Rare-earth 1990; Zakery and Elliott 2007). The structural

Rare-earth (RE)-doped glass fiber amplifiers operating at a 1.3 ?m
wavelength band have received extensive attention due to the zero dispersion of
the silica fiber glass in the 1.3 ?m-wavelength region, and most installed
fibers worldwide are optimized at this wavelength.                 (Yang et al. 2005; Heo 2002;
Hewak et al. 1994 and Wei et al. 1994). In contrast, Dysprosium rare earth
atoms, Dy which have an active unfilled f shells in its electronic
configuration (Xe 4f104s2), can provide
1.3 ?m emission due to the 6F11/2, 6H9/2?6H15/2
transition (Tang et al. 2008). In addition, Dy has a good absorption band at
approximately 800 nm, at which level a cheap commercial laser diode could be
used for excitation. On the other hand, amorphous Selenium (a-Se) is
characterized by existence of localized states in its mobility gap. These
states are created due to presence of structural defects and absence of long
range order (Mott and Davis 1979; Elliott 1990; Zakery and Elliott 2007). The
structural disorder made a-Se and its alloys to have a high optical transparency
in the infra-red (IR) spectral regions up to 10 ?m. Besides, it has large
refractive index, thermal stability and high degree of covalent bonding.
Furthermore, due to high rare earth solubility, high emission quantum
efficiency (Park et al. 2008) and the low phonon energy (~ 250 cm-1)
of amorphous selenides compared with fluorides (~ 550 cm-1), or
oxide glasses (~ 1100 cm-1) (Heo 2008) it could be used as a suitable
host medium for Dy ions to enhance its mid-IR laser emission. It should be
noted that the low phonon energy of a-se decreases the multi phonon relaxation
which enables an active transition between rare earth atom levels in the middle
IR spectral region. Consequently, the exploration of the optical properties of
doped a-Se with Dy ions is very important to improve the performance of Laser
emission (Shen et al. 2015).ha1 

 ha1The latest achievements in
the development of chalcogenides doped rare earth ions (RE) studied in recent
years for active applications of photonic devices such as fiber
amplifiers,  biosensors, optoelectronic chips,
3D optical recording, luminescent labels, white light up-conversion emission,
color display and the near and mid-IR 1-5, The low phonon energy
(<500 cm-1) and high refractive indices of chalcogenides glasses hosts bring about high quantum efficiencies for rare earth ions transitions and larger oscillator strengths of RE dopants 6,7. The physics of rare earth ions is very interesting. However, in solid state laser materials such as doped crystals and glasses. The 4f electron shell determines the optical properties of rare earth ions; it is almost insensitive to the surrounding atom of the host environment because of transmission by 5s and 5p electron shells. This is the reason for weak interaction between optical centers and the crystalline field (weak electron–phonon coupling). Such weak interactions between the 4f electrons and the crystalline field produce a very well-resolved Stark structure of the levels, which varies slightly from host to host. For the same reason, electronic transitions in trivalent rare earth ions (RE3+) are very narrow and demonstrate very weak phonon bands. Among the rare earth ions, the Dy3+ ion is one of the best appropriate candidates for analyzing the energy-efficient luminescent materials 8, 9. In contrast, Dysprosium rare earth atoms, Dy which have an active unfilled f shells in its electronic configuration (Xe 4f104s2), can provide 1.3 ?m emission due to the 6F11/2, 6H9/2?6H15/2 transition 10. In addition, Dy has a good absorption band at approximately 800 nm, at which level a cheap commercial laser diode could be used for excitation. Conversely, the physical structure of amorphous selenium (a-Se). For a long time, the structure of amorphous selenium was assumed to contain a random mix of selenium chains (Sen) and 8-ring structures (Se8) distributed randomly throughout the solid.  The filled lone pair (LP) p of Selenium states forms the bonding (s) band while the empty anti-bonding p states form anti-bonding (s*) band. The valence band of Se is formed from the lone pair p electrons and the valence s states of Se lie far below the top of the valence band 11. During crystallization, the chains of Sen and Se8 rings transforms into hexagonal and monoclinic structure in sequence.  

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