Enhanced Optical Nonlinearity in Bi³⁺-Doped CePO₄ Nanostructures for Optical Limiting Applications

Abstract

Pure and Bi 3+ -doped CePO 4 were synthesized by the simple co-precipitation method. Successful dopant incorporation into the host lattice of orthophosphate without altering the crystalline structure was confirmed by structure analysis, X-ray diffraction, and Raman characterization. Morphological investigation was done using HR-SEM which portrays the co-existence of nanospheres and nanorods in doped CePO 4 and only nanospheres in pure CePO 4 . X-ray photoelectron spectroscopy studies confirm the +3 oxidation state of Ce 3+ and Bi 3+ with the presence of a trace amount of Ce 4+ in the as-prepared nanoparticles. Vibration sample magnetometer studies show weak ferromagnetic behavior of the nanostructures at room temperature. The absorption band in the wavelength range 200−300 nm accounts for 4f−5d electronic transition, and a red shift in the band edge is due to the increase in the band gap with the addition of the dopant. Photoluminescence emission spectra show broad blue-green emission owing to transition of Ce 3+ from the excited state to the ground state and also due to oxygen vacancy. The nonlinear optical absorption and optical limiting (OL) behaviors of Bi 3+ -doped cerium orthophosphate (CePO 4 ) were investigated using an open-aperture (OA) Z-scan technique under an excitation source of 532 nm nanopulsed lasers. The recorded OA transmittance curve reveals a transition from saturable absorption to reverse saturable absorption in pure CePO 4 at 2.46 GW/m 2 , whereas all the doped samples exhibit RSA attributed to 2PA. The increase in the nonlinear absorption (NLA) coefficient with on-axis intensity and the availability of the near resonant energy state due to the Bi 3+ dopant ensure the sequential 2PA (1PA + ESA) phenomenon. Compared to pure CePO 4 , doped nanostructures show improved NLA coefficients due to the availability of the defect state and oxygen vacancies in Bi 3+ -doped CePO 4 . Interestingly, a lower OL threshold (OLT) of 0.14 × 10 −13 W/m 2 is observed in 0.3% Bi 3+ -doped CePO 4 . The lower OLT value of Bi 3+ -doped CePO 4 ensures its potential candidature for OL applications in protecting optical sensors and human eyes.

Comment on “Charge Transfer-Triggered Bi3+ Near-Infrared Emission in Y2Ti2O7 for Dual-Mode Temperature Sensing”

“…The emission of Bi 3+ has been reported in many oxide systems, including oxides, , aluminates, ,, zirconates, germanates, , silicates, scandates, vanadates, titanates, and phosphates, , and it is a coactor in many of these systems. Historically, Bi 3+ has been known as a near UV-emitter, from 3 P 1 , 3 P 0 states to the 1 S 0 ground state, usually in the region of 300–400 nm, although the host lattice can modify the emission wavelength .…”