Under these circumstances, to establish a design principle of high-performance
organic light-emitting devices Yamao et al. [7] have developed a light-emitting
device where an organic crystal of P6T (see structural formula of Fig. 9.10a) was
placed onto a diffraction grating (Fig. 9.10b [7]). The compound P6T is known as
one of a family of thiophene/phenylene co-oligomers (TPCOs) together with BP1T,
AC5, AC’7, etc. that appear in Fig. 9.8 [10, 11]. The diffraction grating was
engraved using a focused ion beam (FIB) apparatus on an aluminum-doped zinc
oxide (AZO) substrate. The resulting substrate was then laminated with the thin
crystal of P6T (Fig. 9.10c). Using those devices, Yamao et al. excited the P6T crystal
with ultraviolet light of a mercury lamp and collected the emissions from the crystal
and analyzed those emission spectra (vide infra). Detailed analysis of those spectra
has revealed that there is a close relationship between the peak location of emission
lines and emission direction. Thus, to analyze the angle-dependent emission spectra
turns out to be a powerful tool to accurately determine the dispersion of propagation
constant of the laser material.
In a light-emitting device, we must consider a problem of out-coupling of light.
Seeking efficient out-coupling of light is equivalent to solving equations of electromagnetic wave motion inside and outside the slab crystal under appropriate boundary conditions. The boundary conditions are given such that tangential components
of electromagnetic fields are continuous across the interface formed by the slab
crystal and air or a device substrate. Moreover, if a diffraction grating is present in an
optical device (including the laser), the diffraction grating influences emission
(a)
P6T
(b)
2 µm
P6T crystal
AZO grating
optical device
(c)
air
Fig. 9.10 Construction of an organic light-emitting device. (a) Structural formula of P6T. (b)
Diffraction grating of an organic device. The purple arrow indicates the direction of grating
wavevector K. Reproduced from Yamao T, Higashihara S, Yamashita S, Sano H, Inada Y,
Yamashita K, Ura S, Hotta S (2018) Design principle of high-performance organic single-crystal
light-emitting devices. J Appl Phys 123(23): 235501/13 pages [7], with the permission of AIP
Publishing. https://doi.org/10.1063/1.5030486. (c) Cross-section of P6T crystal/AZO substrate
9.5 Lasers
363
organic light-emitting devices Yamao et al. [7] have developed a light-emitting
device where an organic crystal of P6T (see structural formula of Fig. 9.10a) was
placed onto a diffraction grating (Fig. 9.10b [7]). The compound P6T is known as
one of a family of thiophene/phenylene co-oligomers (TPCOs) together with BP1T,
AC5, AC’7, etc. that appear in Fig. 9.8 [10, 11]. The diffraction grating was
engraved using a focused ion beam (FIB) apparatus on an aluminum-doped zinc
oxide (AZO) substrate. The resulting substrate was then laminated with the thin
crystal of P6T (Fig. 9.10c). Using those devices, Yamao et al. excited the P6T crystal
with ultraviolet light of a mercury lamp and collected the emissions from the crystal
and analyzed those emission spectra (vide infra). Detailed analysis of those spectra
has revealed that there is a close relationship between the peak location of emission
lines and emission direction. Thus, to analyze the angle-dependent emission spectra
turns out to be a powerful tool to accurately determine the dispersion of propagation
constant of the laser material.
In a light-emitting device, we must consider a problem of out-coupling of light.
Seeking efficient out-coupling of light is equivalent to solving equations of electromagnetic wave motion inside and outside the slab crystal under appropriate boundary conditions. The boundary conditions are given such that tangential components
of electromagnetic fields are continuous across the interface formed by the slab
crystal and air or a device substrate. Moreover, if a diffraction grating is present in an
optical device (including the laser), the diffraction grating influences emission
(a)
P6T
(b)
2 µm
P6T crystal
AZO grating
optical device
(c)
air
Fig. 9.10 Construction of an organic light-emitting device. (a) Structural formula of P6T. (b)
Diffraction grating of an organic device. The purple arrow indicates the direction of grating
wavevector K. Reproduced from Yamao T, Higashihara S, Yamashita S, Sano H, Inada Y,
Yamashita K, Ura S, Hotta S (2018) Design principle of high-performance organic single-crystal
light-emitting devices. J Appl Phys 123(23): 235501/13 pages [7], with the permission of AIP
Publishing. https://doi.org/10.1063/1.5030486. (c) Cross-section of P6T crystal/AZO substrate
9.5 Lasers
363