Description
The development of rare-earth-doped halide perovskites continues to be of interest for applications in biosensing, light-emitting diodes (LEDs), and solar cells as less toxic alternatives to their lead-based counterparts. Rare-earth (RE) dopants are of particular interest because of their well-defined electronic transitions, which are useful in photonic and optoelectronic applications.
This work investigates how RE doping (Er$^{3+}$, Ho$^{3+}$) alters the optical properties of two lead-free halide perovskite compounds, Cs$_2$AgInCl$_6$ (CAIC) and Cs$_4$MnBi$_2$Cl$_{12}$ (CMBC). The main objective is to identify and analyze the absorption and emission transitions associated with Er$^{3+}$ and Ho$^{3+}$ ions and to examine the effect of the host lattice on their spectroscopic behavior. Comparative studies with the well-known lead-based compound KPb$_2$Cl$_5$ are also included.
Er$^{3+}$- and Ho$^{3+}$-doped CAIC and CMBC materials were synthesized using a hydrothermal method. Optical characterization was performed using emission and excitation spectroscopy. The observed spectral features were analyzed by calculating transition energies and assigning them to known rare-earth electronic energy levels. The Er$^{3+}$-doped materials exhibited identifiable transitions in both emission and excitation spectra that were consistent with established energy levels. In particular, Er$^{3+}$-doped CMBC showed strong red emission lines from the $^4F_{9/2} \rightarrow {}^4I_{15/2}$ transition, while Ho$^{3+}$-doped samples exhibited pronounced red emission lines from the $^5F_5 \rightarrow {}^5I_8$ transition.
Optical emission studies were performed under ultraviolet excitation as well as blue laser excitation at 405~nm and 450~nm. These results demonstrate that Er$^{3+}$- and Ho$^{3+}$-doped lead-free perovskites synthesized via hydrothermal methods exhibit visible emission lines that are of potential interest for photonic and sensing applications.