The photoluminesce (PL) of Sn[2]P[2]S[6] crystals and their analogues
was studied in [1-3]. Sn[2]P[2]S[6] crystals have ferroelectric phase
transition (PT) at the temperature T[0ť ]336K and atmospheric
pressure. Phase diagrams p-T and p-T-x of Sn[2]P[2]S[6],
Sn[2]P[2]Se[6]and their ferroelectric solid solutions were
investigated in [4-6]. According to the position of maximum of the
fundamental PT the following values of the band gap E[g] were
determined [2]:
Pb[2]P[2]S[6]: E[g](300K) = 2.57; E[g](77K) = 2.79; E[g](4K) = 2.81 eV
Sn[2]P[2]S[6]: E[g](300K) = 2.33; E[g](77K) = 2.53; E[g](4K) = 2.55 eV
We have investigated the PL spectra of Sn[2]P[2]S[6], crystals at
various orientations of crystals and at different intensities of laser
beam energy. It was found that at room temperature there exists
classical fundamental PL, and also for the first time several intense
peaks of the impurity PL were found. The energies of the maxima
established have the following values:
Face "A" (eV)
2.1507
2.2119
2.2671
2.4478
Face "B" (eV)
2.1227
2.1805
2.2141
2.4340
It is seen that the obtained PL spectra of two "A" and "B" different
natural faces of the sample testify that the energy of the PL maxima
is different and this difference is due to the anisotropy of
Sn[2]P[2]S[6] crystal. The spectral dependences of the transmission
coefficient of crystal at different temperatures have been studied. It
was found that for the sample of 0,088cm thick and with the
transmission coeffient equal to 20% the fundamental absorption edge l
[ed] in ferrophase depends on the T temperature nonlinearly:
l [ed] [nm]= 481.2 + 307.5× 10³× T - 161× 10^-5× T2 + 430× 10^-8× T3.

[1]. Vysochanskii Yu.M., Slivka V.Yu., Perechinski S.I. et al./
Ukr.Fiz.Zhurn., v.25, N2, pp.281-284, (1980) (Ukraine).
[2]. Agekian V.F., Muzyka L.N. / FTT, v.28, N10, pp. 3217-3219,
(1986), (Russia).
[3]. Bravina S.L., Kadashchuk A.K., Manzhara V.S. et al./ Izv.
Acad.Nauk, seria fizicheskaya, v.57, N6, pp. 114-118, (1993),
(Russia).
[4]. Tyagur Yu.Il. and Jun J./ Ferroelectrics, 192, pp. 187-195,
(1997).
[5]. Tyagur Yu.Il. and Jun J./ High Pressure Science & Technology.
Procceedings of Joint XY AIRAPT &XXXIII EHPRC. International
Conference. Warsaw, Poland. pp.469-471, (1995).
[6]. Tyagur Yu.Il. and Jun J./ Ferroelectrics, 192, pp. 187-195,
(1998).

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