Enhancement of the sensitivity of single band ratiometric luminescent nanothermometers based on Tb3+ ions through activation of the cross relaxation process

Abstract

the description of luminescent processes and their thermally induced changes, that may be also influenced by the optically active ions concentration, and thus by the various inter-ionic processes, is the key to the improved development of luminescence thermometry. A phosphor doped with only trivalent terbium ions was described, which, by using two excitation lines fitted to the 7 f 6 → 5 D 3 and 7 f 5 → 5 D 3 transitions, shows a luminescent signals with the opposite characteristics of intensity changes as a function of temperature. By modifying the concentration of tb 3+ ions, the probability of { 5 D 3 , 7 f 6 } ↔ { 5 D 4 , 7 f 0 } cross-relaxation was being altered, which turned out to have a beneficial effect on the properties of the described nanothermometers. the ratio of intensities for both excitations was found to be temperature dependent, which resulted in high relative sensitivities of temperature readout reaching 3.2%/°C for 190 °C and not reaching values below 2%/°C in the broad range of the temperature. extensive decay time measurements for 5 D 3 and 5 D 4 emissive levels were presented and the variability of both rise-and decay times as a function of terbium concentration and temperature was investigated. thanks to this, conclusions were drawn regarding thermally dependent optical processes occurring in a given and similar systems. The technique of high-resolution noncontact temperature measurement in the single-band-ratiometric (SBR) approach has been recently developed 1-6. It is an application of luminescence thermometry technique 7-10 which requires only one type of optically active center in any nanocrystalline matrix, and enables temperature readout with high resolution and significant relative sensitivity (S r). This approach has all the advantages of a ratiometric measurement 11-22 , and at the same time does not show susceptibility to partial signal interference by the possible changes in the transmission characteristics of the medium 23. The ratio of two spectrally separated bands is receptive to artificial alterations through various, not only thermal, factors modifying their shape, especially in biological media 24. The phosphors used in this approach may be based on different luminescent dyes or ions, whose emission intensity depends on the temperature in opposite ways, depending on the excitation line used. There can be many reasons for different temperature dependencies. The various conformational changes occurring in organic phosphors that result in a change in the shape of the absorption bands should be mentioned. In addition, it is possible to use an energy mismatch between energetic states, so that a given excitation line does not have a regular dependence of the resultant emission intensity on the temperature. Additionally, different types of energy transfers between optically active centers are possible, which may cause different dependence of emission intensity depending on the center which is excited using a given excitation wavelength. Nevertheless, one of the most promising...

Synthesis and luminescence spectroscopy study of a novel orange‐red colour emissions phosphor based on Tb3+ ion‐doped Na2ZnP2O7

“…The energy gap between the 5 D 4 level and the lower 7 F 0 level was high enough (~15 000 cm −1 ) to hinder its multiphonon relaxation, [ 47 ] then the W ph rate was also expected to be negligible. As 5 D 4 lifetime is experimentally constant, this eliminates concentration quenching (W q ) rate and, therefore, we could conclude that the experimentally observed lifetime should be close to the 5 D 4 radiative lifetime τ exp = τ rad .…”

Single‐Band Ratiometric Luminescent Thermometry Using Pr3+ Ions Emitting in Yellow and Red Spectral Ranges

“…KLaP 4 O 12 phosphors with different concentrations of Pr 3þ dopant substituting La 3þ ions, were synthesized using the coprecipitation method described by the authors earlier. [9,21,41] X-ray diffraction studies were carried out using a PANalytical X'Pert Pro diffractometer equipped with an Anton Paar TCU 1000 N temperature control unit using nickel-filtered Cu Kα radiation (V ¼ 40 kV, I ¼ 30 mA). TEM images were taken using Philips CM-20 SuperTwin TEM microscope.…”

“…This phenomenon was investigated both as a function of temperature, which activated the change of the particular energy states population, but also as a function of the dopant ion concentration and its influence on the thermally induced energy transfer in the Pr 3+ ‐doped systems. From the previous research of our group on Tb 3+ , [ 9,21 ] the highest dopant ion concentrations were expected to be optimal for Pr 3+ ions just like in the Tb 3+ ions case—however, it turned out that due to many possible CR processes, the optimal concentration for Pr 3+ ions is not so obvious. In previous modeling, [ 9,21 ] we have also shown that crystal matrices showing high‐energy phonons and a sufficient electron–phonon coupling should be beneficial for SBR thermometry.…”

“…Up to date, SBR thermometry based on the emission of several ions has been demonstrated, with most of the work focusing on lanthanides (Tb 3þ , Eu 3þ , or Nd 3þ) . [8][9][10][11][12][15][16][17][18][19]21] Due to the well-defined and complex energy-level scheme, this type of ions can be successfully used to carry out a temperature reading in the SBR approach, using an excitations matched to the ground-(GSA) and the excited-state absorption (ESA). Most of the up-to-date reported SBR luminescent thermometers concern the near infrared (NIR) (Nd 3þ ) [18,19] or greenemitting phosphors (Tb 3þ ), [9,10,12,17,21] while only a few reports present luminescent thermometers operating in the red and yellow spectral ranges.…”

“…[ 8–12,15–19,21 ] Due to the well‐defined and complex energy‐level scheme, this type of ions can be successfully used to carry out a temperature reading in the SBR approach, using an excitations matched to the ground‐ (GSA) and the excited‐state absorption (ESA). Most of the up‐to‐date reported SBR luminescent thermometers concern the near infrared (NIR) (Nd 3+ ) [ 18,19 ] or green‐emitting phosphors (Tb 3+ ), [ 9,10,12,17,21 ] while only a few reports present luminescent thermometers operating in the red and yellow spectral ranges. Up to date only Eu 3+ ‐doped phosphors have been evaluated as SBR luminescent thermometers operating in those spectral ranges.…”