# Spectroscopic Properties of Tb3+ Ions in TbF3-Doped CaF2 Crystals

## TL;DR

Tb3+-doped CaF2 crystals show strong green emission with high efficiency and stability, making them suitable for photonic applications.

## Contribution

The study reveals concentration-dependent spectroscopic properties and efficient cross-relaxation in Tb3+-doped CaF2 crystals.

## Key findings

- Tb3+-doped CaF2 crystals emit intense green light via the 5D4 → 7F5 transition.
- Quantum efficiency increases with Tb3+ concentration up to 10 mol%.
- Cross-relaxation processes enhance population of the emitting 5D4 level.

## Abstract

What are the main findings?
Tb3+-doped CaF2 crystals exhibit intense and stable green emission dominated by the 5D4 → 7F5 transition.Judd–Ofelt analysis provides radiative parameters of Tb3+-doped CaF2 crystal.The measured quantum efficiency increases from 31.4% (1 mol%) to 71.2% (5 mol%) and 73.9% (10 mol%).

Tb3+-doped CaF2 crystals exhibit intense and stable green emission dominated by the 5D4 → 7F5 transition.

Judd–Ofelt analysis provides radiative parameters of Tb3+-doped CaF2 crystal.

The measured quantum efficiency increases from 31.4% (1 mol%) to 71.2% (5 mol%) and 73.9% (10 mol%).

What are the implications of the main findings?
Efficient green emission is achieved at moderate–high Tb3+ concentrations without strong quenching.Cross-relaxation (5D3 → 5D4) enables effective population of the 5D4 emitting level.CaF2:Tb3+ combines millisecond lifetimes (~4.4–6.7 ms) with high QE, suitable for photonic applications.

Efficient green emission is achieved at moderate–high Tb3+ concentrations without strong quenching.

Cross-relaxation (5D3 → 5D4) enables effective population of the 5D4 emitting level.

CaF2:Tb3+ combines millisecond lifetimes (~4.4–6.7 ms) with high QE, suitable for photonic applications.

Tb3+-doped CaF2 single crystals are attractive materials for green photonic applications due to their low phonon energy, high optical transparency, and efficient Tb3+ emission. In this work, CaF2 single crystals doped with different TbF3 concentrations (1, 5, and 10 mol%) were grown and systematically investigated in order to clarify the concentration-dependent spectroscopic behavior of Tb3+ ions in a fluorite host. Optical absorption spectroscopy, Judd–Ofelt analysis, steady-state and time-resolved photoluminescence, colorimetric evaluation, and emission cross-section and gain calculations were employed. Judd–Ofelt intensity parameters typical of fluoride hosts were obtained, enabling the calculation of radiative transition probabilities and lifetimes. The emission spectra are dominated by intense green luminescence from the 5D4 → 7F5 transition, while the absence of 5D3 emission is attributed to efficient cross-relaxation processes. Fluorescence lifetimes in the millisecond range show slight changes with Tb3+ concentration. Quantum efficiency increases from low to intermediate concentrations and tends to saturate at higher doping levels. CIE 1931 chromaticity coordinates confirm stable green emission, while emission cross-sections and gain parameters reveal a highest value for orange emission of 10 mol% TbF3-doped CaF2 crystal. These results indicate that CaF2:Tb3+ single crystals are promising materials for photonic applications.