Physical Basis of Spectroscopy: Electrical Properties, Absorption, and Spectrometry

Comprehensive vocabulary flashcards covering the physical basis of spectroscopy, including semiconductor physics, dielectric polarization, electrical dispersion in biological tissues, the Beer-Lambert law, and molecular luminescence mechanisms.

Semiconductor

A solid body characterized in band structure theory by a small band gap ($< 2\,eV$) between the valence band and conduction band, allowing electrons to be easily transferred to the conduction band at elevated temperatures or by electromagnetic or corpuscular radiation.

Intrinsic conductance

The conduction of electricity occurring in a pure semiconductor crystal (such as pure germanium) containing an equal number of free conduction band electrons and valence band holes.

Type n semiconductor

A semiconductor doped with an electron donor element from the 5th group of the periodic table, providing an additional electron per incorporated atom so that negative electrons become the major charge carriers.

Type p semiconductor

A semiconductor doped with an electron acceptor element from the 3rd group of the periodic table, creating free holes in the valence band that serve as the major charge carriers.

Conductors of the first kind

Solids (such as metals) exhibiting electron conductance, in which the valence band overlaps the conduction band such that the energy band gap equals zero, allowing electrons to move under an arbitrarily small electric field.

Conductors of the second kind

Substances (including electrolytes, aqueous solutions of acids, bases, salts, and molten alkaline salts) in which electrical current is carried by mobile positive and negative ions, causing physical and chemical changes in the medium.

Dielectric

A non-conducting material (insulator) with an energy band gap greater than $2\,eV$ that contains permanent or electric field-induced dipoles that realign when placed in an external electric field.

Electron polarization

A dielectric phenomenon where the geometrical center of negative charges of an atom's electron shell shifts relative to the positive nucleus under an applied electric field, inducing an electric dipole without shifting the atom's position.

Deformation polarization

The polarization mechanism in molecular dielectrics where an external electric field induces dipoles by shifting deformed atoms within the molecules.

Orientation polarization

The polarization occurring in molecules with stable, permanent electric dipoles, where an external electric field exerts a torque that rotates and aligns the dipoles along the field lines.

Ionic polarization

A polarization effect observed when free ions within a confined space (such as a plant or animal cell) displace to opposite ends under an electric field, turning the entire cell into a large electric dipole.

Vector of polarization ($\vec{P}$)

A macroscopic measure of the total polarization of a dielectric, defined as the vector sum of all electric dipole moments divided by the dielectric volume ($\vec{P} = \frac{\sum \vec{p}_e}{\Delta V}$), with units of $\text{C/m}^2$.

Conductance losses

Energy dissipation in a real dielectric where the electric field energy in a charged capacitor is converted into heat due to the flow of residual free charges through the material.

Dielectric losses

Energy dissipation observed in a capacitor when an alternating electric field of high frequency causes rapid rotation and friction of electric dipoles within a viscous medium.

Impedance ($Z$)

The total resultant opposition of a biological tissue or electrical circuit to alternating current, combining real ohmic resistance ($R$) and capacitive reactance.

Equivalent electrical circuit of a cell or tissue

A circuit model used to simulate electrical currents in living organisms, where $R_m$ and $C_m$ represent membrane resistance and capacitance, $R_i$ represents cytoplasm resistance, and $R_p$ represents extracellular fluid resistance.

Dispersion of electrical conductivity and permittivity

The frequency dependence of the electrical conductivity and permittivity of biological tissues, caused by ions and dipoles failing to keep pace with changing alternating electric fields at higher frequencies.

$\alpha$-dispersion

The low-frequency dispersion range observed from several $\text{Hz}$ to several $\text{kHz}$ (mean relaxation frequency $f_0 \approx 100\,Hz$ in muscle tissue) connected to macroscopic cell polarization, where $f_0$ is approximately linearly related to cell radius.

$\beta$-dispersion

The dispersion range extending from several dozen $\text{kHz}$ to approximately $30\,MHz$ (mean relaxation frequency $f_0 \approx 1\,MHz$) originating from the nonhomogeneous structure of tissues and the electrical properties of cell membranes.

$\gamma$-dispersion

The ultra-high-frequency dispersion range associated with dipole relaxations of subcellular structures, biomolecules, and bounded water ($10^2 \div 10^3\,MHz$) as well as free water (several dozen $\text{GHz}$).

Lambert law

The optical law stating that parallel mono-energetic radiation passing through an absorbing medium is attenuated exponentially according to $P_D = P_0 e^{-kd}$, where $P_0$ is incident power, $P_D$ is transmitted power, $d$ is layer thickness, and $k$ is the attenuation coefficient.

Beer's law

The principle stating that for low-concentration solutions of completely ionized or non-ionized solutes, the attenuation coefficient $k$ is directly proportional to the solution concentration: $k = a_\lambda \cdot c$.

Beer-Lambert law

The combined mathematical relationship governing radiation absorption: $P_D = P_0 e^{-a_\lambda c d}$, relating transmitted radiation power ($P_D$) to incident power ($P_0$), extinction coefficient ($a_\lambda$), concentration ($c$), and layer thickness ($d$).

Permeability ($\tau_s$)

The ratio of transmitted radiation power through a solution ($P_D$) to the radiation power transmitted through the pure solvent ($P_{Do}$), expressed as $\tau_s = \frac{P_D}{P_{Do}}$.

Absorption ($A$)

A parameter that depends linearly on solute concentration, defined mathematically as $A = -\ln(\tau_s) = a_\lambda c d$.

Photoelectric absorptiometer

An optical measuring device comprising a light lamp ($Z$), collimator ($O$), cuvettes ($K_1$, $K_2$), color filter ($F$), iris ($L$), photovoltaic selenium cell ($S$), and meter ($M$), capable of determining solute concentrations with an error under $2\%$.

Photoluminescence

Cold, non-thermal light emission resulting from the excitation of atoms or molecules by photons of visible or ultraviolet radiation.

Fluorescence

A form of photoluminescence where an excited atom or molecule emits a photon and returns to the ground state within a time on the order of $10^{-8}\,s$ after photon absorption.

Phosphorescence

A type of photoluminescence where an excited molecule transitions via a non-radiative pathway into a metastable state ($T$) with an excited-state lifetime exceeding $10^{-8}\,s$ before radiatively returning to the ground state.

Resonant fluorescence

A luminescence process in which the energy of the emitted photon equals the energy of the absorbed excitation photon, occurring when no absorbed energy is lost to non-radiative transitions.

Stokes rule

The rule stating that the wavelength of excitation light ($\lambda_p$) stimulating luminescence is smaller than the wavelength of the emitted luminescence light ($\lambda_e$) because part of the absorbed energy is dissipated through collisions.

Emission spectrum

The characteristic spectral distribution of light emitted by thermally, electrically, or radiatively excited matter, appearing as a line spectrum for atomic gases, a band spectrum for molecular gases, or a continuous spectrum for liquids and solids.

Absorption spectrum

The spectrum produced when white radiation passes through a cooler substance, yielding a continuous spectrum punctuated by dark lines or bands corresponding to allowed quantum transitions of the absorbent.

Spectroscope

An optical device used to observe visible emission and absorption spectra, consisting of an entrance slit ($S$), collimator ($K$), dispersing prism ($P$), scale projector ($R$), and observation telescope ($L$).

Luminescence analysis

A highly sensitive analytical method based on characteristic luminescence radiation, allowing quantitative detection of test substances at concentrations down to $10^{-8}\,mol/l$ and masses on the order of $10^{-9}\,g$.