The Saturation of the Response to an Electron Beam of Ce- and Tb-Doped GYAGG Phosphors for Indirect β-Voltaics

Reviewer comment

Author response

Table 1 and Figure 1

The authors showed the XRD pattern and concluded that each sample was a single-phase material. However, it does not pointed whether these crystals are indeed of the expected composition.

This matter is clarified in the revised manuscript. Now it is written as follows:

The pure  garnet phase of the samples was confirmed by the X-ray diffraction method (2D Phaser by Bruker with linearly polarized Cu radiation kα-doublet 1.5406 and 1.5444 Å), as expected.

Figure 3 and Figure 5

A long lifetime component can be seen after 20 ms region in the decay spectra of luminescence. Does this mean the existence of another excited level originating from Tb? Or is it simply a background signal?

As seen from the kinetics, the tail part has amplitudes less than 0.001 in comparison with the peak. Moreover, the tail part is almost parallel to the time axis. We consider this to be background level.

Figure 4

The Gd/Y shown as a legend seems to be different from the composition shown in Table1. Also, there is unreadable character after GYAGG:Tb-2 in the Figure Caption.

The figure capture is revised as follows:

Room temperature PL spectra at excitation in Tb³⁺ interconfiguration transition (λex=273 nm) of GYAGG:Tb-2 and GYAGG:Tb-3  samples. Inset includes the Gd/Y ratio, assuming a homogeneous distribution of the Tb ions between positions occupied by Gd and Y ions. Therefore, the Gd and Y indexes are each increased by 0.1.

Unreadable character is corrected.

L159-161

It has been pointed out that Gd/Y=1.5 has a 20% lower emission intensity than Gd/Y=1.2/1.8. Can this be obtained from Figure 4? The vertical axis in Figure 4 is arb. unit, and such discussion can not be done. The authors should normalize the intensities by any methods such as excitation photon intensity.

Also, the substance name written here is not shown in Table 1, as mentioned in the previous comment.

Figure 4 is revised.

Appropriate sentence is revised:

The PL intensity for sample GYAGG:Tb-2, Tb = 0.2 is approximately 20% lower than for sample GYAGG:Tb-3. Therefore, the ratio of components close to the latter composition was used in the concentration series.

L173-174

The authors pointed out that excitation by a high-intensity electron beam reduces the decay constant by 20%. The reviewer recognized that such conclusion is obtained from Figure 6(b). On the other hand, nothing is discussed about Figure 6(a). Is such a lifetime reduction also obtained at 380 nm ? If not, why? 

Also, it is not clear what range the authors refer to as "low excitation intensity". 

The scintillation kinetics caused by a transition from the 5D3 level are depicted in Figure 6(a). This scintillation is quenched by nonradiative transfer  to the ⁵D₄ level. The aim of demonstrating this kinetics was to draw the reader's attention to the fact that scintillation from the ⁵D4 level has a rising part, which is explained by ⁵D_3--⁵D4 nonradiative intracenter transfer.

The appropriate sentence is revised.

The scintillation, which is caused by ⁵D₃ → ⁷F_Jtransition, is strongly quenched by the nonradiative transfer from the ⁵D₃ to the ⁵D₄state. As a result, there is a rising part s in the kinetics of the scintillation in the spectral range  of  the ⁵D₄ → ⁷F_J transition with a constant of 150 μ.

The appropriate number is included.

Figure 6(b) shows the results by excitation with high intensity electron beam, but the statistics seem to be bad. Generally, the statistics should be better using higher intensity beam. The authors need to account for this point.

We agree with the Reviewer. In fact, there is a scintillator response after a single accelerator pulse.

Also, the substance name written here is not shown in Table 1, as mentioned in the previous comment.

Checked, this is the sample #3 from the Table.

L211

The authors point out that n_Tb and n_Ce are larger than n_ex. However, the reviewer can not understand how to obtain parameter n_ex.

Fixed. We add the notation n_ex as initial concentration of excitations and add the sentence “Therefore, we can neglect the saturation effects due to the exhausting of non-excited activators.” in the text.

Reviewer comment

Author response

The authors studied the Saturation of the Response to An Electron Beam of Ce and Tb Doped GYAGG Phosphors for Indirect β-voltaics. The study is well organized and contains sufficient details about the crystal growth, and scintillation properties and are suitable to be published in this journal.

We thank the Reviewer for reading the manuscript and providing a positive response.

Reviewer comment

Author response

LinLine 36-39. This sentence is not entirely accurate. Authors should clearly specify what they mean. Ionizing radiation in garnets produces only redistribution of electron-hole pairs between existing vacancies and dopants, but it does not create new vacancy/interstitials. New vacancies and interstitials ( radiation damage) are produced via elastic collisions (using, for example, neutrons or heavy ions):

Karipbayev, Z. T., Kumarbekov, K., Manika, I., et al (2022). Optical, structural, and mechanical properties of Gd3Ga5O12 single crystals irradiated with 84Kr+ ions. physica status solidi (b), 259(8), 2100415.

Mironova-Ulmane, N., Sildos, I., Vasil'chenko, E., Chikvaidze, et al (2018). Optical absorption and Raman studies of neutron-irradiated Gd3Ga5O12 single crystals. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 435, 306-312.

Pankratova, V., Skuratov, V. A., Buzanov, O. A., (2022). Radiation effects in Gd3(Al, Ga)5:O12: Ce3+ single crystals induced by swift heavy ions. Optical Materials: X, 16, 100217.

We agree with the Reviewer, new references [15-19] are included in the list of the literature.  Appropriate sentence is revised.

Their radiation resistance under a different kind of ionizing radiation was confirmed by the authors [15-18]. Tolerance to ionizing radiation occurs in garnets because the formed color centers have absorption bands primarily in the ultraviolet region and do not overlap the Ce3+ scintillation band of such materials, which is typically localized in the yellow-green region of the spectrum [19-21].

TaTable 1. What can be said about the initial defectiveness of the samples? After all, this should manifest itself in the kinetics of scintillations under an electron beam?

It is described that samples are translucent.

Ceramic samples were translucent,  had >99.6% of theoretical density, which corresponds the range of 5.84–5.89 g/cm3 depending on composition, and optical transmission of 35–40% at 550 nm.  

LinLine 172. What does "at low excitation intensity" mean? Is it possible to give the corresponding values in electrons/mm2?

Specified.