stimulated emission

Let us take as an example an ion with one d electron outside a closed shell (Ti3+ for example). This will help us understand the ruby laser.

In a crystal, these levels are split; for example, if the ion occupied an octahedral holethe 3d levels would be split into a lower, triply degenerate (t2g ) level and a higher, doubly degenerate (eg) level

Optical solid material

Chemistry behind the optical solid

Ruby (Al2O

3 with 0.04 – 0.5 % of Cr3+)

The ions absorb light and go to states 3 and 4. They then undergo a radiationlesstransition to state 2

Because the probability of spontaneous emission for state 2 is low,and no convenient non-radiative route is available tothe ground state, a considerable population of state 2 can build up

When eventually (about 5 milliseconds later) someions in state 2 return to the ground state, the first few spontaneously emitted photons interact with other ions in state 2 and induce these to emit

The resulting photons will bein phase and travelling in the same direction as the spontaneously emitted photons andwill induce further emission as they travel through the ruby

The ruby is in a reflectingcavity so that the photons are reflected back into the crystal when they reach the edge

The reflected photons induce further emission and by this means, an appreciable beam ofcoherent light is built up

The mirror on one end can then be removed and a pulse of light emitted

One of the most important application of Laser in modern chemistry is the photochemistry

You can find the Indonesian version of this book in our univ library

Energy vs. crystal momentum for a semiconductor with an indirect band gap, showing that an electron cannot shift from the highest-energy state in the valence band (red) to the lowest-energy state in the conduction band (green) without a change in momentum

Energy vs. crystal momentum for a semiconductor with a direct band gap, showing that an electron can shift from the highest-energy state in the valence band (red) to the lowest-energy state in the conduction band (green) without a change in crystal momentum.

● Ti-doped GaN is likely to be a promising dilute magnetic semiconductor. So far, themechanism by which Ti impurity influences the electronic and optical properties of GaN NWs is still absent.

● DFT Calculations ; GGA PW91 ; Plane wave basis sets with cut off 400 Ry

● All calculations are carried in reciprocal space with Ga:3d104s24p1, N:2s22p3 , andTi:4s23d2 as the valence electrons

The conduction band and valence band of Ti-doped GaN NWs move towards the low energy region, and the Fermi level moves towards the conduction band, which result in the n-type GaN NWs

● PDOS calculations reveal that the valence band maximum of pure GaN nanowire comes from the N-2p orbital, while the conduction band minimum is ruled by the Ga-4s and N-2s orbital

● The energy levels of single Ti-doped GaN NWs are near the Fermi level, which are ruled by the Ga-4s, N-2s, and Ti-3d orbital

● Fig. 3(c) and (d) shows that the energy levels of pair and triple Ti-doped GaN NWs are near the Fermi level, which are ruled by the Ti-3d orbital.

The donor states of near the Fermi level are mainly formed by Ti 3d states, and Ti-doped GaN NWs' Fermi level has a upshift compared with pure GaN NWs

Terima kasih!