In the case of low (1 mol%) concentration of dopants the synthesis yields pure ZnO phase with no detectable impurities with the exception of metallic Sb where a small amount of Sb is observed in XRD and EDX. In the case of P-doping XRD patterns (Fig. ) reveal the presence of Zn 3 (PO 4 ) 2 , which proves that reaction (1) indeed takes place in the high-pressure cell. Doping with Zn 3 Sb 2 interestingly leads to formation of ZnSb phase [ICDD 5-714] that can be observed in XRD patterns (Fig. ). The change in atomic ratio between Zn and Sb compared to Zn 3 Sb 2 implies that zinc partially incorporates in the ZnO structure. Effects of Zn-doping can be particularly seen in photoluminescence of such samples as discussed later. Additionally, powder XRD patterns may contain lines from dopant-unrelated impurities -primarily carbon and silicates from the material of the high-pressure cell. However, these impurities can be removed mechanically during crystal selection. Overall, information about the samples with the respective names, composition and results of powder XRD and morphology analysis is summarized in Table . The best results in regard of single crystal size were achieved by doping with elemental Sb and As reaching 200 μm in diameter. These crystals were also used to study dopant concentrations by EDX measurements. The average concentration in at least 10 crystals was found to be ~0.3 at% for both As and Sb.