Luminescence. Application of luminescence. Dental application. Physical basis of dental material science 11. Optical and other properties.

Transcription

1 Luminescence Light emission over the thermal radiation. Light emission after excitation. e.g. atom E 1 Light emission: hn = E 1 E 0 E 0 Excitation: energy uptake by the electron E 0 ground state E 1 excited state Physical basis of dental material science 11. Optical and other properties. Summary 1 2 Application of luminescence Dental application excitation name: -luminescence example light photo- quinine-sulphate, phosphor, X-ray X-ray NaI(Tl) radioactive radio- NaI(Tl) radiation electric field electro- mercury-lamps mechanical effect tribo- sugarcube chemical raction chemo- (bio-) firebug heat thermo- CaSO4(Dy) + materials analysis, structure of biological macromolecules, fluorescence microscopy, sensors, monitors, radiation detectors,

2 energy Electronic states Life-time (t): time while the intensity decreases by factor e. emission spectrum: J() (Intensity of the emitted light versus wavelength) Jablonski diagram: internal conversion vibrational relaxation S energy state of electrons singlett states (S 0 ground state) T energy state of electrons triplett states arrows - spin line/band spectrum J J 0 J 0 e t J J 0 e t t t fluorescein Stokes s shift: t fluo t phos phos fluo abs excitation fluorescence phosphorescence Quantum efficiency (Q): no.of emitted photons Q (energy abs fluo phos no.of absorbed photons light emission absorption) luminescence 6 transparent - translucent - opaque Optical properties fluorescence after absorption color 3 Color Hue: refers to a pure color Saturation: perceived intensity of a specific color. color space : 3 coordinates primary color chromatic color color mixed color achromatic color translucent: diffuse transparency Depends on the spectrum of the incident light! additive substractive 1, 3, 5 2, 4, 6 1 red 2 yellow 3 green 4 cyan 5 blue 6 magenta white, gray, black primary color: sets of colors that can be combined to make a color. additive color model: involves light emitted directly from a source. opaque: not transparent, diffuse reflection color 2 opalescence substractive color model : mixing of paints, dyes, inks, and natural colorants. color 1 7 regular units: hue: saturation: % 8 2

3 Electric properties Electric charges in materials: electrons, ions. Electric properties Q charge, unit: C (coulomb) Resistivity (): - (specific resistance) material s (S/m) F E Q R A l R: resistance A: cross-section l: length unit: Wm silver gold platinum germanium 2.2 silicon hyacinth conductors semiconductors Coulomb-force: attractive or repulsive E: strength of the electric field = F/Q Work: W AB F s QE s current (I): flow of charges. (due to the electric field) unit: amper (A) Q I t Conductivity (s): 1 s unit: (Wm) 1 = S/m porcelain glass PMMA PE insulators Voltage (V): unit: volt (V) V AB W Q AB Ohm s law: U R I R: resistance, unit: ohm (W) 9 S: siemens, unit of conductance conductance = 1/R 10 Chemical properties Corrosion is the disintegration of a material into its constituent atoms due to chemical reactions. Type of corrosion Oxidation and corrosion of metals M M n n e in acidic medium O2 4H 4e 2H2O Galvanic corrosion: one metal corrodes to another when both metals are in electrical contact and immersed in an electrolyte. galvanic series of elements (in salt water) neutral or alkaline medium O2 2 2H O 4e 4 OH ) Pt Au Ti Ag Cu Ni Sn Pb Al Zn inert active metal (M) medium metal (M) medium metal (M) medium corrosion of the amalgam 11 crevice corrosion: is a corrosion occurring in spaces to which the access of the working fluid from the environment is limited. p. 643 corrosion of the amalgam 12 3

4 Typical amalgam Corrosion of ceramics typical constitution metal weight% Ag Sn Cu 0-6 Zn 0-2 Hg Hg H 2 O dissolution increasing crack ( static fatigue ) Degradation of the polimers Comparison of the properties of the materials water uptake (alcohol) swelling, dissolution weaker bonds changing mechanical and optical properties UV irradiation ionization breaking covalent bonds strand breaks, crossing-over,

5 17 18 Metals Increasing the strength of the metals properties in general: high density stiff strong ductile (plastic) tough (tough fracture) hard thermal conductor electric conductor opaque, metal color corrosive 19 grain size (d) decreasing Motion of dislocations! 20 5

6 Cold metal-work strong moderate metal-work 0 Alloying: one metal with other metal(s) or non-metal(s) often enhances its properties Ceramics properties in general: medium density rigid strong (in rupture medium) not plastic brittle (brittle fracture) hard thermal insulator weak thermal shock tolerancy electric insulator different optical properties low chemical corrosion 23 Crack sensitivity s tension s compressio n 24 6

7 Crack types Polimers properties in general: low density elastic weak ductile medium tough - brittle soft viscoelastic thermal insulator electric insulator different optical properties degradation High variety of properties Important factors temperature degree of crystallinity brittle (e.g. PMMA) PMMA plastic (e.g. PE) elastic (elastomeric) e.g. rubber 1 = amorphous polymer 2 = amorphous polymer, high molecular weight 3 = crystalline polyme 4 = crystalline polymer, higher degree of crystallinity molecular weight typical polymer

8 Composites in dentistry properties in general: low and medium density medium stiff - elastic strong ductile tough hard medium hard thermal insulator electric insulator different optical properties small degradation carbon nanotubes (CNT) Combination of advantageous properties Composite: rubber (SMR) + carbon nanotubes (CNT) rubber (SMR CV60) Effect on properties 31 8