Optical Properties and Upconversion Luminescence of BaTiO3 Xerogel Structures Doped with Erbium and Ytterbium

Abstract

Erbium upconversion (UC) photoluminescence (PL) from sol-gel derived barium titanate (BaTiO3:Er) xerogel structures fabricated on silicon, glass or fused silica substrates has been studied. Under continuous-wave excitation at 980 nm and nanosecond pulsed excitation at 980 and 1540 nm, the fabricated structures demonstrate room temperature PL with several bands at 410, 523, 546, 658, 800 and 830 nm, corresponding to the 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2→ 4I15/2 and 4I9/2→ 4I15/2 transitions of Er3+ ions. The intensity of erbium UC PL increases when an additional macroporous layer of strontium titanate is used beneath the BaTiO3 xerogel layer. It is also enhanced in BaTiO3 xerogel films codoped with erbium and ytterbium (BaTiO3:(Er,Yb)). For the latter, a redistribution of the intensity of the PL bands is observed depending on the excitation conditions. A multilayer BaTiO3:(Er,Yb)/SiO2 microcavity structure was formed on a fused silica substrate with a cavity mode in the range of 650–680 nm corresponding to one of the UC PL bands of Er3+ ions. The obtained cavity structure annealed at 450 °C provides tuning of the cavity mode by 10 nm in the temperature range from 20 °C to 130 °C. Photonic application of BaTiO3 xerogel structures doped with lanthanides is discussed.

Synthesis of Highly Luminescent Silica-Coated Upconversion Nanoparticles from Lanthanide Oxides or Nitrates Using Co-Precipitation and Sol–Gel Methods

“…The lower efficiency of the UC process for the O, OD-AC formulation can be attributed to the type of host matrix phase (cubic α-NaYF 4 or hexagonal β-NaYF 4 ) [18,19,21], which will be discussed later. The peaks at 520, 540 and 657 nm correspond to 2 H 11/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 , 4 F 9/2 → 4 I 15/2 optical radiative transitions of Er 3+ ions, respectively, as previously reported for UCNPs composed of the same trivalent lanthanide ions [39,40] and in a study of Er 3+ and Yb 3+ UC photoluminescence on films [41]. It must be noted that an enhancement of the photoluminescence was observed when structures where co-doped with both ions, with a photoluminescence intensity more than one order-of-magnitude higher with respect to materials doped only with Er 3+ [41].…”

“…The peaks at 520, 540 and 657 nm correspond to 2 H11/2 → 4 I15/2, 4 S3/2 → 4 I15/2, 4 F9/2 → 4 I15/2 optical radiative transitions of Er 3+ ions, respectively, as previously reported for UCNPs composed of the same trivalent lanthanide ions [39,40] and in a study of Er 3+ and Yb 3+ UC photoluminescence on films [41]. It must be noted that an enhancement of the photoluminescence was observed when structures where co-doped with both ions, with a photoluminescence intensity more than one order-of-magnitude higher with respect to materials doped only with Er 3+ [41]. The crystalline nature of UCNPs was confirmed by the corresponding XRD pattern (Figure 3a,b), with similar diffractograms to those previously reported for UCNPs with the same sensitizer-activator system (Yb 3+ -Er 3+ ) [45].…”