1 Introduction ................................................. l
References ................................................... 7
2 Experimental techniques of luminescence spectroscopy ......... 9
2.1 Emission and excitation spectra ......................... 9
2.2 Types of photodetectors ................................ 15
2.3 Monochromators and spectrographs ....................... 31
2.3.1 Dispersion and resolving power .................. 33
2.3.2 Throughput of monochromators and spectrographs .. 40
2.4 Signal detection methods in luminescence spectroscopy .. 44
2.4.1 Phase-synchronous detection ..................... 44
2.4.2 Photon counting ................................. 48
2.5 Signal-to-noise ratio in a scanning monochromator ...... 53
2.6 Fourier luminescence spectroscopy ...................... 57
2.7 Spectral corrections ................................... 58
2.8 Influence of slit opening on the shape of emission
spectra ................................................ 63
2.9 Time-resolved luminescence measurements ................ 67
2.9.1 Direct imaging of the luminescence response ..... 68
2.9.2 Phase-shift method .............................. 70
2.9.3 Time-correlated photon counting ................. 72
2.9.4 Boxcar integrator ............................... 73
2.9.5 Streak camera ................................... 76
2.10 Problems ............................................... 78
References .................................................. 80
3 Kinetic description of luminescence processes ............... 82
3.1 Radiative and non-radiative recombination.
Luminescence quantum yield ............................. 82
3.2 Monomolecular process .................................. 85
3.3 Bimolecular process .................................... 87
3.4 Stretched exponential .................................. 89
3.5 Multiple processes present simultaneously .............. 91
3.6 Problems ............................................... 96
References .................................................. 96
4 Phonons and their participation in optical phenomena ........ 98
4.1 Lattice vibrations - phonons ........................... 98
4.2 Electron-phonon and exciton-phonon interactions ....... 103
4.3 Lattice vibrations associated with point defects ...... 110
4.4 A localized optical centre in a solid matrix - the
configurational coordinate model ...................... 112
4.5 The shape of absorption and emission spectra of a
localized centre ...................................... 116
4.6 Thermal quenching of luminescence ..................... 120
4.7 Problems .............................................. 121
References ................................................. 122
5 Channels of radiative recombination in semiconductors ...... 123
5.1 Overview of luminescence processes in crystalline
semiconductors ........................................ 123
5.2 Recombination of free electron-hole pairs ............. 124
5.2.1 Direct bandgap ................................. 125
5.2.2 Indirect bandgap ............................... 128
5.3 Recombination of a free electron with a neutral
acceptor (e-A0) and of a free hole with a neutral
donor (h-D0) .......................................... 132
5.4 Recombination of donor-acceptor pairs (D0-A0) ......... 135
5.5 Luminescence excited by two-photon absorption ......... 139
5.6 Luminescence from transition metal and rare earth
ion impurities ........................................ 144
5.7 Problems .............................................. 146
References ................................................. 147
6 Non-radiative recombination ................................ 148
6.1 Transformation of the excitation energy into heat ..... 149
6.1.1 Multiphonon recombination ...................... 149
6.1.2 Auger and bimolecular recombination ............ 153
6.2 Creation of lattice defects ........................... 157
6.3 Photochemical changes ................................. 158
6.4 Problems .............................................. 159
References ................................................. 160
7 Luminescence of excitons ................................... 161
7.1 Concept of the Wannier exciton ........................ 162
7.1.1 Absorption spectrum of the Wannier exciton ..... 165
7.1.2 Direct bandgap: resonant luminescence of free
exciton-polaritons ............................. 168
7.1.3 Direct bandgap: luminescence of free excitons
with emission of optical phonons ............... 171
7.1.4 Luminescence of free excitons in indirect-
bandgap semiconductors ......................... 177
7.2 Bound excitons ........................................ 180
7.2.1 Excitons bound to shallow impurities ........... 182
7.2.2 Quantitative luminescence analysis of shallow
impurities in silicon .......................... 190
7.2.3 Excitons bound to isoelectronic impurities ..... 194
7.2.4 Self-trapped excitons .......................... 199
7.3 Problems ............................................... 201
References ................................................. 202
8 Highly excited semiconductors .............................. 205
8.1 Experimental considerations ........................... 206
8.2 Excitonic molecule or biexciton ....................... 207
8.2.1 Identification of the EM emission line ......... 208
8.2.2 Determination of biexciton parameters .......... 216
8.3 Collisions of free excitons ........................... 218
8.4 Electron-hole liquid (EHL)............................. 220
8.4.1 Luminescence determination of EHL parameters ... 223
8.4.2 Identification of the EHL emission band ........ 226
8.4.3 Coexistence of excitonic molecules with
electron-hole liquid ........................... 228
8.5 Electron-hole plasma (EHP) ............................ 230
8.5.1 Mott transition ................................ 230
8.5.2 Luminescence of EHP ............................ 232
8.6 Bose-Einstein condensation of excitons ................ 234
8.6.1 Properties of the Bose-Einstein distribution ... 234
8.6.2 Luminescence experiment: Bose-Einstein
condensation yes or no? ........................ 236
8.7 Problems .............................................. 239
References ................................................. 240
9 Luminescence of disordered semiconductors .................. 242
9.1 Densities of states in bands .......................... 242
9.2 Temperature dependence of luminescence ................ 244
9.3 Distribution of luminescence lifetimes ................ 248
9.4 Spectral shape of the emission band ................... 250
9.5 Some other properties of luminescence of disordered
semiconductors ........................................ 255
9.5.1 Correlation effects ............................ 255
9.5.2 Non-radiative recombination .................... 256
9.5.3 Luminescence of impurities and defects ......... 258
9.5.4 Luminescence 'fatigue' ......................... 260
9.6 Problems .............................................. 261
References ................................................. 262
10 Stimulated emission ........................................ 263
10.1 Spontaneous versus stimulated emission. Optical
gain .................................................. 263
10.2 Optical gain in semiconductors ........................ 267
10.3 Spectral shape of the optical gain .................... 271
10.4 Stimulated emission in an indirect-bandgap
semiconductor ......................................... 278
10.5 Participation of excitons in stimulated emission ...... 282
10.6 Experimental techniques for measuring the optical
gain .................................................. 287
10.6.1 Variable stripe length (VSL) technique ......... 287
10.6.2 Pump and probe (P&P) method .................... 295
10.7 Problems .............................................. 299
References ................................................. 300
11 Electroluminescence ........................................ 302
11.1 Historical notes ...................................... 302
11.2 High-field electroluminescence ........................ 304
11.2.1 Experimental considerations .................... 304
11.2.2 Mechanisms of high-field electroluminescence ... 308
11.2.3 Intensity, spectral and temporal
characteristics ................................ 316
11.3 Injection electroluminescence ......................... 321
11.3.1 Electrical properties of a p-n junction ........ 322
11.3.2 Intensity, spectral and temporal
characteristics of LEDs ........................ 327
11.4 Electroluminescence of a p-n junction biased in the
reverse direction ..................................... 333
11.5 Problems .............................................. 336
References ................................................. 337
12 Electronic structure and luminescence of low-dimensional
semiconductors ............................................. 339
12.1 Basic types of low-dimensional semiconductors ......... 340
12.1.1 Semiconductor heterostructures ................. 340
12.1.2 Basic types of quantum-well heterostructures ... 342
12.2 Density of states in low-dimensional semiconductors ... 344
12.3 Quantum wells (layers)—two-dimensional
semiconductors ........................................ 347
12.3.1 Single quantum well with infinite barriers ..... 347
12.3.2 Quantum well with finite barriers .............. 351
12.3.3 Excitons in a quantum well ..................... 353
12.3.4 Optical transitions in a quantum well .......... 355
12.3.5 Luminescence of quantum wells .................. 357
12.4 Quantum wires ......................................... 359
12.5 Quantum dots - nanocrystals ........................... 363
12.5.1 Quantum dot with spherically symmetric
potential ...................................... 363
12.5.2 Types of quantum dots according to the
strength of the quantum confinement effect ..... 365
12.5.3 Luminescence of quantum dots ................... 368
12.6 Exciton-phonon interaction. Phonon bottleneck ......... 371
12.7 Some special phenomena ................................ 374
12.8 Problems .............................................. 378
References ................................................. 379
13 Effects of high excitation in low-dimensional structures ... 381
13.1 Excitonic molecule (biexciton) in a quantum well ...... 382
13.2 Trions in a quantum well .............................. 384
13.3 Collisions of free excitons in a quantum well ......... 386
13.4 Electron-hole plasma (EHP) and electron-hole liquid
(EHL) in 2D structures ................................ 387
13.5 Biexcitons, EHP, and EHL in quantum wires ............. 392
13.6 Effects of high excitation in quantum dots
(nanocrystals) ........................................ 395
13.7 Problems .............................................. 398
References ................................................. 399
14 Stimulated emission and losing in low-dimensional
structures ................................................. 400
14.1 Stimulated emission in quantum wells .................. 400
14.1.1 Localized excitons ............................. 401
14.1.2 Radiative decay of an exciton with emission
of an LO-phonon (X-LO) ......................... 404
14.1.3 Stimulated emission in electron-hole plasma
(EHP) .......................................... 405
14.2 Stimulated emission in quantum wires .................. 408
14.3 Stimulated emission in nanocrystals ................... 410
14.3.1 Nanocrystals dispersed in a matrix ............. 410
14.3.2 Heterostructures with ordered quantum dots ..... 416
14.4 Random lasing ......................................... 418
14.5 Problems .............................................. 420
References ................................................. 421
15 Silicon nanophotonics ...................................... 423
15.1 Silicon nanocrystals .................................. 424
15.2 Optical gain in silicon nanocrystals .................. 426
15.3 Active planar waveguides made of silicon
nanocrystals .......................................... 428
15.4 Electroluminescence of silicon nanocrystals ........... 431
15.5 Silicon nanocrystals combined with Er3+ ions .......... 434
15.6 Biological applications of silicon nanocrystals ....... 437
15.7 Problems .............................................. 438
References ................................................. 439
16 Photonic structures ........................................ 441
16.1 Photonic crystals ..................................... 441
16.1.1 Spontaneous emission ........................... 443
16.1.2 Stimulated emission ............................ 446
16.2 Microresonators ....................................... 447
16.3 Microcavities ......................................... 449
16.4 Single photon sources ................................. 451
16.5 Problems .............................................. 453
References ................................................. 454
17 Spectroscopy of single semiconductor nanocrystals .......... 455
17.1 Basic principles ...................................... 456
17.2 Experimental techniques ............................... 457
17.2.1 Wide-field micro-spectroscopy .................. 458
17.2.2 Scanning techniques ............................ 460
17.3 Preparation of samples ................................ 465
17.3.1 Electron-and ion-beam lithography .............. 465
17.3.2 Colloidal dispersions .......................... 466
17.4 Experimental observation of luminescence from
individual nanocrystals ............................... 467
17.4.1 Hidden fine structure of luminescence spectra .. 467
17.4.2 Changes in spectra: jumps, shifts, blinking .... 469
17.4.3 Stark effect ................................... 470
17.4.4 Luminescence polarization ...................... 472
17.4.5 Luminescence intermittency - blinking .......... 478
17.5 Nanocrystals as sources of non-classical photon flux .. 485
17.5.1 Measuring photon statistics .................... 485
17.5.2 Experimental manifestation of non-classical
light emitted by a single nanocrystal .......... 487
17.6 Problems .............................................. 490
References ................................................. 491
Appendices .................................................... 493
A Convolution ............................................. 493
В Emission spectrum of free excitons including phonon
broadening .............................................. 495
С Luminescence of an excitonic molecule ................... 497
D Kinetic model of exciton condensation ................... 502
E Bose-Einstein condensation .............................. 503
F Emission band due to strong electron-phonon
interaction ............................................. 505
G Fitting the optical gain spectral shape in the model
of k-relaxation ......................................... 507
H Reabsorption of luminescence in semiconductors .......... 511
I Oscillator strength ..................................... 513
J Fitting with a double exponential (Kocka's summation) ... 514
К Absolute quantum yield of luminescent materials ......... 515
L Basic description of statistics of light from
classical and non-classical sources ..................... 521
M Behaviour of multi-component spectral mixtures: the
isostilbic point ........................................ 526
Subject index ................................................. 530
Material index ................................................ 538
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