Revelation of luminescence-thermometry, light generation in first biological window and IR detection capabilities of sodium yttrium fluoride co-doped with Yb3+ and Er3+ ions synthesized by low-cost approach

Abstract

Microwave-assisted combustion synthesis approach is adopted to prepare sodium yttrium fluoride co-doped with ytterbium and erbium (NaYF4: Er3+/ Yb3+) nanoparticles. PXRD confirms the formation of mixed phase (cubic and hexagonal) of the NaYF4: Er3+/ Yb3+ crystal lattice. It is determined that the cubic phase dominates over the hexagonal phase. Three characteristic emission peaks appearing at 523, 544 and 672 nm are attributed to the transitions 2H11/2, 4S3/2 - 4I15/2 and 4F9/2 - 4I15/2 respectively which is character of Er3+ ions, confirming the potential in first biological window applications. The optimal dopant concentration is found and the asymmetric ratio is calculated. Strong up-conversion emission has been observed in the sample in the yellowish-green area when excited with 980 nm radiation. The life time of the 4S3/2 (green) and 4F9/2 (red) levels are found to be 1.187 and 0.472 ms respectively. The emission occurring in the synthesized sample follows the two-photon process which is confirmed by double log graph of intensity and pump-power. Thermal sensitivity is recorded in the range of 300–540 K. The thermally and non-thermally coupled levels attributed to the transitions (2H11/2 and 4S3/2) to (2H11/2 and 4F9/2) of Er3+ ions which are employed to study the temperature sensing. Higher relative sensitivities in both thermally and non-thermally coupled levels were observed in the samples with their values being 1.33 % K−1 and 1.81 % K−1 correspondingly. The significant thermal sensitivity of the synthesized phosphor materials improves its possibility in optical thermometric applications. Further to study the light-emitting abilities of the prepared phosphor, a phosphor-in-glass structure was fabricated using a borate-based glass system. The photometric parameters such as luminous efficacy of radiation and luminous efficiency were obtained to be 331 lm/Wopt and 48.46 % respectively. The prepared compound exhibits superior IR sensing which is evident upon exposure of the fabricated P-i-G to 980 nm radiation. The performed studies authenticate the capabilities of the cubic phase NYF in optical thermometry, light generation and IR detection abilities.