An effective synthesis protocol for differently-doped (Eu3+/Gd3+/Tb3+) luminescent La-hydroxycarbonates and their derivatives oxycarbonates and oxides

In this work, we report a systematic investigation on the structural, thermal, and photoluminescent properties of Eu3+-, Gd3+-, and Tb3+-doped lanthanum hydroxycarbonates and their thermally derived oxycarbonates and oxides. All systems were synthesized through a combined co-precipitation/hydrothermal route followed by controlled calcination at 500 °C or 800 °C to selectively obtain monoclinic oxycarbonates or hexagonal oxides, respectively. Structural analyses confirmed the formation of homogeneous single-phase solid solutions for all doped systems across the three structural families. Thermal characterizations allowed the identification of precise decomposition stages, supporting the design of reproducible and phase-selective calcination cycles. Photoluminescence (PL) spectroscopy revealed that the monoclinic oxycarbonate phase exhibits the highest emission intensities and the most spectrally resolved transitions across all dopants, outperforming both hydroxycarbonate and oxide systems under the same doping conditions. This behavior is attributed to the favorable symmetry and reduced non-radiative losses associated with the oxycarbonate host, as further supported by a geometric rationale based on atomic packing factor (APF) analysis. To our knowledge, this is the first study to provide a direct and comprehensive structure–property correlation across these three host phases, synthesized under strictly comparable conditions, and evaluated with respect to their dopant-specific optical behaviors for their possible use in solid-state lighting and other optical-related applications.