Growth of the (Ga69.5La29.5Er)2S300 Single Crystal and Mechanism of Stokes Emission.

The investigation of the properties of novel multicomponent chalcogenide single crystals is one of the principal directions of modern semiconductor optoelectronics. Particular attention is paid to the study of the photoluminescence properties of rare earth-doped chalcogenide semiconductors in the visible and near infrared range. This is due to the use of these materials in telecommunication devices, laser and sensor technology. We describe here the growth technique of the single crystal (Ga_69.5La_29.5Er)2S₃₀₀ composition by solution-melt method. X-ray diffraction methods confirm its crystallization in the space group Pna21. Optical absorption spectrum of the single crystal in the visible and near infrared range was studied. Using the functional dependence of (αhv)² on hv for direct transitions, the bandgap energy of the semiconductor was determined as 1.99 ± 0.01 eV. The increase in the dopant concentration from 0.2 to 0.4 at. % Er does not significantly change the band structure of the single crystal, therefore the bandgap energy is unchanged as well. Narrow absorption bands were recorded that are related to the transitions ⁴I_15/2 → ⁴I_11/2, ⁴I_15/2 → 4I9/2, ⁴I_15/2 → ⁴F_9/2 in the f-shell of erbium ions. High concentration of energy levels in the band gap associated with the structure defects of the crystal results in the high value of the optical absorption coefficient. Photoluminescence excitation was achieved by a 532 nm (2.33 eV) laser at 150 mW. Intense Stokes photoluminescence bands were recorded at 1.53 and 0.805 eV, as well as lower-intensity maxima at 1.45, 1.27, 1.88 eV. These emission bands correspond to the transitions 4I9/2→⁴I_15/2, ⁴I_13/2→⁴I_15/2, 4S3/2→⁴I_13/2, ⁴I_11/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 in Er³⁺ ions, respectively. An energy transition diagram for the f-shell of Er³⁺ ions in the (Ga_69.5La_29.5Er)2S300 single crystal was plotted. The emission mechanism and the important role of the cross-relaxation processes between the ground and excited states of Er³⁺ ions were established. As a result of the influence of the local crystalline field on erbium ions, the Stark splitting of the ⁴I_13/2, ⁴I_15/2 levels and the widening of the photoluminescence band with the maximum at 0.805 eV is observed. Intense infrared bands of the photoluminescence (1.53 and 0.805 eV) create prerequisites for using the (Ga_69.5La_29.5Er)2S300 single crystal in sensor technology and optoelectronic devices. [ABSTRACT FROM AUTHOR]