Innovative synthesis, structural characteristics, linear and nonlinear optical properties, and optoelectric parameters of newly developed A2ZnGeO4 (A = K, Li) thin films

Abstract

The synthesis of high-quality thin films through spin coating deposition on meticulously cleaned glass substrates is presented. Optical band gaps E _g of both samples using the Kubelka-Munk function are determined. The data analysis uncovers the presence of optical allowed direct transition for A₂ZnGeO₄ (A = K, Li). Spectroscopic ellipsometry measurements on A₂ZnGeO₄ (A = K, Li) thin films and an analysis of their optical properties using the Cauchy model are presented. Furthermore, the increase of the thickness of the thin film results in improvements in their optoelectrical parameters, such as electrical conductivity, optical mobility, and optical conductivity. Using the Kubodera and Kobayashi comparative model, the third order nonlinear susceptibility (χ ⁽³⁾) was estimated based on the compounds' high linear absorption of the generated third harmonic wavelength (355 nm). This paper presents remarkable NLO results that reveal potential uses in optoelectronics and photonics.

Fig. 1. Schematic diagram of synthesis of A₂ZnGeO₄ (A = K, Li) compounds.

Fig. 2. XRD patterns of as-prepared (a) K₂ZnGeO₄ and (b) Li₂ZnGeO₄ compounds.

Fig. 3. SEM image of K₂ZnGeO₄ (a) and Li₂ZnGeO₄ (b), along with the elemental analysis by EDX of K₂ZnGeO₄ (c) and Li₂ZnGeO₄ (d).

Fig. 4. The TEM image of K₂ZnGeO₄ (a) and Li₂ZnGeO₄ (b) along with the particle size distribution of K₂ZnGeO₄ (c) and Li₂ZnGeO₄ (d).

Fig. 5. Raman spectra of the phosphors (a) K₂ZnGeO₄, (b) Li₂ZnGeO₄.

Fig. 6. The UV-vis absorbance spectrum A (λ) and dA/dλ as a function of λ in the inset for the phosphors K₂ZnGeO₄ (a) and Li₂ZnGeO₄ (b) at room temperature, spanning from 200 to 800 nm.

Fig. 7. Plots of (αhν)² as a function as hν of (a) K₂ZnGeO₄ and (b) Li₂ZnGeO₄.

Fig. 8. Variation of ln(αhν) against ln(hν − E_g) of (a) K₂ZnGeO₄ and (b) Li₂ZnGeO₄.

Fig. 9. Determining the Urbach energy of the (a) K₂ZnGeO₄ and (b) Li₂ZnGeO₄.

Fig. 10. Refractive index (a) and extinction coefficient (b) plots versus wavelength for K₂ZnGeO₄ and Li₂ZnGeO₄ compounds.

Fig. 11. The (n² − 1)⁻¹ as a function of (hν)² for K₂ZnGeO₄ (a) and Li₂ZnGeO₄ (b).

Fig. 12. The (n² − 1)⁻¹ as a function of λ⁻² for K₂ZnGeO₄ (a) and Li₂ZnGeO₄ (b).

Fig. 13. The ε₁ and ε₂ against the λ of the (a) K₂ZnGeO₄ and (b) Li₂ZnGeO₄.

Fig. 14. (a) The variation of ε₁ with λ₂ and (b) The ε₂ against λ³ for the A₂ZnGeO₄ (K, Li).

Fig. 15. (a) The variation of the optical conductivity and (b) the electrical conductivity versus the photon energy for the A₂ZnGeO₄ thin films.

Fig. 16. Third harmonic intensity plotted against the incident angle for polarization P and S of K₂ZnGeO₄ film and silica (a) and (b) and Li₂ZnGeO₄ film and silica (c) and (d).