Gallium oxide

For the solid state method: zinc oxide (99.99%, Strem Chemicals, Newburyport, MA, USA), gallium oxide (99.99%, Strem Chemicals, Newburyport, MA, USA), tin oxide (99.99%, Strem Chemicals, Newburyport, MA, USA), chromium oxide (99.99%, Alfa Aesar, Karlsruhe, Germany).
For the hydrothermal method: zinc nitrate hexahydrate (>99%, Alfa Aesar, Karlsruhe, Germany), gallium oxide (99.999%, Alfa Aesar, Karlsruhe, Germany), nitric acid (35 wt%), tin chloride pentahydrate (98%, Alfa Aesar, Karlsruhe, Germany), chromium (III) nitrate nonahydrate (99.9%, Alfa Aesar, Karlsruhe, Germany), ammonia solution (30 wt%), hydrochloric acid (50 mmol L⁻¹). All the chemicals were used as received without further purification.

Zinc nitrate hexahydrate (>99%) was purchased from Fluka. Gallium oxide (99.999%) and chromium (III) nitrate non-ahydrate (99.99%) were purchased from Alfa Aesar. (3-Aminopropyl)-triethoxysilane (99%) was obtained from Sigma-Aldrich. Dimethylformamide (>99.9%) was purchased from SDS. Alpha-methoxy-omega-N-hydroxysuccinimide poly(ethylene glycol) M_W 5.000 Dalton was bought from Iris Biotech GmbH. 1-Aminopropan-2-ol, methacryloyl chloride, tert-butanol (t-BuOH), dimethyl sulfoxide (DMSO), diethyl ether, ethyl acetate, acetone, methanol (MeOH), dimethylacetamide (DMA), dichloromethane (DCM), 2,2′azobis(isobutyronitrile) (AIBN), 4-cyano-4-(ethylthiocarbonothioylthio) pentanoic acid, 2-thiazoline-2-thiol, N-ethyl-N′-(3-dimethyl aminopropyl)carbodiimide hydrochloride were purchased from Merck-Sigma-Aldrich (Germany). Azo initiator V-70 was purchased from Wako Chemicals (Japan).