Effect of Yb concentration on the microstructures, spectra, and laser performance of Yb: CaF₂ transparent ceramics

Abstract

Ytterbium‐doped calcium fluoride transparent ceramics is considered as a promising laser gain medium. How to prepare low scattering loss ceramics is the main challenge at present. In this study, a simple route of hot‐pressing method was introduced to fabricate high optical quality of Yb: CaF2 laser ceramics with different concentration of Yb ions. The influence of Yb concentration on the particle sizes of the powders, microstructure, fluorescence spectra, output power, and laser emitting spectra of Yb: CaF2 transparent ceramics was discussed. About 976 nm LD pumped CW laser operation has been demonstrated in 1, 2, 4, and 5 at.% Yb doped CaF2 ceramics. A maximum average output power of 0.809 W was obtained for the 5 at.% Yb: CaF2 ceramics with the slope efficiency was 26%.

Cold Sintering of Highly Transparent Calcium Fluoride Nanoceramic as a Universal Platform for High‐Power Lighting

“…Normally, the ceramics prepared by CSP contain a significant amount of residual pores and amorphous grain boundaries (GBs) after the reaction involved grain growth, which is highly detrimental to the transmittance of ceramics. [ 11 ] Therefore, the transparent ceramic in visible‐light spectra has never been realized by CSP except for the one with an extremely low melting point of LiF. [ 12 ] Generally, the transmittance (T) of polycrystalline ceramic is expressed by the following equation, [ 13 ] $$\[ \begin{array}{*{20}{c}}{T\; = \;\left( {1\; - \;{R_s}} \right)\;{\rm{exp}}\left( { - \gamma d} \right)}\end{array} \]$$where R s describes the reflection losses at the two sample surfaces, γ is the total absorption coefficient, and d is the sample thickness.…”

“…d) TEM image of the microstructure on the CaF 2 ‐HCl nanoceramic, and HRTEM images of a clean and coherent GB. e) In‐line transmittance spectra for CaF 2 ‐HCl, UD‐CaF 2 ‐HCl, Deox‐CaF 2 ‐HCl and HP‐CaF 2 (dot line), [ 11 ] respectively. f) Digital image of CaF 2 ‐HCl, UD‐CaF 2 ‐HCl, and Deox‐CaF 2 ‐HCl ceramics on a printed paper (left), and photographs showing the view with and without CaF 2 ‐HCl nanoceramic under sunlight (right).…”

“…The in‐line transmittance of as‐prepared CaF 2 nanoceramic (CaF 2 ‐HCl) is ≈50–80% in the wavelength range of 400–800 nm (Figure 1e,f), which is similar to the ceramic densified by conventional hot‐press sintering (HP‐CaF 2 ) at 800 °C. [ 11 ] By contrast, the undoped CaF 2 ‐derived ceramic (denoted as UD‐CaF 2 ‐HCl) shows a translucent appearance with in‐line transmittance less than 40% in visible light, while the deoxygenated CaF 2 ‐derived ceramic (denoted as Deox‐CaF 2 ‐HCl) has even lower transmittance of ≈20%. Transmission electron microscopy (TEM) observation reveals that the transparent ceramic has a pore‐less, extremely fine, and uniform microstructure (Figure 1d).…”

“…Therefore, we selected the Yb 3+ doped CaF 2 nanoparticles as the starting powder for densification. As shown in Figure 1a,b, the doped CaF 2 nanoparticles possess an average grain size of 25.61 nm, which is almost [11] half of undoped CaF 2 nanoparticles. Intriguingly, the EDS elemental mappings reveal that both doped and undoped CaF 2 nanoparticles show segregated oxygen elements on the surface (Figures S2-S4, Supporting Information Figure 1c), which can be easily removed by immersing in acid (Table S1, Figure S5, Supporting Information).…”

“…Normally, the ceramics prepared by CSP contain a significant amount of residual pores and amorphous grain boundaries (GBs) after the reaction involved grain growth, which is highly detrimental to the transmittance of ceramics. [11] Therefore, the transparent ceramic in visible-light spectra has never been realized by CSP except for the one with an extremely low melting point of LiF. [12] Generally, the transmittance (T) of polycrystalline ceramic is expressed by the following equation, [13] T R d s γ ( )…”