Thermal, Optical, and IR-Emission Properties of Extremely Low Hydroxyl TeO₂-WO₃-Bi₂O₃-La₂O₃-xEr₂O₃ Glasses for Mid-Infrared Photonics

Round 1

Reviewer 1 Report

I read this work with great interest.

I was impressed with the quality of the results and glass samples obtained. The research group from Russia is constantly publishing good results using ultra-pure telluride glass, which is a challenge itself.

I recommend the publication as submitted.

Author Response

The authors say "thank you" to the Reviewer#1 for the kind words.

Reviewer 2 Report

The authors have presented their work using TeO2-WO3-Bi2O3-La2O3-Er2O3 glass and characterizing their luminescence intensities and lifetimes near the wavelengths of 1.53 and 2.75 um. I feel that the authors have done a comprehensive study and I am of the opinion that this work can be published in its present stage. However, I have a few optional comments which the authors can decide if they wish to add them to their manuscript.

1) Why are the tablets 0.2 cm thick used for the majority of optical measurements while the longer samples (0.6-1.5 cm long) applied for OH volume absorption evaluation for erbium containing compositions? Can the authors clarify their decision?

2) In the characterization of the samples (figure 3), are the measurement setup purge of H2O presence? How do the authors avoid the impact of absorption for the water vapor in the atmosphere?

3) For Figure 6, I would suggest that the authors place the fitted line equation on the graph since the gradient is relatively small.

Author Response

The authors have presented their work using TeO2-WO3-Bi2O3-La2O3-Er2O3 glass and characterizing their luminescence intensities and lifetimes near the wavelengths of 1.53 and 2.75 um. I feel that the authors have done a comprehensive study and I am of the opinion that this work can be published in its present stage. However, I have a few optional comments which the authors can decide if they wish to add them to their manuscript.

1) Why are the tablets 0.2 cm thick used for the majority of optical measurements while the longer samples (0.6-1.5 cm long) applied for OH volume absorption evaluation for erbium containing compositions? Can the authors clarify their decision?

The tablets 0.2 cm thick were used for the majority of optical measurements, since the specifics of measuring the refractive index and luminescent properties require thin samples. Spectroscopy allows the use of longer samples, and these measurements were carried out and presented in the manuscript.

2) In the characterization of the samples (figure 3), are the measurement setup purge of H2O presence? How do the authors avoid the impact of absorption for the water vapor in the atmosphere? 

The cuvette section was not subjected to special purge procedures of H₂O presence. The water vapor absorption comb in the air is in the range of 2.5-2.8 microns and does not interfere with the determination of the volume concentration of hydroxyl in the glasses using a band of 2.8-3.3 microns.

3) For Figure 6, I would suggest that the authors place the fitted line equation on the graph since the gradient is relatively small.

A good idea that will help illustrate the weakness of the dependence. The equations of the fitted lines were placed on the graph of Figure 6. The corresponding sentence was inserted into the text:

", the values of the slope of the lines are on the order of -0.001 (Figure 6)."

Reviewer 3 Report

The manuscript from Dorofeev et al. investigated the thermal, optical, and IR-emission properties of tellurite glass by comparing different amounts of Er2O3. The manuscript is well structured and is subject to reasonable systematic study, which can be published after minor revision.

1. the sentences on page 3 are confusing:

“… due to the moderate phonon energy of ~ 900 cm [2,5,24]. With continuous wave (CW) pumping at the 4I15/2-4I11/2 transition, this leads to a high population at the 4I13/2 level and a small population at the 4I13/2 level.”

“However, there are practically no studies of glasses of the tungsten-tellurite system, which have already proven their promise for fiber optics applications.”

2. line 172 on page 5, the author wrote “… expression ln(100/T%), taking into account Fresnel reflection.” However, there is no Fresnel reflection part included.
3. “formula α = (ln(100/T%) - 2β) / L (cm-1);” what is the prefactor 2 from? Is this from the two surfaces on the front and back. In this case, the formula disregards the side surface which requires normal incident and weak scattering media.
4. on page 8, 2β≈0.003, how do the authors estimate this value?

Since the latter concentration of hydroxyl estimation is based on that, therefore, the estimation of the value beta should be clarified.

5. support figure is missing for the statement “The measured lifetimes of the 4I13∕2 level of Er3+ ion are 7.0 and 6.5 ms for the Er2O3 content 0.4 and 4 mol%, respectively.”
6. on page 11, the last paragraph, the author stated the concentration quenching was mainly from hydroxyl, how this related to the “the absence of ion clustering”?

Author Response

The manuscript from Dorofeev et al. investigated the thermal, optical, and IR-emission properties of tellurite glass by comparing different amounts of Er₂O₃. The manuscript is well structured and is subject to reasonable systematic study, which can be published after minor revision.

1. the sentences on page 3 are confusing:

“… due to the moderate phonon energy of ~ 900 cm [2,5,24]. With continuous wave (CW) pumping at the 4I15/2-4I11/2 transition, this leads to a high population at the 4I13/2 level and a small population at the 4I13/2 level.”

“However, there are practically no studies of glasses of the tungsten-tellurite system, which have already proven their promise for fiber optics applications.”

The mistakes have been corrected:

"at the ⁴I_13/2 level" changed to "at the ⁴I_11/2 level"

“However, there are practically no studies of glasses of the tungsten-tellurite system, which have already proven their promise for fiber optics applications.” changed to "However, information about the properties of erbium-activated glasses of the lanthanum-tungsten-tellurite system is insufficient, although they have already proven their promise for fiber optics applications [5,7,32]."

2. line 172 on page 5, the author wrote “… expression ln(100/T%), taking into account Fresnel reflection.” However, there is no Fresnel reflection part included.

Indeed, the absorption calculation formula does not include Fresnel reflection part. Since we are considering only the hydroxyl band here, all the effects that reduce transmission, together with Fresnel reflection, were taken into account when subtracting with a straight line. This is clear from the figure 5, where the beginning and end of the hydroxyl band go to zero.

To clarify the processing, an explanation has been added.

"...expression ln(100/T%), taking into account Fresnel reflection." changed to "...expression ln(100/T%), taking into account Fresnel reflection by subtracting straight line."

3. “formula α = (ln(100/T%) - 2β) / L (cm^-1);” what is the prefactor 2 from? Is this from the two surfaces on the front and back. In this case, the formula disregards the side surface which requires normal incident and weak scattering media.

Really, β is the absorption on one surface, the prefactor 2 from two surfaces on the front and back. Taking into account the side surface is not required, we consider only the absorption of hydroxyl, which consists of volume part and ends' surfaces part.

The explanation was added: "...2β is the absorption by surface hydroxyl groups on the ends" instead of "...2β is the absorption by surface hydroxyl groups".

4. on page 8, 2β≈0.003, how do the authors estimate this value?

Since the latter concentration of hydroxyl estimation is based on that, therefore, the estimation of the value beta should be clarified.

It is our mistake - references to sources were missed. Since only the approximate value was needed in this work, we did not calculate the surface absorption of hydroxyl, but took averaged data from other papers.

We have inserted the necessary links:"(on the average 2β»0.003 for polished samples of tungsten-tellurite glasses of similar compositions)" converted to "(on the average 2β»0.003 for polished samples of tungsten-tellurite glasses [32,33])"

5. support figure is missing for the statement “The measured lifetimes of the 4I13∕2 level of Er3+ ion are 7.0 and 6.5 ms for the Er2O3 content 0.4 and 4 mol%, respectively.”

The necessary measurements were carried out, we have the dependency graph of the Intensity of 1,53 µm emission (see below). Often, publications show only the results of calculating lifetimes as tabular data. In this case, we have given a dependency graph for level ⁴I_11/2 as an example, and for level ⁴I_13/2 we consider it sufficient to present the values of lifetimes.

6. on page 11, the last paragraph, the author stated, how this related to the “the absence of ion clustering”?

We didn't mention the concentration quenching from hydroxyl groups on page 11, in the last paragraph.

However, the main channel of nonradiative relaxation in low-doped Er³⁺/tellurite glasses obtained by a trivial method in air is really quenching on vibrations of OH groups. But in our case the concentration of hydroxyl groups is inferior to the concentration of Er³⁺ by at least 10⁴ times, this allowed us to study the effect of only erbium ions on the emission characteristics.

To clarify which ions we had in mind, the following change is made:

“…can confirm the absence of ion clustering in glasses [25].” converted to “…can confirm the absence of Er³⁺ ions clustering in glasses [25].”