Enhanced second harmonic generation and photoluminescence in Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass

Abstract

Non-linear optical properties and photoluminescence exhibited by Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass are presented here. The glasses of composition 1.5Li2O–2B2O3–0.5Nb2O5–0.5Ta2O5:xPr6O11 (x = 0.0025, 0.005, and 0.01) were synthesized via the conventional melt-quenching technique, and the nanocrystal growth was induced by subjecting the as-quenched glasses to heat treatment between 530 and 560 °C for 3 h. Coalesced nanocrystals of sizes in the 20–38 nm range, resulting in the formation of dendritic spherulites, were obtained from the isothermal heat treatment. Effect of doping on the structural units of LiNb0.5Ta0.5O3 lattice was analysed by Raman studies, which indicated that Pr ions occupied Li+ vacancies or Nb/Ta antisites. A strong red emission at 620 nm, due to 1D2 → 3H4 electronic transition of Pr3+ ions, was observed upon excitation by a 450 nm radiation. The maximum intensity was exhibited by the composition corresponding to Pr-doping level, x = 0.005, while the crystallization had a pronounced effect on the intensity of the red output. A non-linear optical coefficient as high as 0.77 pm/V (twice that of d36 of potassium dihydrogen phosphate single crystal) was obtained from the bulk glass–nanocrystal composites of the composition in which x = 0.0025.