Nanooptics and photonics

Structural and photoluminescence properties of β-Ga2O3 nanocrystals obtained by mechanosynthesis
Luchechko A.1*, Vasyltsiv V.1, Kushlyk M.1, Slobodzhan D.1, Baláž M.2, Cebulski J.3, Szmuc K.4, Szlęzak J.3, Shpotyuk Y.1,3
1 Department of Sensor and Semiconductor Electronics, Ivan Franko National University of Lviv, Tarnavskogo Str., 107, Lviv 79017, Ukraine.
*E-mail: andriy.luchechko@lnu.edu.ua
2 Institute of Geotechnics of the Slovak Academy of Sciences
Watsonova str., 45, 04001, Košice, Slovakia
3 Institute of Physics, University of Rzeszow, Rzeszow, 35-959, Poland
4 Institute of Materials Engineering, University of Rzeszow, Rzeszow, 35-959, Poland.

The gallium oxide (β-Ga2O3) is a promising material for application in power electronics, solar cells, UV photodetectors, transparent electrodes, flat panel displays, and UV phosphors. Nanosized Ga2O3 has great potential application in optoelectronic nanodevices and gas sensors.
In this work, a series of β-Ga2O3 nanocrystals have been successfully obtained by the high-energy ball milling method, changing the milling conditions of the initial powder of gallium oxide. The obtained nanocrystalline powders have been characterized by multi-experimental methods including X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and luminescent spectroscopy. 
XRD patterns show mainly a single β-Ga2O3 phase (a monoclinic crystalline structure with a space group of C2/m) formed in the milling process with a small amount of -Ga2O3 phase. The grains of irregular shape were identified with the TEM technique. HRTEM images confirmed the formation of the β-Ga2O3 nanocrystals with a size distribution of 50-120 nm. 
Luminescence bands with maxima at about 380, 425 and 490 nm were observed in photoluminescence spectra. The blue shift of the emission maxima at the excitation in the fundamental absorption edge under the different milling conditions was detected. The excitation spectra are observed in the wavelength range from 230 to 400 nm and also depend on obtaining conditions of nanopowders.