Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)₂O₃, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900–2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)₂O₃ sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm₂O₃-Dy₂O₃, Sm₂O₃-Er₂O₃, and Dy₂O₃-Er₂O₃ systems.

Physical characteristics of Cu₂Te are poorly investigated due to limited Te sources available and unclear atomic positions of crystal structure. Herein, hexagonal Cu₂Te microdisks are successfully prepared via chemical vapor deposition procedure using GaTe as Te source. The epitaxial growth mechanism of the Cu₂Te hexagonal structures with the orthorhombic phase is rationalized by proposed layer‐over‐layer growth model. The photoluminescence (PL) spectrum of Cu₂Te microdisks shows a new red emission band in addition to usual infrared light emission due to Cu deficiency. Single Cu₂Te microdisk operates as an optical microcavity supporting whispering gallery modes for red lasing around 627.5 nm. This Cu₂Te microdisk microcavity exhibits a high quality factor of 1568 and a low lasing threshold of 125 kW cm⁻² at room temperature. Meanwhile, Cu₂Te microdisks have been exhibited as an ideal platform for surface enhanced Raman scattering (SERS) eliminating drawbacks of noble metal substrates with detection limitation to nanomolar level and an enhancement factor of ≈1.95 × 10⁵. Hexagonal Cu₂Te microdisks turn out to be an efficient microcavity for red lasing and low‐cost nonmetallic SERS substrates, opening potential applications in photonics and biological detection of aromatic molecules.