# Experimental and theoretical insights into Ce3+-doped optical fiber luminescence mechanisms under X-rays

Ismail Zghari, Hicham El Hamzaoui, Adriana Morana, Youcef Ouerdane, Bruno Capoen, Sylvain Girard, Aziz Boukenter, Mohamed Bouazaoui

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## To cite this version:

Ismail Zghari, Hicham El Hamzaoui, Adriana Morana, Youcef Ouerdane, Bruno Capoen, et al. Ex-
perimental and theoretical insights into Ce3+-doped optical fiber luminescence mechanisms under X-
rays. Radiation Physics and Chemistry, 2026, 243, pp.113675. 10.1016/j.radphyschem.2026.113675.
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# Experimental and theoretical insights into Ce³⁺-doped optical fiber luminescence mechanisms under X-rays

Ismail Zghari<sup>a, *</sup> <sup>Δ</sup>, Hicham El Hamzaoui<sup>a</sup>, Adriana Morana<sup>b</sup>, Youcef Ouerdane<sup>b</sup>, Bruno Capoen<sup>a</sup>, Sylvain Girard<sup>b,c</sup>, Aziz Boukenter<sup>b</sup>, Mohamed Bouazaoui<sup>a</sup>

## ARTICLE INFO

### Keywords:

Fiber sensors

Ce³⁺-doped optical fiber

Radioluminescence

Thermoluminescence

Optically stimulated luminescence

## ABSTRACT

In this paper, we present a combined experimental and theoretical approach allowing the analysis of the joint processes of radioluminescence (RL), phosphorescence (PP), and fibered thermoluminescence (FTSL) during and after exposure of a Ce³⁺-doped optical fiber to X-rays. The experimental study shows that the integrated signal originating from the three processes is temperature independent for cumulated dose at least up to 300 Gy (SiO₂). A theoretical model was used to fit the emission signal data, explaining the physical processes at stake and allowing the extraction of the trapped carriers' populations. Furthermore, on the applicative side, replacing FTSL with optically stimulated luminescence (OSL) also leads to an integrated signal linearly dependent as a function of dose rate and without dependence on the temperature of irradiation. Those results open perspectives for temperature-independent real-time emission dosimetry through a highly flexible, reliable and sustainable fibered optical setup.

## 1. Introduction

Silica-based optical fibers have attracted considerable interest in recent decades in the field of dosimetry, whether in medical applications, in nuclear environment, or in the space domain (Moradi et al., 2018; Hu et al., 2024; Rovera et al., 2023; Zubair et al., 2023; Zghari et al., 2024; Hoehr et al., 2019; Söderström et al., 2021). This interest is driven by several advantages offered by certain optical fibers compared to alternative solutions such as those based on electronic detectors or crystals (Girard et al., 2018; Chen et al., 2017).

First, silica glasses possess important chemical, thermal, and mechanical properties, which facilitate their transformation into optical fibers, making them less invasive and suitably “invisible”, particularly for in vivo dosimetry (Chen et al., 2017). Through accurate measurements of the dose delivered by small ionizing radiation beams, fibers could allow for precise evaluation of the impact of radiation on biological tissues. Some specialty optical fibers can serve as active dosimeters, offering real-time dose or dose rate measurements helping to ensure the quality of medical treatments and to allow immediate response in case of incidents or anomalies at nuclear facilities

(Benabdesselam et al., 2021; Zghari et al., 2025a). They can also be employed as passive dosimeters, enabling the measurement of the dose received by individuals exposed to ionizing radiation in the context of their professional activities (Benabdesselam et al., 2023). In addition, silica-based optical fibers have the advantage of being resistant to high doses of ionizing radiation (Cieslikiewicz-Bouet et al., 2021), with limited levels of radiation induced attenuation (RIA). Their cylindrical symmetry makes their response virtually independent of the angle of incident radiation beams. Optical fibers are also flexible and lightweight, enabling remote monitoring, making them ideal for applications where space is limited and microelectronics cannot be deployed. Furthermore, silica-based optical fibers, while radiation-resistant, are considered to be close to tissue-equivalence, thereby reducing the discrepancy between the measured dose and the actual dose received by the human body.

Numerous studies have highlighted the modification of optical fiber properties due to radiation exposure. Ionizing irradiation can affect the guiding, transmission, and emission properties of silica-based optical fibers (Gherardi et al., 1993; Girard et al., 2013). There are three main macroscopic processes resulting from radiation exposure:

<footnote><sup>a</sup> Univ. Lille, CNRS, UMR 8523-PhLAM-Physique des Lasers Atomes et Molécules, F-59000, Lille, France</footnote>

<footnote><sup>b</sup> Université Jean Monnet Saint-Etienne, CNRS, Institut D'Optique Graduate School, Laboratoire Hubert Curien UMR 5516, F-42023, SAINT-ETIENNE, France</footnote>

<footnote><sup>c</sup> Institut Universitaire de France (IUF), Ministère de L'Enseignement Supérieur et de La Recherche, 1 Rue Descartes, F-75005, Paris, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: ismail.zghari@univ-lille.fr (I. Zghari).</footnote>
Radiation-Induced Emission (RIE), Radiation-Induced Refractive Index Change (RIRIC), and Radiation-Induced Attenuation (RIA) (Marrone, 1981; Fernandez et al., 2003; Petrie et al., 2025).

In this study, we focus only on the first mechanism: RIE, which may involve various mechanisms from the fiber material and several main contributions can be distinguished. Firstly, Cerenkov emission has sometimes to be considered: this process occurs when a charged particle moves through a material at a speed greater than the phase velocity of light in that medium (Archambault et al., 2006). Besides, when a luminescent material is exposed to ionizing radiation, electron-hole pairs are generated and may either recombine almost instantaneously at luminescence centers, leading to the emission of radioluminescence (RL) (Oresegun et al., 2021), or become trapped in defects sites within the host matrix. Moreover, depending on the energy depth of charge traps inside the host matrix, the trapped charges can be released after irradiation under measurement conditions (ambient temperature and light), giving rise to a phosphorescence (PP) signal. This latter is also known as afterglow in the scintillator field. Finally, deeper traps, on the other hand, require external stimulation to release the charges. Hence, controlled thermal stimulation results in thermoluminescence (TL), also called ThermoStimulated Luminescence (TSL) (Refaei et al., 2014), while optical stimulation gives rise to Optically Stimulated Luminescence (OSL) (Okada et al., 2016).

Several studies have been dedicated to the RIE response of silica glasses doped with various optically active ions such as Ce³⁺, Cu⁺, Gd³⁺, Tb³⁺, etc., under X-rays (Benabdesselam et al., 2021; Zghari et al., 2025b; El Hamzaoui et al., 2019; Capoen et al., 2016). Furthermore, other research has focused on the RL response of these materials under proton beams, as well as electron beams (Girard et al., 2016; Veronese et al., 2010; Söderström et al., 2022). These studies have helped broaden our understanding of the RL response of silica-based active dosimeters under various types of irradiation. However, it is important to highlight that most of these studies have been conducted at room temperature. Yet, in many applications—such as in vivo dosimetry, space environments, or particle accelerator facilities—temperature can vary significantly. In this context, it becomes essential to thoroughly investigate the effect of temperature on the response of dosimeters in order to ensure their accuracy and reliability under diverse operating conditions. In the study (Zghari et al., 2023a), the radioluminescence (RL) response of cerium-doped glassy rods was examined over a wide range of irradiation temperatures. It was observed that the RL signal intensity increases with temperature. The associated simulations attributed this increase to enhanced detrapping of charge carriers—initially trapped in deep states within the bandgap—facilitated by thermal agitation. To overcome this thermal sensitivity, an innovative approach has recently been developed using gadolinium-doped glassy rods (Zghari et al., 2025b). This method relies in measuring the three luminescence processes: radioluminescence, phosphorescence, and thermoluminescence. Thanks to this integrated approach, it was demonstrated that the resulting dosimetric response is independent of irradiation temperature.

In this work, we adopt the same experimental approach to analyze the joint processes of RL, PP and TL in a Ce-doped optical fiber under X-rays. The use of optical fibers instead of glassy rods is likely to minaturize and better integrate dosimeters connected to transport fibers. Under ionizing irradiations, fiber silica core, doped with Ce³⁺ ions, provides strong light emission, the spectrum of which is broad and peaks in the blue, around 460 nm. In addition, Ce-doped matrices are known to be radiation-hardened. And finally, the luminescence of Ce³⁺ ions is reputed to be very fast (in the order of a few tens of nanoseconds) in comparison with other rare-earths.

The TL signal from the sample, collected through a transport fiber, is called Fibered Thermo-Stimulated Luminescence (FTSL). Remotely detecting the three signals (RL, PP and FTSL) via an optical fiber allows a precise control of the delay between TL measurement and the end of irradiation. The used setup provides in a versatile way of measuring the successive optical signals corresponding to the three different

mechanisms (RL, PP and FTSL), which enables an accurate comparison with the theoretical model. This latter model is based on the standard kinetic equations describing the evolution of carriers' populations in the different bands representing the doped core material. To this purpose, the kinetics of the RL, PP and FTSL signals are simulated at different temperatures using 50 trap levels and one recombination center (RC). As reported in (Benabdesselam et al., 2021; Zghari et al., 2023a), the RL and TL spectra show a broad emission band centered around 460 nm attributed to the allowed transitions 5d → 4f of Ce³⁺ ions. Hence, for both TL and RL processes, the Ce³⁺ ion constitute the R at the origin of this emission.

Finally, further experiments are carried out by varying the irradiation temperature or by using OSL instead of TL for the achievement of real-time and temperature-independent dosimetry.

## 2. Materials and experimental methods

### 2.1. Studied samples

The Ce³⁺-doped core part of the studied fiber was prepared using the sol-gel process at FiberTech Lille platform of the University of Lille, as described in a previous paper (El Hamzaoui et al., 2016). The obtained silica doped rod with 0.07 wt% of Ce and having an initial 8 mm diameter was first drawn at 2000°C into a cane of about 1.5 mm diameter. This cane was then jacketed with a pure silica tube (F300 from Heraeus) and drawn into a final fiber. Hence, the fiber core consists of a sol-gel doped central part (~50 µm in diameter) surrounded by a pure silica glass having an outer diameter ~125 µm, well adapted to the used radhard transport fibers. Samples of 1 cm length were cut in the obtained sol-gel-derived fiber and fusion-spliced to the transport fibers in the scope of RL/FTSL/OSL measurements.

### 2.2. Characterization

The experimental setup used for RL and for the FTSL measurements, as well as for the RL/OSL measurements, is shown in Fig. 1. It consisted in a 1 cm-long piece of the Ce³⁺-doped fiber, spliced on both sides to a 5 m-long, 125 µm-diameter radiation-hard multi-mode optical fiber (supplied by Exail). The external X-ray beam came from the LABHX facility of the Laboratoire Hubert Curien, operated at 100 kV and generating photons with an average mean energy fluence of ~40 keV. The X-ray dose rate was controlled by tuning the tube current. The doped fiber was exposed to the X-rays in a calibrated position of the irradiator. The emission signal from the doped section was then guided through the transport fiber to a photomultiplier module (PMT, H9305-13 Hamamatsu), having a spectral response covering the 180–900 nm range according to the manufacturer. This PMT shows the highest and flat sensitivity in the range 400–600 nm, which is completely in line with the wide emission band of Ce³⁺ ions in our samples as reported in previous studies (Benabdesselam et al., 2021; Zghari et al., 2023a).

To adjust the temperature, the sample was put on a temperature-controlled plate and measurements were performed over an irradiation temperature ($T_{irr}$) ranging from 153 K to 353 K. For each $T_{irr}$, the sample was exposed to five different dose rates ranging from 50 to 1000 mGy/s for 300 s at a specific dose rate (RL), and then, data acquisition was continued for 180 s without X-ray irradiation, enabling detection of the PP signal. The FTSL was then recorded from the initial temperature $T_{irr}$ up to the maximal one (353 K) with a heating rate of 5 K/min. It is worth noting that, during the RL measurement, the obtained signal was not affected by the Cerenkov effect, as in our case, the used irradiation source delivered photons of too low energies to initiate this emission. It was nor polluted by other parasitic signals coming from to the transport fiber, as this one was shielded by a thick lead hood.

On the other side of the sample, the second optical fiber was eventually used to bring the stimulation light to the sample for RL/OSL measurements that consists in detecting the optical signal under
<figure><img src="image_4.png" /><figcaption>Fig. 1. Illustration of the experimental setup used to characterize the optical response of the Ce³⁺-doped fiber exposed to X-ray beam.</figcaption></figure>

simultaneous X-ray irradiation and optical stimulation for 5 min. For this purpose, we used a supercontinuum white light fiber laser (SC-400-2 FIANIUM supercontinuum from NKT Photonics), delivering up to 2 W of power throughout the 400–2400 nm region. After passing through a 600 nm high-pass filter to avoid the spectral recovering with the Ce³⁺ emission centered around 450 nm, about 280 mW of this laser source reached the Ce-doped sample. The signal was collected by the PMT at different temperatures after passing through a 450 nm (FWHM = 40 nm) band-pass filter.

## 2.3. Model

The mathematical model used to simulate our experimental data is the one previously presented in (Zghari et al., 2023a, 2025b). It describes the fundamental processes, such as the generation of electron-hole pairs, the trapping and detrapping of charge carriers, as well as electron-hole recombination, as schematically illustrated in Fig. 2. These processes are modeled by a set of coupled nonlinear differential equations, which govern the evolution of the populations of trapped and free electrons and holes in the material. These equations take into account the dynamics of the charge carriers under irradiation, integrating the effects of irradiation and temperature. The set of coupled nonlinear differential equations is as follows:

$$ \frac{dn_c}{dt} = X - \sum_{i=1}^{k} n_c(N_i - n_i)A_{ei} + \sum_{i=1}^{k} n_i s_i \exp\left(\frac{-E_i}{k_B T}\right) - n_c A_r m \quad (1) $$

$$ \frac{dn_i}{dt} = n_c(N_i - n_i)A_{ei} - n_i s_i \exp\left(\frac{-E_i}{k_B T}\right) \quad (i = 1, \dots, k) \quad (2) $$

$$ \frac{dm_v}{dt} = X - m_v(M - m)A_h \quad (3) $$

<figure><img src="image_5.png" /><figcaption>Fig. 2. Schematic representation of the levels and processes involved in the optical response (RL, PP and FTSL) modelling with k electron traps and one RC. The different processes are: (1) electron-hole pairs production. (2) hole capture by RC, (3) electrons trapping, (4) electrons detrapping by thermal activation and (5) electron-hole recombination on RC with radiative emission.</figcaption></figure>

$$ \frac{dm}{dt} = m_v(M - m)A_h - n_c A_r m \quad (4) $$

$$ I = n_c A_r m \quad (5) $$

These equations express the time variation of: (1) the electron concentration in the conduction band (CB), (2) the electron concentration in the i-th trap, (3) the hole concentration in the valence band (VB), (4) the hole concentration in the RC and (5) the emission intensity.

The set of differential equations (1)–(5) was solved numerically using the Matlab software. It should be noted that the number of unknowns is greater than the number of equations, which complicates the direct solution of this equations system. To overcome this difficulty, a least squares method was implemented. This method allowed for the optimization of the transition coefficients ($A_{ei}$, $A_r$, and $A_h$), as well as the concentrations of the traps $N_i$, thereby reducing the number of unknowns and making it possible to obtain a system consistent with the number of available equations. The description of equations parameters is indicated in Table 1.

The determination of the parameter values, as well as the different steps of the simulation, are detailed and discussed in (Zghari et al., 2023b), where the complete procedure and justifications for the methodology are provided.

As in the case of a Gd-doped glass (Zghari et al., 2025b), the RIA was also neglected in this model for the Ce³⁺-doped fiber. Indeed, such fiber presented RIA levels comparable to the one of Gd glasses with mean RIA value at 500 nm of ~0.7 dB/cm at 300 Gy dose (Kerboub et al., 2023). Considering similar geometrical effects for the active sample (Zghari et al., 2025b), such mean RIA value during the 300 s irradiation leads to a maximal power loss of about 4%, which is in the same order of magnitude as the RL measurement uncertainties.

In this study, 50 trapping levels were used to reproduce the experimental curves. It should be noted that this number of traps is the minimum required to accurately reproduce the experimental results. It represents a compromise between sufficient energy resolution and ease of parameter selection for the calculation program. Hence, 50 appears to be the best compromise to keep a reasonable number of computational parameters involved in the model.

# 3. Results and discussion

## 3.1. RL and FTSL measurements

Fig. 3 shows an example of the temporal dynamics of light emission from a cerium-doped fiber under irradiation and after irradiation under heating. The irradiation was carried out at a dose rate of 100 mGy/s and at a temperature of 153 K. The curve represents three distinct processes. First, in red, the RL response was measured during the 300 s of X-ray exposure, corresponding to a cumulative dose of 30 Gy at the irradiation temperature $T_{irr} = 153$ K. Next, in blue, the PP signal was measured for 180 s at the same irradiation temperature, after the irradiation was stopped. Finally, in pink, the FTSL signal was recorded by linearly increasing the temperature to 353 K at a heating rate of 5 K/min. This measurement approach was carried out for different dose rates in the
<table><caption>**Table 1**
Values of the parameters used.</caption><thead><tr><th>Parameter</th><th>Status</th><th>Description</th><th>Value for k = 50 (number of electron traps)</th></tr></thead><tbody><tr><td>E<sub>i</sub></td><td>Fixed</td><td>Activation energies of electronic traps</td><td>0.345; 0.36; 0.375; 0.39; 0.405; 0.42; 0.435; 0.45; 0.465; 0.48; 0.495; 0.51; 0.525; 0.54; 0.555; 0.57; 0.585; 0.6; 0.615; 0.63; 0.645; 0.66; 0.675; 0.69; 0.705; 0.72; 0.735; 0.75; 0.765; 0.78; 0.795; 0.81; 0.825; 0.84; 0.855; 0.87; 0.885; 0.91; 0.94; 0.97; 1; 1.03; 1.06; 1.09; 1.12; 1.15; 1.21; 1.24; 1.27; 1.30 eV</td></tr><tr><td>N<sub>i</sub></td><td>Free</td><td>Electron trap concentrations</td><td>5x10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 10<sup>19</sup>; 10<sup>19</sup>; 10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 4x10<sup>18</sup>; 6x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 4x10<sup>19</sup>; 4x10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 4x10<sup>19</sup>; 5x10<sup>19</sup>; 5x10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 3x10<sup>19</sup>; 6x10<sup>19</sup>; 6x10<sup>19</sup>; 6x10<sup>19</sup>; 6x10<sup>19</sup>; 6x10<sup>19</sup> cm<sup>-3</sup></td></tr><tr><td>s<sub>i</sub></td><td>Fixed</td><td>Frequency factors</td><td>10<sup>10</sup> s<sup>-1</sup></td></tr><tr><td>A<sub>ei</sub></td><td>Free</td><td>Ratio between recombination and trapping coefficients</td><td>~10<sup>-3</sup></td></tr><tr><td>A<sub>r</sub></td><td></td><td></td><td></td></tr><tr><td>X</td><td>Fixed</td><td>Electron-hole pair generation rate</td><td>100 mGy (SiO<sub>2</sub>)/s ~ 8.44 × 10<sup>13</sup> cm<sup>-3</sup> s<sup>-1</sup></td></tr><tr><td>M</td><td>Fixed</td><td>Recombination center concentration</td><td>1.17 × 10<sup>19</sup> cm<sup>-3</sup></td></tr><tr><td>k<sub>B</sub></td><td>Fixed</td><td>Boltzmann constant</td><td>8.617330 × 10<sup>-5</sup> eV. K<sup>-1</sup></td></tr><tr><td>t<sub>i</sub></td><td>Fixed</td><td>Irradiation time</td><td>300 s</td></tr><tr><td>t<sub>f</sub></td><td>Fixed</td><td>Phosphorescence time</td><td>180 s</td></tr><tr><td>n<sub>i</sub> &amp; n<sub>c</sub></td><td>Free</td><td>Electron density in N<sub>i</sub> and CB, respectively.</td><td>Evolves over time</td></tr><tr><td>m<sub>j</sub> &amp; m<sub>i</sub></td><td>Free</td><td>Hole density in RC and VB, respectively.</td><td>Evolves over time</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Example of signal response of the Ce<sup>3+</sup>-doped silica fiber for an X-ray dose rate of 100 mGy/s and at 153 K. The RL curve (in red) is followed by phosphorescence one (in blue) and then, by FTSL one (in pink) from 153 K to 353 K with a heating rate of 5 K/min. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

range [50–1000 mGy/s], each time with temperatures varying from 153 K to 353 K.

In Fig. 4(a), for different irradiation temperatures $T_{irr}$, we have plotted the evolution of the RL signal alone (in red in Fig. 3) as a function of the dose rate. For all these temperatures, the RL signal increases linearly with the dose rate. Furthermore, the intensity of the RL signal increases with the irradiation temperature for a constant dose rate, confirming the results observed in (Zghari et al., 2023a) for doped silica rods.

In Fig. 4(b), for different values of $T_{irr}$, we have plotted the evolution of the integrated FTSL signal alone (in pink in Fig. 3) as a function of the X-ray dose. Unlike the RL signal, the FTSL signal decreases as $T_{irr}$ increases. This decrease is explained by the fact that electrons are detrapped by higher thermal energy during irradiation, leaving fewer trapped carriers available for the TL signal.

In Fig. 4(c), the total integrated signal $I_{sum}$, including RL, PP and FTSL (in red, blue, and pink in Fig. 2), is shown as a function of dose for different irradiation temperatures. This total signal $I_{sum}$ is linear with respect to the dose, while being independent of $T_{irr}$. Such a temperature independence can be attributed to the compensation between the increase in the RL signal with temperature and the decrease in the FTSL signal.

## 3.2. Simulation results

Fig. 5 presents an example of the simulation result of the emission signal as a function of time, including RL followed by PP and FTSL. It is observed that the numerical simulations satisfactorily reproduce the experimental data, both during irradiation (RL) and after irradiation has ended (PP + FTSL). This ability of the simulation to match the experimental results was validated for all temperatures and dose rates used in this study. This good agreement was achieved using a single set of parameters, which are summarized in Table 1.

Fig. 6(a) illustrates the variation in the concentration of trapped electrons at the end of irradiation (at 300 s) as a function of the trap energy level, for different irradiation temperatures ranging from 153 to 353 K, under a dose rate of 100 mGy/s. A decrease in the concentration of the shallowest trapped electrons is observed with the increase in the irradiation temperature. This reduction allows for more free electrons to be available for recombining with holes at the recombination centers, but it also leads to a decrease in the number of trapped electrons before the heating phase (FTSL). As a result, the RL signal increases, while the FTSL signal decreases with the irradiation temperature. Moreover, for deeper traps (beyond 0.9 eV), the concentration of electrons increases with irradiation temperature. This phenomenon is due to the stability of the corresponding traps, which act as a reservoir of charge carriers, allowing their retention during successive irradiations. Finally, Fig. 6(b) shows the concentration of trapped electrons at the end of the heating cycle up to 353 K. It is clearly observed that the traps return to a similar state after this step, suggesting that the concentration of recombined electrons between 0.3 and 0.8 eV remains constant, regardless of the irradiation temperature, which results in a constant value of $I_{sum}$.

Fig. 7 represents the simulated $I_{sum}$ as a function of dose at all temperatures, clearly showing the universal linear behavior, which has already been experimentally obtained in this sample (Fig. 4(c)), as well as in Gd-doped silica rods (Zghari et al., 2025b).

## 3.3. Combined RL + OSL measurements: towards a rapid dosimeter independent of temperature

In this section, FTSL has been replaced by OSL, as both processes play a similar role in releasing electrons through the input of thermal or optical energy, respectively. Indeed, for OSL, the measurement was carried out in real-time using a supercontinuum source, the light of which was injected into a transport fiber and reached the sample to release the trapped carriers, yielding supplemental recombination.
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Optical responses for the Ce-doped fiber at different irradiation temperatures ranging from 153 K to 353 K: (a) RL response as a function of dose rate, (b) FTSL integrated response as a function of dose, (c) sum of RL + PP + FTSL integrated responses as a function of dose.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Measured and simulated RL + PP + FTSL signals under X-rays for a dose rate of 100 mGy/s at an irradiation temperature of 153 K. The model uses 50 trap levels and one recombination center.</figcaption></figure>

**Fig. 8** presents the evolution of the combined signal under irradiation, which simultaneously includes both the RL and OSL processes, for six different irradiation temperatures between 153 and 353 K, and dose rates ranging from 0.5 to 2.5 Gy/s. As expected, the measured signal shows a linear behavior with respect to the dose rate and is independent of temperature, within the measurement uncertainties, which are estimated to 6%.

## 4. Conclusion

In this paper, we have investigated the optical emission response of a Ce³⁺-doped silica fiber exposed to X-rays at different irradiation temperatures and different dose rates (RL), as well as the spontaneous signal after such an exposure (PP) and the one under varying the probe temperature (FTSL). Using an experimental fibered setup that allowed the study of the three fundamental optical processes (RL, PP and FTSL), and integrating those signals over time, the dose measurements have been shown to remain independent of both dose rate and temperature, for cumulated dose at least up to 30 Gy with the tested fiber. A standard model has been used to fit the emission signal data, explaining the physical processes and allowing the extraction of the trapped carriers' populations. The results show that the temperature independence of the integrated intensities of the three processes can be interpreted by the thermal detrapping of charge carriers, leading to an increase in the RL signal, which is counterbalanced by a diminishing FTSL signal at higher temperature.

Our approach consisting in the integrated measurement of the three processes, already successfully applied to a Gd³⁺-doped silica rod in a previous paper (Zghari et al., 2025b), is now validated for a Ce³⁺-doped fiber in a reproducible manner. Moreover, replacing FTSL with OSL gives a linear integrated signal as a function of dose rate and this signal is almost constant at different irradiation temperatures, which opens perspectives for temperature-independent real-time dosimetry through a highly flexible, reliable and sustainable setup.

## CRediT authorship contribution statement

**Ismail Zghari:** Writing – review & editing, Writing – original draft, Visualization, Validation, Software, Methodology, Investigation, Formal
<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Trapped electron concentration as a function of energy level, resulting from the simulation at different irradiation temperatures ($T_{irr}$) (a) at the end of the irradiation (at 300 s) and (b) at the end of heating to 353 K. The dose rate is 100 mGy/s during irradiation (accumulated dose of 30 Gy).</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 7.** Simulated $I_{sum}$ signal as a function of dose at different temperatures.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Fig. 8.** Combined integral RL and OSL signals as a function of dose rate at different irradiation temperatures.</figcaption></figure>

analysis, Data curation, Conceptualization. **Hicham El Hamzaoui:** Writing – review & editing, Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Adriana Morana:** Methodology, Investigation. **Youcef Ouerdane:**

**Methodology, Investigation.** **Bruno Capoen:** Writing – review & editing, Visualization, Validation, Methodology, Investigation, Formal analysis, Conceptualization. **Sylvain Girard:** Writing – review & editing, Validation, Methodology. **Aziz Boukenter:** Project administration, Methodology, Funding acquisition. **Mohamed Bouazaoui:** Writing – review & editing, Visualization, Validation, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization.

## Funding

This work was supported in part by the Agence Nationale de la Recherche through the project FIDELIO [ANR-20-CE19-0024] and LABEX CEMPI [ANR-11-LABX-0007]. This work was also carried out within the framework of the Contrat de Plan Etat-Region (CPER) WaveTech@HdF, which is supported by the Ministry of Higher Education and Research, the Hauts-de-France (HdF) Regional council, the Lille European Metropolis (MEL), the Institute of Physics of the French National Centre for Scientific Research (CNRS) and the European Regional Development Fund (ERDF).

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

This work was also supported by the IRCICA Institute and the FiberTech Lille platform of the University of Lille.

## Data availability

Data will be made available on request.

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