To fulfil the requirements of operating at low temperature in a harsh environment, the investigation on optical thermometers plays an increasingly important role. In this work, the influence of vanadium concentration on the capability of temperature readout by La₂MgTiO₆:V⁵⁺,Cr³⁺ luminescent thermometers was investigated for the first time. The presence of V³⁺ and V⁵⁺ was verified by XPS and absorption measurements. In the emission spectra, a blue–green emission region was assigned to both host and V⁵⁺ emission. Moreover, a spin-forbidden emission of Cr³⁺ ions was also detected. Vanadium ions in the +3 oxidation state do not exhibit luminescence, but play a role as a charge compensator. The highest emission intensity was obtained from the sample doped with 0.1% V. Besides, with increasing vanadium concentration, a redshift in the maximum position of the spectrum was observed corresponding to a movement from the greenish blue to yellowish green region in the CIE1931. It was shown that the relative sensitivity (S_r) and the temperature operating range can be easily modified by changing the concentration of vanadium ions. In particular, the outstanding relative sensitivities of 1.71% K⁻¹ (at 187 K) and 1.96% K⁻¹ (at 165 K) obtained from La₂MgTiO₆:0.1%V⁵⁺,Cr³⁺ and La₂MgTiO₆:0.05%V⁵⁺,Cr³⁺ demonstrated the enormous potential of this material for thermal sensing application.

Here we present new findings of a comprehensive study of the fundamental physicochemical properties for GeS and GeSe in bulk form. UV and X-ray photoelectron spectroscopies (UPS/XPS) were employed for the experiments, which were carried out on in situ cleaned (100) surfaces free from contamination. This allowed to obtain reliable results, also unchanged by effects related to charging of the samples. The work functions, electron affinities and ionization energies as well as core level lines were found. The band gaps of the investigated materials were determined by photoreflectance and optical absorption methods. As a result, band energy diagrams relative to the vacuum level for GeS and GeSe were constructed. The diagrams provide information about the valence and conduction band offsets, crucial for the design of various electronic devices and semiconducting heterostructures.