A number of calcium bismuthates were synthesized (25 to 50 mol% in Ca) and characterized by XRD, SEM, EDX, XPS and DRS techniques; the latter provided an estimate of the bandgap energies (E_bg=2.41 to 3.29 eV) via Tauc plots for indirect transitions, whereas XPS established the potentials (vs NHE) of their respective valence bands (and thus the conduction bands). Linear correlations existed between E_VB/E_CB and E_bg that when compared with those of strontium bismuthates (reported earlier) showed that differences in energies at E_bg=0 eV are related to the difference in the absolute electronegativities of Ca and Sr, from which the following empirical phenomenological rule is postulated: replacing one alkaline earth metal in bismuthates by another causes the points of intersection of the linear correlations E_CB(E_bg) and E_VB(E_bg) to be displaced by an amount equal to twice the difference in absolute electronegativities of these metals.

中文翻译：

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半导体光催化剂中电导/价带能和带隙能相关的现象学规则：铋酸钙与铋酸锶

合成了许多铋酸钙（Ca含量为25至50 mol％），并通过XRD，SEM，EDX，XPS和DRS技术进行了表征。后者通过Tauc曲线对间接跃迁提供了带隙能量（E _bg = 2.41至3.29 eV）的估计，而XPS确定了它们各自的价带（因而也就是导带）的电势（vs NHE）。E _VB / E _CB与E _bg之间存在线性相关，与铋酸锶锶的线性相关（较早报道）表明，E _bg处的能量差异= 0 eV与Ca和Sr的绝对电负性的差异有关，从中可以得出以下经验现象学规律：用另一种铋取代铋酸盐中的一种碱土金属会引起线性相关性E _CB（E _bg）和E _VB（E _bg）的位移量等于这些金属的绝对电负性差异的两倍。