Effect of Mg on the Structural, Optical and Thermoluminescence Properties of Li3Al3(BO3)4: Shift in Main Glow Peak

The doping of magnesium on lithium aluminium borate phosphor is reported in this study. A solid-state sintering technique was employed as the borate samples were synthesized. This report focuses on the structural, optical, thermoluminescence, and kinetic analyses of the main glow peak. The structural properties of lithium aluminium borates improved due to the magnesium dopants used. Differences in the crystallite size and particle size were 38.85–67.35 nm and 50–60 nm, respectively, and these results were obtained from the analyzed X-ray diffractogram and scanning electron spectroscopy. The energy band gaps obtained from the direct transition of borate phosphor materials were within the range of 3.00–4.40 eV, and the doped samples gave a higher energy band gap. A decrease in the TGA (%) exhibited a weight loss or water loss for the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate materials. The glow curve measured at a heat rate of 1 °C·s−1 after irradiation to 50 Gy revealed four peaks related to the magnesium doped lithium aluminium borate. The main glow peak was observed at 86 °C. Activation energy was extracted from the main glow peak by using kinetic analysis which involves the initial rise, deconvolution, and variable heating rate approach, and it was approximately 0.67 ± 0.03 eV. A shift in the main glow peak curve from 86 to 110 °C was recognized for the magnesium-doped lithium aluminium borate when it was irradiated from 1 to 300 Gy.


Introduction
The structural, thermal, and chemical stability of lithium aluminum borate materials have encouraged their usein radiation protection, laser devices, scintillators, and thermoluminescence studies [1][2][3][4][5]. These properties are strongly associated with the structure of materials and are of the utmost interest to researchers because they are necessary for dosimetry.
The structural behavior of anionic groups of borate composites which consist of boron and oxygen atoms is important regarding the discussion of thermoluminescence dosimetry (TLDs). Some classifications of borate crystal structures described [6][7][8][9] and reviewed in various publications [10][11][12][13][14][15][16] are referred to as boron and oxygen atom coordinates which are interconnected in triangular (BO 3 ) and tetrahedral (BO 4 ) borates. Such an alliance is associated with joint oxygen atoms which constitute the fundamental building blocks

Experimental Route
The solid-state sintering technique was adopted for the synthesis of lithium aluminium borate (Li 3 Al 3 (BO 3 ) 4 ) samples. Analytical grade precursors (98%) from Sigma Aldrich were used at a given mass of 1.64 g for lithium carbonate, 3.46 g for aluminium hydroxide, and 3.67 g for boric acid. The precursors were mixed in agitate mortar by adding 50 mL of deionized water, which was then stirredat 40 revolutions per minute for 30 min to obtain a homogeneous distribution of stochiometric compounds. Other baths were obtained by adding various masses of 0.34, 0.76, 1.10, 1.40, and 1.78 mg magnesium dopant, which corresponded to mole concentrations of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, respectively. Then, the resultant solution was heated and dried on a hot plate at about 100 • C inside a fume chamber for about 30 min. The obtained mixed material was then heated in a muffle furnace (Searchtech Instruments SXL) at 950 • C for a period of 5 h. The samples were removed from the furnace when they were at a molten state from; next, theywere exposed and allowed to cool to an ambient temperature. The hard whitish ceramic materials were crushed into a fine powder before they were placed back into the muffle furnace and further annealed to a temperature of 300 • C for an hour. The high temperature annealing removed water molecules and carbon dioxide which helped form a stable material, and further annealing was done on the powdered samples before further studies were carried out to improve its structural and luminescence properties.
The morphological structure was determined using a scanning electron microscope (ZEISS GeminiSEM 500, NanoFab Microscopy, Gaithersburg, MD 20899-6201, USA). The grain size arrangement from the obtained morphological structure was also analyzed with imagej freeware. An X-ray diffractometer (AXS D8 diffractometer, Bruker, Allentown, PA, USA) was used to study the crystal structure. A visible spectrum was used to determine the UV-vis-NIR spectra (UV-1800 Shimadzu UV spectrophotometer, Mettler-Toledo, Columbus, OH 43240, USA) from which the optical properties were obtained. Thermal analysis (TG-DTA and TMA Rigaku Evo plus II, Tokyo, Japan) was used to study the weight loss of the compounds. Thermoluminescence of all the samples was measured using an A RISØ TL/OSL DA-20 Luminescence Reader (DTU Risø Campus, DK-4000 Roskilde, Denmark). The samples were properly irradiated using a 90 Sr/ 90 Y β source at a time rate of 0.1 Gy/s. Luminescence was recognized using an EM 9235QB Photomultiplier tube that was fitted through a 7.0 mm Hoya U-340 filter. All the measurements that were detected were created at a heating rate of 1 • C/s. Kinetic analyses were also studied based on the obtained TL results.

Structural Analysis
XRD plots at a 2θ angle from 10 to 75 • that were designed for both the undoped concentrations and the various concentrations of magnesium doped lithium aluminium borate phosphor and are shown in Figure 1. Peak intensities were observed from all the samples, but they appear to be more intense at higher concentrations of the magnesium doped (0.4% and 0.5%) samples. The 2θ value from the indicated intensity peaks at 17 corresponded to mole concentrations of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, respectively. Then, the resultant solution was heated and dried on a hot plate at about 100 °C inside a fume chamber for about 30 min. The obtained mixed material was then heated in a muffle furnace (Searchtech Instruments SXL) at 950 °C for a period of 5 h. The samples were removed from the furnace when they were at a molten state from; next, theywere exposed and allowed to cool to an ambient temperature. The hard whitish ceramic materials were crushed into a fine powder before they were placed back into the muffle furnace and further annealed to a temperature of 300 °C for an hour. The high temperature annealing removed water molecules and carbon dioxide which helped form a stable material, and further annealing was done on the powdered samples before further studies were carried out to improve its structural and luminescence properties. The morphological structure was determined using a scanning electron microscope (ZEISS GeminiSEM 500,NanoFab Microscopy, Gaithersburg, MD 20899-6201). The grain size arrangement from the obtained morphological structure was also analyzed with imagej freeware. An X-ray diffractometer (AXS D8 diffractometer, Bruker, USA) was used to study the crystal structure. A visible spectrum was used to determine the UV-vis-NIR spectra (UV-1800 Shimadzu UV spectrophotometer,Mettler-Toledo, Columbus, OH 43240) from which the optical properties were obtained. Thermal analysis (TG-DTA and TMA Rigaku Evo plus II, Japan) was used to study the weight loss of the compounds. Thermoluminescence of all the samples was measured using an A RISØ TL/OSL DA-20 Luminescence Reader (DTU Risø Campus, DK-4000 Roskilde). The samples were properly irradiated using a 90 Sr/ 90 Y β source at a time rate of 0.1 Gy/s. Luminescence was recognized using an EM 9235QB Photomultiplier tube that was fitted through a 7.0 mm Hoya U-340 filter. All the measurements that were detected were created at a heating rate of 1 °C/s. Kinetic analyses were also studied based on the obtained TL results.

Structural Analysis
XRD plots at a 2θ angle from 10 to 75°that were designed for both the undoped concentrations and the various concentrations of magnesium doped lithium aluminium borate phosphor and are shown in Figure 1. Peak intensities were observed from all the samples, but they appear to be more intense at higher concentrations of the magnesium doped   The corresponding crystallite sizes (S) for all the samples were calculated based on the most consequential intense peak at a 2θ angle of 17.06 ± 0.03 • by using Debye Scherrer's equation [32]: where λ = 1.5406Å is the wavelength for the X-ray target; θ is Bragg's angle; and β is the full width at half maximum intensity. The calculated crystallite size of the undoped lithium aluminium borate was 53.95 nm, as shown in Table 1. There was a gradual increase in the crystallite size from 0.1% to 0.5% mole concentration for the Mg-doped lithium aluminium borate, as shown in Table 1. The crystallite size for concentrations of 0.1%, 0.2%, and 0.3% Mg-doped lithium aluminium borate were less than the value of 53.95 nm for the undoped lithium aluminium borate, while the 0.4% and 0.5% mole concentrations were greater than 53.95 nm. The regular crystal size increased as the mole concentration of the magnesium dopant increased. A saturation phase was reached just before 0.4% to 0.5% mole concentrations, and a further increase resulted in an increase in the crystallite size which was observed to be greater than the undoped material of lithium aluminium borate. This could be as a result of the reaction as it was no longer effective during the mix up.

Morphology Survey
Surface morphological surveys for the undoped and the 0.1% doped lithium aluminium borate samples were carried out using the SEM image shown in Figure 2. The grains spread irregularly over the entire surface for both samples. The undoped sample was composed of some spongy clusters, while the 0.1% magnesium doped lithium aluminium borate showed aggregates with a bigger surface area which was composed of tiny particles that were smaller than that of the undoped samples.
The corresponding crystallite sizes (S) for all the samples were calculated based on the most consequential intense peak at a 2ϴ angle of 17.06 ± 0.03° by using Debye Scherrer's equation [32]: where λ = 1.5406Å is the wavelength for the X-ray target; θ is Bragg's angle; and β is the full width at half maximum intensity. The calculated crystallite size of the undoped lithium aluminium borate was 53.95 nm, as shown in Table 1. There was a gradual increase in the crystallite size from 0.1% to 0.5% mole concentration for the Mg-doped lithium aluminium borate, as shown in Table 1. The crystallite size for concentrations of 0.1%, 0.2%, and 0.3% Mg-doped lithium aluminium borate were less than the value of 53.95 nm for the undoped lithium aluminium borate, while the 0.4% and 0.5% mole concentrations were greater than 53.95 nm. The regular crystal size increased as the mole concentration of the magnesium dopant increased. A saturation phase was reached just before 0.4% to 0.5% mole concentrations, and a further increase resulted in an increase in the crystallite size which was observed to be greater than the undoped material of lithium aluminium borate. This could be as a result of the reaction as it was no longer effective during the mix up.

Morphology Survey
Surface morphological surveys for the undoped and the 0.1% doped lithium aluminium borate samples were carried out using the SEM image shown in Figure 2. The grains spread irregularly over the entire surface for both samples. The undoped sample was composed of some spongy clusters, while the 0.1% magnesium doped lithium aluminium borate showed aggregates with a bigger surface area which was composed of tiny particles that were smaller than that of the undoped samples. Size distributions from the cross-sectional surface morphology of the samples were further studied by usingimagej software which detected grain sizes that were presented as histogram plots, as shown in Figure 3. The undoped samples of lithium aluminium borate grain sizes were obtained from 80 to 220 nm with a maximum count of 19. The bar with the highest count was observed at grain sizesbetween 140 and 160 nm, while other bars appeared to decrease on either side of it. Magnesium (0.1%) doped lithium aluminium borate grain sizes were also obtained in a range from 40 to 140 nm with the highest count of 15. The highest bar, which indicates the highest number in the distribution, was observed to be at a grain size in the range of 50 to 60 nm. The grain size display of the magnesiumdoped lithium aluminium borate was smaller than the result obtained from the distribution.
Materials with size distributions in the range from 75 nm to 200 nm [33] are reported to have unique advantage when they are used as radiative and optical instruments.
borate grain sizes were obtained from 80 to 220 nm with a maximum count of 19. The bar with the highest count was observed at grain sizesbetween 140 and 160 nm,while other bars appeared to decrease on either side of it. Magnesium (0.1%) doped lithium aluminium borate grain sizes were also obtained in a range from 40 to 140 nm with the highest count of 15. The highest bar, which indicates the highest number in the distribution, was observed to be at a grain size in the range of 50 to 60 nm. The grain size display of the magnesium-doped lithium aluminium borate was smaller than the result obtained from the distribution. Materials with size distributions in the range from 75 nm to 200 nm [33]are reported to have unique advantage when they are used as radiative and optical instruments.

Optical Properties
The energy required to stimulate an electron through a gap between the valence and the conduction band (also known as the energy band gap) and the interaction of the incident photon determines the optical properties of a phosphor material. These are important features of any semiconductor or phosphor material that is studied to determine structural, luminescence, thermal, and electronic properties. Figure 4 shows the absorbance plots for both the undoped concentrations and the various concentrations of magnesium-doped lithium aluminium borate. The absorbance of the materials was considered within the range of visible spectrum from 300 to 800 nm. The absorption spectrums observed were lines of slight peaks with absorbance that is high at the short wavelength and low at the long wavelength. The undoped lithium aluminium borate gave the highest absorbancewhen compared with the doped samples, as indicated in the plot in Figure 4. The doped samples of magnesium lithium aluminium borate decreased from0.1% to 0.3% mole percent concentration and increased from 0.4% to 0.5% (not shown). This shows that different minute values of magnesium-doped samples of lithium aluminium borate resulted in a slight decrease in the absorbance, which obtained saturation at 0.3% mole concentration.

Optical Properties
The energy required to stimulate an electron through a gap between the valence and the conduction band (also known as the energy band gap) and the interaction of the incident photon determines the optical properties of a phosphor material. These are important features of any semiconductor or phosphor material that is studied to determine structural, luminescence, thermal, and electronic properties. Figure 4 shows the absorbance plots for both the undoped concentrations and the various concentrations of magnesium-doped lithium aluminium borate. The absorbance of the materials was considered within the range of visible spectrum from 300 to 800 nm. The absorption spectrums observed were lines of slight peaks with absorbance that is high at the short wavelength and low at the long wavelength. The undoped lithium aluminium borate gave the highest absorbancewhen compared with the doped samples, as indicated in the plot in Figure 4. The doped samples of magnesium lithium aluminium borate decreased from0.1% to 0.3% mole percent concentration and increased from 0.4% to 0.5% (not shown). This shows that different minute values of magnesium-doped samples of lithium aluminium borate resulted in a slight decrease in the absorbance, which obtained saturation at 0.3% mole concentration. The band gap energy plot for each synthesized magnesium-doped lithium aluminium borate phosphor material is shown in Figure 5. This was achieved by using the stated equation [34]: where the photon energy, transition probability, absorption coefficient, and Planck' s constant are represented in the equation as hv, A, α, and h, respectively. The exponent n is the transition during the absorption process which can be values 1/2, 3/2, 2, and 3 which cat- The band gap energy plot for each synthesized magnesium-doped lithium aluminium borate phosphor material is shown in Figure 5. This was achieved by using the stated equation [34]: where the photon energy, transition probability, absorption coefficient, and Planck' s constant are represented in the equation as hv, A, α, and h, respectively. The exponent n is the transition during the absorption process which can be values 1/2, 3/2, 2, and 3 which categorically represent the direct allowed, direct forbidden, indirect allowed, and indirect forbidden transition state. The linear extrapolation of the plots from the tail end to where it meets a point on the horizontal axis is denoted as the band gap energy. The direct allowed transition state from the energy band gaps obtained were observed at points on the horizontal axis in the plot in Figure 5 [5,35]. The use of Mg as a dopant increased the band gap energy of lithium aluminium borate phosphor, which makes it a good semiconductor that will display a luminescence phenomenon when it is used for dosimetry [5]. The majority of materials used for dosimetric applications have a high energy band gap. Based on reports, TL phosphorsthat are useful in radiation dosimetry, such as Al 2 O 3 and Li 2 B 4 O 7 , have band gap energies of 9.5 eV and 7.5 eV, respectively [36]. The highest energy band gap ever obtained from doped lithium aluminium borate phosphor was 4.4 eV [5], which is also similar to our result.

Thermal Gravimetric Analysis (TGA)
Thermal gravimetric analyses of the powdered samples of the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate were studied within a temperature range of 0 to 930°C, as shown in Figure 6. A sharp decrease in the TGA (%) peak which exhibited a weight loss for the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate materials was observed at temperatures of 611, 830, and 308 °C, respectively. However, the 0.1% Mg-doped sample had a gradual decrease which started from the origin to the temperature of 830 °C where the sharp drop was seen. The samples will show some form of stability when used in any form of application at such a range observed before a drastic weight loss. María et al. [37,38] reported that weight loss or water loss during the thermal treatment of samples was a result of the decomposition of the boric acid (H3BO3 to B2O3) used during its preparation.

Thermal Gravimetric Analysis (TGA)
Thermal gravimetric analyses of the powdered samples of the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate were studied within a temperature range of 0 to 930 • C, as shown in Figure 6. A sharp decrease in the TGA (%) peak which exhibited a weight loss for the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate materials was observed at temperatures of 611, 830, and 308 • C, respectively. However, the 0.1% Mg-doped sample had a gradual decrease which started from the origin to the temperature of 830 • C where the sharp drop was seen. The samples will show some form of stability when used in any form of application at such a range observed before a drastic weight loss. María et al. [37,38] reported that weight loss or water loss during the thermal treatment of samples was a result of the decomposition of the boric acid (H 3 BO 3 to B 2 O 3 ) used during its preparation. materials was observed at temperatures of 611, 830, and 308 °C, respectively. However, the 0.1% Mg-doped sample had a gradual decrease which started from the origin to the temperature of 830 °C where the sharp drop was seen. The samples will show some form of stability when used in any form of application at such a range observed before a drastic weight loss. María et al. [37,38] reported that weight loss or water loss during the thermal treatment of samples was a result of the decomposition of the boric acid (H3BO3 to B2O3) used during its preparation.

Thermoluminescence
Semiconductor materials undergo a stimulated process known as thermoluminescence (TL) after the absorption of energy from ionizing radiation [35]. TL was used to

Thermoluminescence
Semiconductor materials undergo a stimulated process known as thermoluminescence (TL) after the absorption of energy from ionizing radiation [35]. TL was used to study how the phosphor materials were able to store the absorbed energy for a given period before discharging it in the form of visible light. The level of defect caused by a phosphor material also determines the TL intensity, which is usually displayed as a glow curve.
The glow curves obtained for the undoped samplesand the magnesium-doped lithium aluminium borate were heated from 0 to 500 • C, as shown in Figure 7. The plots were considered to be a very low dose rate (5 Gy) with major peaks at 86 • C as well as minor peaks observed at a higher temperature point from the glow curves. The TL glow curve for the 0.1% mole Mg-doped lithium aluminium borate was irradiated at 50 Gy after it was thermally cleaned and is shown in Figure 8. Thermal cleaning was done to eliminate the minor glow peaks that were present alongside the high temperature region. The inset in Figure 8 represents the logarithmic glow curve plot which was used to identify supplementary peaks other than the foremost glow peak. lithium aluminium borate resulted in a decrease in its optical energy band gap. The 0.2% and 0.3% Mg-doped lithium aluminium borate glow curves were similar because there were few differences compared to the crystallite size results and the optical energy band gap results reported earlier. Further research was carried out regarding the dosimetric properties by using only the 0.1% mole concentration of Mg-doped lithium aluminium borate because its high TL intensity resulted in a higher sensitivity of the material used for different dosimetric applications. The TL glow curve for the 0.1% mole Mg-doped lithium aluminium borate was irradiated at 50 Gy after it was thermally cleaned and is shown in Figure 8. Thermal cleaning was done to eliminate the minor glow peaks that were present alongside the high temperature region. The inset in Figure 8 represents the logarithmic glow curve plot which was used to identify supplementary peaks other than the foremost glow peak.

Kinetic Analysis
The activation energy, frequency factors, and order of kinetics of lithium aluminum borate doped with 0.1 percent magnesium were evaluated further by adopting the initial rise, variable heating rate, and deconvolution approach to extract data associated with the charge transfer process from the main glow peak. The glow curve was not isolated; therefore, these approaches were confirmed to be the only ones that were appropriate for the

Kinetic Analysis
The activation energy, frequency factors, and order of kinetics of lithium aluminum borate doped with 0.1 percent magnesium were evaluated further by adopting the initial rise, variable heating rate, and deconvolution approach to extract data associated with the charge transfer process from the main glow peak. The glow curve was not isolated; therefore, these approaches were confirmed to be the only ones that were appropriate for the analysis.

Kinetic Analysis
The activation energy, frequency factors, and order of kinetics of lithium aluminum borate doped with 0.1 percent magnesium were evaluated further by adopting the initial rise, variable heating rate, and deconvolution approach to extract data associated with Molecules 2023, 28, 504 9 of 13 the charge transfer process from the main glow peak. The glow curve was not isolated; therefore, these approaches were confirmed to be the only ones that were appropriate for the analysis.

Initial Rise Method
The 0.1% magnesium-doped lithium aluminum borate materials were irradiated at a low dose of 50 Gyand were studied using the initial rise approach which was only applied at the lower peak temperature region. The plot of the natural log of TL intensity versus 1/kT revealed the activation energy E of the sample of lithium aluminium borate doped with magnesium. The experimental plot revealed the activation energy from the given equation.
where k, E, T, and C represent the Boltzmann constant, activation energy, temperature, and constant [39]. The plots of the log of TL versus 1/kT for the Mg-doped lithium aluminum borate are shown in Figure 10, and the results from the analysis determined that the activation energy was 0.65 ± 0.01 eV.
Molecules 2021, 26, x FOR PEER REVIEW 10 of 14 1/kT revealed the activation energy E of the sample of lithium aluminium borate doped with magnesium. The experimental plot revealed the activation energy from the given equation.
where k, E, T, and C represent the Boltzmann constant, activation energy, temperature, and constant [39]. The plots of the log of TL versus 1/kT for the Mg-doped lithium aluminum borate are shown in Figure 10, and the results from the analysis determined that the activation energy was 0.65 ± 0.01 eV.

Curve Deconvolution
As shown in Figure 11, the curve deconvolution method was applied to the peak of the magnesium-doped lithium aluminium borate sample. Evaluation of the glow curve was achieved using the general order equation given by Kitis [40].
where Im, Tm, and b stand for the peak maximum intensity, the temperature at its peak maximum position, and the kinetic order. All other parameters in this equation have already been established. The figure of merit (FOM) was used to evaluate the quality of the glow curve fit, which was specified in the preceding equation as: where Efit and Dexp are the fitted data and experimental data, respectively. If the FOM is less than 3.5 percent, it is assumed that the fit is satisfactory [41]. The activation energy, frequency factor, and order of kinetic for the samples of Mg-doped lithium aluminum borate were estimated to be 0.69 + 0.01 eV, 1.72 × 10 9 •s −1 , and 1.32, respectively. The obtained value for the activation energy was close to the one from the initial rise approach. The fit was considered adequate because the figure of merit for the Mg-doped lithium aluminum borate was 1.49%.

Curve Deconvolution
As shown in Figure 11, the curve deconvolution method was applied to the peak of the magnesium-doped lithium aluminium borate sample. Evaluation of the glow curve was achieved using the general order equation given by Kitis [40].
where Im, Tm, and b stand for the peak maximum intensity, the temperature at its peak maximum position, and the kinetic order. All other parameters in this equation have already been established. The figure of merit (FOM) was used to evaluate the quality of the glow curve fit, which was specified in the preceding equation as: where E fit and D exp are the fitted data and experimental data, respectively. If the FOM is less than 3.5 percent, it is assumed that the fit is satisfactory [41]. The activation energy, frequency factor, and order of kinetic for the samples of Mg-doped lithium aluminum borate were estimated to be 0.69 + 0.01 eV, 1.72 × 10 9 ·s −1 , and 1.32, respectively. The obtained value for the activation energy was close to the one from the initial rise approach.
The fit was considered adequate because the figure of merit for the Mg-doped lithium aluminum borate was 1.49%.

Variable Heating Rate (VHR) Method
The activation energy was determined by changing the glow curve heating rate. The analysis was based on the temperature alteration at intensity peaks (Tm) with various heat rates (0.2, 0.4, 0.6, and 0.8 °Cs −1 ) from a specified range that was less than one. The following equation was used to assess the data.
where the frequency factor is represented as s and all other parameters have already been discussed [37]. The activation energy was 0.70 + 0.03 eV, and this was based on the straight line plot of In(   Figure 13 illustrates the radiation dose-response of the magnesium-doped lithium aluminum borate materials at doses that ranged from 1 to 300 Gy. An increase in the TL main glow peak was detected at different levels of radiation exposure to the materials. A shift in the glow peak from 86 °C at a low radiation dose to 110 °C at a high radiation dose

Variable Heating Rate (VHR) Method
The activation energy was determined by changing the glow curve heating rate. The analysis was based on the temperature alteration at intensity peaks (Tm) with various heat rates (0.2, 0.4, 0.6, and 0.8 • Cs −1 ) from a specified range that was less than one. The following equation was used to assess the data.
where the frequency factor is represented as s and all other parameters have already been discussed [37]. The activation energy was 0.70 + 0.03 eV, and this was based on the straight line plot of In(T 2 m /β) versus (1/kTm) in Figure 12. The frequency factor s was estimated based on the intercept as given in In(E/sk) when the extrapolation of 1/Tm was zero. The frequency factor s for the Mg-doped lithium aluminum borate yielded a value of 4.3 × 10 8 s −1 .

Variable Heating Rate (VHR) Method
The activation energy was determined by changing the glow curve heating rate. The analysis was based on the temperature alteration at intensity peaks (Tm) with various heat rates (0.2, 0.4, 0.6, and 0.8 °Cs −1 ) from a specified range that was less than one. The following equation was used to assess the data.
where the frequency factor is represented as s and all other parameters have already been discussed [37]. The activation energy was 0.70 + 0.03 eV, and this was based on the straight line plot of In(   Figure 13 illustrates the radiation dose-response of the magnesium-doped lithium aluminum borate materials at doses that ranged from 1 to 300 Gy. An increase in the TL main glow peak was detected at different levels of radiation exposure to the materials. A shift in the glow peak from 86 °C at a low radiation dose to 110 °C at a high radiation dose  Figure 13 illustrates the radiation dose-response of the magnesium-doped lithium aluminum borate materials at doses that ranged from 1 to 300 Gy. An increase in the TL main glow peak was detected at different levels of radiation exposure to the materials. A shift in the glow peak from 86 • C at a low radiation dose to 110 • C at a high radiation dose was observed as shown in the plot, and both peak temperatures had an almost equal intensity at 180 Gy. The reason for this is unknown; however, it could be due to structural deformation caused by the addition of the magnesium dopant into the compound of lithium aluminium borate.

Dose-Response
was observed as shown in the plot, and both peak temperatures had an almost equal intensity at 180 Gy. The reason for this is unknown; however, it could be due to structural deformation caused by the addition of the magnesium dopant into the compound of lithium aluminium borate. Temperature ( o C) TL intensity (a.u.) The stated mathematical equation below was used to express the dose-response:

Li 3 Al 3 (BO 3 ) 4 :Mg
where TL is the highest intensity, D is the recorded dose, and a and b are measured constants [39]. The slope obtained from the plot of the log of TL versus the log of D is equal to b, and the straight line depicts the linear dose-response for the Mg-doped lithium aluminium borate sample, as shown in Figure 14. The linear dose-response of Mg-doped lithium aluminium borate phosphor was observed in the given plot. As the observation shows, calibrations are not needed because the linear TL response for phosphor materials is useful and convenient fordosimetric materials for personnel and environmental monitoring.  The stated mathematical equation below was used to express the dose-response: where TL is the highest intensity, D is the recorded dose, and a and b are measured constants [39]. The slope obtained from the plot of the log of TL versus the log of D is equal to b, and the straight line depicts the linear dose-response for the Mg-doped lithium aluminium borate sample, as shown in Figure 14. The linear dose-response of Mg-doped lithium aluminium borate phosphor was observed in the given plot. As the observation shows, calibrations are not needed because the linear TL response for phosphor materials is useful and convenient fordosimetric materials for personnel and environmental monitoring.
was observed as shown in the plot, and both peak temperatures had an almost equal intensity at 180 Gy. The reason for this is unknown; however, it could be due to structural deformation caused by the addition of the magnesium dopant into the compound of lithium aluminium borate.  1Gy  10Gy  20Gy  40Gy  60Gy  80Gy  100Gy  150Gy  180Gy  200Gy  220Gy  250Gy  280Gy  300Gy Temperature ( o C) TL intensity (a.u.)   (7) where TL is the highest intensity, D is the recorded dose, and a and b are measured constants [39]. The slope obtained from the plot of the log of TL versus the log of D is equal to b, and the straight line depicts the linear dose-response for the Mg-doped lithium aluminium borate sample, as shown in Figure 14. The linear dose-response of Mg-doped lithium aluminium borate phosphor was observed in the given plot. As the observation shows, calibrations are not needed because the linear TL response for phosphor materials is useful and convenient fordosimetric materials for personnel and environmental monitoring.

Conclusions
The influence of magnesium doping on the structural, optical, and thermoluminescence of lithium aluminium borate was studied. A solid-state sintering technique was employed in the synthesis of borate samples. The crystallite and particle sizes obtained from the doped and undoped samples varied when they were compared. The optical absorbance and the energy band gap obtained from the direct transition varied for both the Mn-doped and the undoped lithium aluminium borate phosphor materials. The decrease in the TGA (%) peak exhibited a weight loss for the undoped, 0.1% Mn, and 0.3% Mn-doped lithium aluminium borate materials. The main glow peak was observed at 86 • C at a heat rate of 1 • C·s −1 after irradiation to 50 Gyalongside three other peaks which occurred at an exalted temperature level of the glow curve. The activation energy from the main glow peak was studied using initial rise, deconvolution, and variable heating rate approaches. The results obtained were consistent based on the methods that were adopted. A shift in the glow peak from 86 to 110 • C was observed as Mg-doped lithium aluminium borate material was exposed to radiation doses from 1 to 300 Gy. This implies that the structural performance of the lithium aluminium borate material improved due to the use of magnesium as a dopant and thatthe increase in TL sensitivity regarding the range of dose also improved.