Promising reddish-orange light as Eu3+ incorporated in zinc-borosilicate glass derived from the waste glass bottle

Eu3+ incorporated zinc-borosilicate glass was synthesized using melt-quenching method. XRD and FTIR verified the amorphous nature of the samples. The absorption spectra indicate the Eu3+ ions in the UV-visible region at ∼394 nm. The direct and indirect band gap decrease from 5.152 eV to 5.082 eV and 4.133 eV to 3.837 eV, respectively. Meanwhile, the refractive index decrease from 2.145 to 2.202, while the Urbach energy ranges from 0.682 eV to 0.733 eV. All the samples have a good transmission percentage at 70–75%. Under the excitation of 400 nm, the intensity of the PL spectra increased when the Eu3+ dopant increased. The optimum content for Eu3+ incorporated ZnO–B2O3–GB glass is 3 wt.% among the other Eu3+ content (0, 1, and 2 wt.%) in this work. The reddish-orange emission at 612 nm (5D0 → 7F2) indicates the most intense emission and the CIE chromaticity coordinates imply in the reddish-orange region.


Introduction
Across the years, luminescent materials have been effectively employed in optoelectronics, photonics, and solid-state lasers.Due to their energy consumption, brightness, long lifetime, and being environmentally friendly, researchers worldwide focus on optoelectronic applications, such as light-emitting diode (LED), solidstate lighting, and fluorescent display devices [1,2].In addition, luminescent materials have a wide application which also can be applied in biosensing and bioimaging, phototherapy, data storage, security technologies, optical temperature sensors, and fluorescent thermometers [3][4][5][6][7].The luminous material's capabilities are deeply controlled by the active centres, the host material, and their interaction [8].Meanwhile, glass is critical for optical material applications due to its excellent transparency in the visible region.The typical material fabricating glass bottles is soda-lime-silica, consisting of 70.5% SiO 2 , 12.5% Na 2 O, 11.3% CaO, and 2.8% Al 2 O 3 [9,10] .Unfortunately, waste glass bottles are one of the toughest to recycle [11].Therefore, this work uses the waste glass bottles as the SiO 2 source to fabricate zinc-borosilicate glass (ZnO-B 2 O 3 -GB).Glasses made of zinc-borosilicate are noteworthy for their thermal shock resistance, strong elastic modulus, chemical resistance, and piezoelectric characteristics [12].Nevertheless, zinc-borosilicate glass's low energy absorption rates have restricted its applicability.Introducing rareearth ions into the host glass is one method for resolving this issue.
The glass matrix incorporated with rare-earth ions exhibits outstanding optical properties, including excellent resistance to laser amplification and high quantum efficiency [13].Eu 3+ ions stand out among the rareearth ions as an activator with bright orange and red emissions due to the 4f →4f electronic transition across the 5 D 0 → 7 F J transition, where J = 0 to 6.In addition, Eu 3+ ions are also utilized in various technological uses due to their reputed electric dipole transition 5 D 0 → 7 F 2 ( ∼ 611 nm), resulting in a consistent perfect red lightemitting centre for the display system [14,15].From the literature, the chemical environment affects the intensity of this hypersensitive electric dipole transition, whereas the magnetic dipole transition 5 D 0 → 7 F 1 ( ∼ 593 nm) is unaffected by the local ligand field [16].
To the best of our knowledge, the zinc-borosilicate glass system incorporated rare earth has been extensively explored for its photoluminescence capabilities.This paper describes the synthesis of Eu 3+ incorporated zinc-borosilicate glass derived from waste glass bottles via the melt-quenching method.In addition, the effect of the Eu 3+ dopant on the structural, optical, and luminescence properties was explored.The novel material developed in this work is prospective to be utilized as a reddish-orange phosphor material in optoelectronic devices such as LEDs.

Samples preparation
The melt-quenching method was utilized to synthesize the europium incorporated zinc-borosilicate glass, with the empirical formula, [Eu 2 O 3 ] x [(ZnO) 0.5 (B 2 O 3 ) 0.1 (GB) 0.4 ] 1−x , where x = 0, 0.01, 0.02, 0.03 in weight percent as presented in Table 1.The raw materials selected were zinc oxide (Sigma-Aldrich, 99.9%), boron oxide (Acros Organics, 98%), waste transparent glass bottle as the source of SiO 2 , and europium (III) oxide 3 (Alfa Aesar, 99.99%) powders.The cleaned glass bottles (GB) were first crushed using a plunger, ground with a mortar and pestle, and then sieved into 45 µm to obtain a fine powder.After that, the obtained glass bottle powder, zinc oxide, boron oxide, and europium (III) oxide powder were mixed and milled to get homogeneous powders.Next, the alumina crucible with the mixture was melted at 1300 °C at 10 °C/min and held for 2 h at a hightemperature electrical furnace.Meanwhile, to eliminate bubbles from the glass melt, the crucible was swirled twice during the melting process before the quenching process.Next, the glass melts were quenched in another furnace using a prepared stainless-steel mold and then annealed for an hour at 400 °C to eliminate any tiny bubbles in the glass and prevent it from thermal shock.

Characterization
In the present work, the glassy phases of the samples were determined by X-ray diffraction (XRD) through PANalytical (Philips) X' Pert Pro PW3050/6 in powders form via Ni-filtered Cu-Kα radiation.The 2θ scans were performed which scanned at 2θ, which is 20°to 80°.Besides, the molecular vibrations of the samples were investigated via Perkin Elmer Spectrum Two Fourier transform spectrometer (FTIR) with a wavenumber of 4000-400 cm −1 .Meanwhile, the optical absorbance and reflectance of the glass sample were determined using UV-Vis spectroscopy with a transmission range of 220-1000 nm.Likewise, the photoluminescence excitation (PLE) the photoluminescence emission was determined using a photoluminescence spectrometer, model Perkin Elmer LS 55.Finally, the CIE chromaticity coordination of the sample was calculated using

X-ray diffraction (XRD) analysis
Figure 1 indicates the X-ray diffraction of ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content.From the figure, all the glass samples exhibit similar x-ray diffraction with a massive hump from 20°to 40°.Additionally, no continuous sharp peaks appear, revealing the glass system's dominance of glassy structural arrangement, and no crystalline is formed.Commonly, the absence of well-defined planes and a consistent structure arrangement on or surrounding the glass samples defines amorphous glass structures [17].Therefore, the glass samples showed a completely amorphous phase in nature.

Fourier transform infrared spectroscopy (FTIR) analysis
Figure 2 depicts the FTIR spectra of ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content, and the vibrational modes for FTIR spectra are summarized in Table 2. FTIR spectra generally reveal information about the functional groups that appear in a system, the molecular geometry, and intra-or intermolecular interactions  [18].As seen in Figure 2, the FTIR spectra of all the glass samples demonstrate a repeating pattern with five bands at ∼ 512 cm −1 , ∼ 715 cm −1 , ∼ 908 cm −1 , ∼ 1248 cm −1 , and ∼ 1337 cm −1 .The band at ∼ 512 cm −1 originated from the ZnO 4 group of symmetric stretching vibration modes [19].Likewise, the bands of 715 cm −1 and ∼ 908 cm −1 corresponded to the Si-O-Si symmetric stretching vibration [20] and Si-O-Si asymmetric stretching vibrations of SiO 4 tetrahedron [21].The appearance of these absorption bands illustrates the presence of silica in the glass bottle powder.On the other hand, the bands ∼ 715 cm −1 and ∼ 904 cm −1 were induced by Si-O-Si symmetric stretching vibration [20] and Si-O-Si asymmetric stretching vibrations of SiO 4 tetrahedron [21], respectively.These infrared absorption bands are indicated by the existence of silica in SLS glass powder.The three SiO 4 and ZnO 4 bands show no zinc silicate glass-ceramics formed, consistent with the XRD pattern, which indicated that all samples are amorphous.Furthermore, the asymmetric stretching vibrations of BO 4 units in the borate network can be identified at the wavenumber between 900 and 1000 cm −1 , which superimposes the silicate network's vibrations [22].Thus, the bands ∼ 715 cm −1 , ∼ 1244 cm −1 , and ∼ 1337 cm −1 induced B-O-B bending vibration of BO 3 triangles and B-O rings of BO 3 and BO 4 units [22], and asymmetric stretching vibration of B-O-B in BO 3 units, respectively [23].Moreover, the ∼ 715 cm −1 also ascribed Si-O-B linkages.Meanwhile, the FTIR could not discover the band of Eu 3+ in the glass samples designated 1Eu, 2Eu, and 3Eu.It is believed that this situation occurs because of a slight concentration of Eu 3 + incorporated into the glass sample and entirely dissolved in the glass samples.Khaidir et al. also reported a similar observation [24].According to the glass theory, Eu 3+ serves as a network modifier and can be attracted by the borate network.The non-bridging oxygens (NBOs) are taken up by BO 3 groups, resulting in the formation of BO 4 groups, which are negatively charged and cannot connect directly to one another.Thus, at 1244 cm −1 , BO 4 groups can join BO 3 groups and create boron-oxygen (B-O) rings [22].

Optical absorption analysis
The UV-Vis absorbance spectra of ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content from 250 nm to 1000 nm are shown in Figure 3 The transition of Eu 3+ illustrated in the UV-visible region at about 394 nm indicates the transition of 7 F 0 → 5 L 6 , attributed to the 4f-4f transition [25].This 7 F 0 → 5 L 6 transition is related to the forbidden transition by S and L selection rules but allowed by the J selection rule [26].
The mentioned transition is identical in all glass samples containing Eu 3+ dopant designated 1Eu, 2Eu, and 3Eu.Furthermore, absorbance spectra reveal the samples' amorphous nature due to the absence of welldefined absorption edges, as agreed by XRD analysis.
The absorption edges slightly shift to a longer wavelength as the Eu 3+ dopant increases.This tendency can be attributed to the glass structure's decreased rigidity due to the formation of NBOs in the glass networks [27], which FTIR proves.As the electron bonding of NBOs is less tightly packed than that of bridging oxygens (BOs), the glass networks become weaker.This may be due to the oxygen bonds' strength affecting the absorption edge of the glass system [28].

Optical band gap analysis
Kubelka-Munk's equation was utilized to evaluate the optical band gap of the samples.The UV-Vis reflectance spectra were transformed to the Kubelka-Munk function using the following equation ( 1) [29]: where R = sample's reflectance, K = Absorption coefficient, S = scattering coefficient.The Tauc equation as follows is used to determine the relationship between the band gap energy E g and the linear absorption coefficient α of a material [30]: where α = absorption coefficient, B = energy-inde pendent constant, h = Plank's constant, v = photon's frequency, and E g = band gap energy.Now, knowing that F(R) is proportional to α and that equation ( 3), where n = 1 2 and n = 2 correspond to direct allowed transition and indirect allowed transition.Then, the band gap of the glass samples was estimated by extrapolating the linear region of the Tauc plot to the x-axis, where [F(R)hv] 1/n = 0. Finally, the Tauc graph for direct and indirect allowed transition band gap is depicted in Figure 4, and the results are summarized in Table 3.
Based on Figure 4, as the Eu 3+ content increased, the optical band gap for both direct and indirect allowed transition indicates a decreasing trend, from 5.152 eV to 5.082 eV and 4.133 eV to 3.837 eV, respectively.Previous research also reported a similar observation [31].The increase in Eu 3+ content will lead to the rise in NBOs, resulting in the glass structure becoming more disordered.Eu 3+ ions, which behave as a network modifier in the glass system, have destroyed the creation of BOs.It is also reflected in alterations to the glass matrix's arrangement.In addition, incorporating Eu 3+ ions in the glass network increased the number of free electrons, decreasing the energy band gap [32].This scenario is due to a rise in matrix disorder, which expands the number of localized states within the E g [33].Apart from that, the glass samples exhibit indirect bandgap values between around ∼ 3eV to ∼ 4 eV, comparable to the semiconductor's broad bandgap values (2-4 eV) [26].As a result, the ZnO-B 2 O 3 -GB glass incorporated  Eu 3+ potentially reduced the amount of light required for lighting once likened to incandescent lamps and applied in optoelectronic devices such as LEDs.

Refractive index analysis
The refractive indexes (n) of the glass samples were determined using the Dimitrov and Sakka relation, as shown in the equation ( 4), to ascertain the uses of the synthesized glass [34].
where n is the samples' refractive index, and E opt denotes the optical band gap energy for the indirect allowed transition of the samples.The plotted refractive index of the ZnO-B 2 O 3 -GB with different Eu 3+ content is displayed in Figure 5, and the values are tabulated in Table 3.According to Figure 5 and its refractive index values, an increasing trend in the refractive index can be observed as the progression of Eu 3+ content, where the refractive index increase from 2.145 to 2.202.This rise in the refractive index could be owing to the combination of samarium oxide with higher polarizability, which produces a vast amount of oxygen ions and alters the coordination numbers [35].Abu-Khadra et al. [36] also claimed that the increased refractive index behaviour could be attributed to the structural modification due to the incorporation of Eu 3+ , whereby Eu 3+ serves as a modifier, raising the NBOs in the glass matrix.As a result, increased non-bridged oxygen will increase ionic bonding, increase the glass system's polarization, and raise the refractive index [37].In addition, the refractive index of the samples ranges from 2.145-2.202,suggesting the ZnO-B 2 O 3 -GB incorporated Eu 3+ potential for photoelectronic applications, as agreed in previous studies [38].

Urbach energy analysis
Urbach energy is the optical parameter that describes the defect states in the optical band gap region.The creation of an absorption tail in the absorption spectrum is due to these localized states of a defect in the band gap region.Hence, it is referred to as the Urbach tail, and its energy is known as Urbach energy [39].The relationship between the exponential absorption tails and the  Urbach energy is as follows [40]: where α(v) = absorption coefficient, B is the constant, hv = photon energy, and E = Urbach energy.The Urbach energy is determined by taking the reciprocal of the slope of the curves drawn between ln(α) and hv.
The plotted graph for Urbach energy of ZnO-B 2 O 3 -GB glass with different Eu 3+ content is depicted in Figure 6, and the value is illustrated in Table 3.
The Urbach energies of the samples are located within a range from 0.682 to 0.733, as listed in Table 3, appropriate for amorphous materials [41], as agreed by XRD results.The Urbach energy exhibits an increment trend with an increase in Eu 3+ content, indicating the formation of defects and growth in disorder in the glass samples.A higher Urbach energy equates to less structural stability, which means more amorphous.The rise in the Urbach energy is due to the increase in Eu 3+ dopant, where Eu 3+ serves as the glass modifier when incorporated into the ZnO-B 2 O 3 -GB glass system.It presents the possibility of elongated range order locally arising from the bonding defects, which induce localized states in the glasses, resulting in the drop in optical band gap as shown from the prior result and an increased defect concentration and width of the energy tail [42].Recently published research reported a similar tendency when Eu 3 + ion was doped with potassium titano telluroborate glasses [13].

Optical transmittance analysis
Glass transmittance is a significant characteristic in the design and development of innovative optical components.The equation ( 6) was used to determine the percentage of transmittance [43], and the transmittance spectra of the glass sample are shown in Figure 7.
where A is the absorbance.
The transmittance of all the samples over the 400-1000 nm range is approximately 70%-75%.For sample coded ZBS, 1Eu, and 2Eu, the transmittance initially steeply climbs to 70% in the visible region (400 nm-600 nm), then slightly increases to 75% in the visible and near-infrared region (600 nm-1000 nm).The sample with 3 wt.%Eu 3+ indicates the highest tance among the other sample in the visible region (400  nm -600 nm).Therefore, it reveals the ZnO-B 2 O 3 -GB glass with and without incorporation with different Eu 3+ ions have good transmittance in the visible region.

Photoluminescence excitation spectral analysis
The photoluminescence excitation (PLE) of the host, ZnO-B 2 O 3 -GB glass sample is shown in Figure 8.According to Figure 8, eleven peaks appear at 330, 353, 363, 385, 400, 413, 430, 474, 503, 520, and 536 nm, with the fixed wavelength emission at 613 nm, for the ZnO-B 2 O 3 -GB glass sample.Among these peaks, the peak at wavelength 400 nm indicates the most intense peak.These peaks indicate the electron transfer of the ZnO from the valance band (VB) to the conduction band (CB), where the VB and CB are made up of 2p oxygen orbitals and 3d orbitals of Zn, respectively [44,45].In other words, the excitation of the host is associated in the ZnO with the charge transfer transitions of O 2− → Zn 2+ [46].The PLE spectra of the ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content with the emission monitor at 612 nm is despite in Figure 9.When the Eu 3+ dopant is incorporated into the host, ZnO-B 2 O 3 -GB glass system, the transition of the Eu 3+ ions become dominant in the glass system.It can be observed that the PLE spectrum has multiple peak bandwidths ranging from 330 nm to 550 nm.The presence of excitation peaks correspond to the transition 7 F 0 → 5 H 6 (330 nm), 7 F 0 → 5 D 4 (352 nm), 7 F 0 → 5 L 7 (385 nm), 7 F 0 → 5 L 6 (400 nm), 7 F 0 → 5 D 3 (414 nm), 7 F 0 → 5 D 2 (473 nm), 7 F 0 → 5 D 1 (502, 520, 536 nm) [47,48].The excitation spectra include the near ultraviolet and blue light regions; therefore, the materials could be effectively excited by the near-ultraviolet and blue LED chips [49].Among the peaks, the major excitation peak is located at 400 nm, similar to the host.Hence, 400 nm is chosen as the excitation wavelength to study the PL emission of the glass sample to emit intense reddish-orange emission.

Photoluminescence emission spectral analysis
Figure 10 indicates the glass samples' photoluminescence (PL) emission spectrum excited at 400 nm.From Figure 10, the glass sample coded ZBS, without Eu 3+ incorporated into the ZnO-B 2 O 3 -GB glass system, indicates three emission peaks at 530 nm (green), 574 nm (yellow), and 707 (red).The green emission of the ZnO-B 2 O 3 -GB glass could be due to the zinc vacancies inside the ZnO [50].Generally, the defect states that occur in ZnO are zinc vacancies (V Zn ), oxygen vacancies (V O ), zinc interstitial (Zn i ), oxygen interstitial (O i ), and oxygen antisite (O Zn ) [46].Since zinc vacancies are the deep acceptors, they are more likely to be where the green luminescence in ZnO originates [51].Furthermore, the SiO 2 matrix could have reflected the UV emission.There are two possible mechanisms by which the surface interaction between ZnO particles and the SiO 2 matrix could increase the UV-emission of the ZnO-B 2 O 3 -GB glass sample.First, the SiO 2 matrix altered the surface properties of ZnO particles, leading to a decrease in the density of surface dangling bonds and concentrations of O 2− ions in the Zn-O-Si.It decreased the likelihood of non-radiative ions and visible emission, which enhanced UV emission.Second, the surface interaction between ZnO and SiO 2 could influence the UV-photoluminescence enhancement by developing interface states where the carrier can be trapped and recombined to emit UV light [52].Meanwhile, the green region (530 nm) appears in the ZnO-B 2 O 3 -GB glass related to the transition from the conduction band to oxygen vacancies (CB → V O ) [53].The zinc interstitial transition (Zn i + → V Zn − ) gives the yellow emission at 574 nm [54].On the other hand, the emission of 707 nm (red) is due to the transition from the conduction band to oxygen interstitials (CB → O i ) [53].The ZnO-B 2 O 3 -GB glass's green, yellow, and red emissions were thereby affected by a defect in  the ZnO particle and aided by SiO 2 .In the meantime, the schematic band structures diagram of ZnO in the ZnO-B 2 O 3 -GB glass system is shown in Figure 11.
In contrast, when the glass samples are incorporated with Eu 3+ ions, several new emission spectra start to appear due to the presence of Eu 3+ ions.Moreover, the PL emission band trend shifts to a higher wavelength as the Eu 3+ dopant increases.Therefore, when the Eu 3+ dopant increases up to 3 wt.%, the emission band emerges at 578 nm (yellow), 592 nm (orange), 612 nm (reddish-orange), 652 nm (red), 699 nm (red), and 734 nm (red).Meanwhile, once excited at 400 nm, the Eu 3+ ions will originally be excited from 7 F 0 to the 5 L 6 state.Then, the Eu 3+ ions relax to the 5 D 2 state by populating it and subsequently populating the low-lying 5 D 1 and 5 D 0 energy levels non-radiatively, with emission of transitions from metastable state 5 D 0 to 7 F J , where J = 0 to 5 [47,55].The energy transition 5 D 0 → 7 F J (J = 0, 1, 2, 3, 4, 5) designated to 578, 592, 612, 652, 699, and 734 nm, respectively.The energy level diagram for the transitions of Eu 3+ in the ZnO-B 2 O 3 -GB glass system is depicted in Figure 12.The dipole emission transition 5 D 0 → 7 F 0 (578 nm) is environmentally sensitive and is forbidden according to parity selection rules, where J = 0 and the transition from J = 0 → 0 indicate forbidden.Additionally, the ground state 7 F 0 and the first excited state 5 D 0 are non-degenerate, regardless of the symmetry [55].In the meantime, the transition 5 D 0 → 7 F 1 (592 nm) belongs to the dipole (MD) transitions which obey the selection rule shown in Table 4, where J = ± 1.It is independent of the host matrix, which suggests that its intensity is unaltered by the local symmetry [56].The 5 D 0 → 7 F 2 (612 nm) is attributed to magnetic dipole (MD) transitions, which follow the selection rule [57] shown in Table 4, where J = ± 2. It is hypersensitive and highly influenced by the symmetry of the Eu 3+ ions' local environment.The electric dipole transition is only possible if the Eu 3+ ion is in a location without an inversion centre [58].The 5 D 0 → 7 F 3 (652 nm) have transitions with a mixed character (MD and ED) owing to J-mixing, aided by the host matrix's significant crystal-field effects.It reveals that the Eu 3+ ions are asymmetrically located in the matrix.Furthermore, the 5 D 0 → 7 F 4 (699 nm) induced electric dipole transition due to J = ± 4, and 5 D 0 → 7 F 5 (734 nm) belong forbidden owing to the J-mixing effect between multiplets.The analysis of emission transitions performed by the published findings [37,38,40] and the summarized emission transition are listed in Table 5.Based on Figure 11, the reddish-orange emission at 612 nm ( 5 D 0 → 7 F 2 ) indicates the most intense emission among all the emissions.Moreover, the 5 D 0 → 7 F 2 transition is more robust than the 5 D 0 → 7 F 1 , implying that Eu 3+ is found in low symmetry sites.Therefore, the intense emission at 612 nm suggests that the Eu 3+ incorporated ZnO-B 2 O 3 -GB glass potential to be reddish-orange emitting materials [59].Indeed, the intensity of the emission increase as progression on the Eu 3+ dopant, and the sample with 3 wt.%Eu 3+ dopants indicate the highest emission intensity among the other content of Eu 3+ dopants in this work.Thus, it can be said that the optimum dopant of Eu 3+ incorporated into the ZnO-B 2 O 3 -GB glass system is 3 wt.%among the other Eu 3+ dopants content (0, 1, and 2 wt.%) in current work.

CIE 1931 chromaticity analysis
The Commission International d'Eclairage (CIE) 1931 is used to analyze the dominant emission colour of Eu 3+ incorporated into the ZnO-B 2 O 3 -GB glass system.The CIE 1931 diagram is a widely acknowledged technique for representing any colour's component using the primary colours: red, blue, and green [56].The CIE 1931 chromaticity is shown in Figure 13.The chromaticity coordinates, dominant wavelength, CCT, and colour purity of the glass samples are listed in Table 6.Based on Figure 13, the CIE coordinate of ZBS found at (0.4692, 0.5071), which falls in the yellow-orange region, while its dominant wavelength is 575.1 nm.On   the other hand, when the Eu 3+ is incorporated into the ZnO-B 2 O 3 -GB glass system, the chromaticity coordinates are located in the reddish-orange region.The CIE coordinates (0.5687, 0.4304), (0.5741, 0.4251), and (0.5790, 0.4201) belong to 1Eu, 2Eu, and 3Eu glass samples, respectively.Meanwhile, the dominant wavelength increased from 575.1 nm to 590.7 nm, indicating that the samples shifted from yellow to reddish-orange.Figure 14 shows the ZnO-B 2 O 3 -GB glass sample under UV lamp excites at 365 nm wavelength.The calculated CIE coordinates for Eu 3+ incorporated ZnO-B 2 O 3 -GB glass are near the Amber LED NSPAR 70BS produced by Nichia Corporation (0.570, 0.420) [60].Moreover, Cao and the coworker also reported a similar CIE coordinate at (0.5732, 4262) in Ca 3 La 6 Si 6 O 24 :Eu 3+ phosphor [48].The correlated colour temperature (CCT) is typically required to evaluate the quality of light emitted by the glasses.The calculated CCT value dropped from 3220 K (ZBS) to 1673 K (3Eu) when the Eu 3+ incorporated ZnO-B 2 O 3 -GB glass.The CCT value, ∼ 1600 K, is less than the fluorescent tube (3935 K) [33], and it indicates the samples with Eu 3+ dopant have bright reddish-orange emission.Moreover, the samples' colour purity reveals a high value, at 99%, implying that they meet the basic criteria for field emission displays.Thus, the excellent colour purity of the Eu 3+ incorporated ZnO-B 2 O 3 -GB glass suggests it is ideal for reddish-orange LED applications.

Conclusion
To sum up, the zinc-borosilicate glass incorporated with Eu 3+ derived from the waste glass bottle was successfully synthesized via the conventical melt-quenching method.XRD and FTIR proved amorphous in the glass sample.The absorption spectra imply the transition of Eu 3+ present in the UV-visible region at ∼ 394 nm attributed to the 4f-4f transition.The optical band gap for direct and indirect band gap reveals a decreasing trend as the Eu 3+ dopant increases.The increase in Eu 3+ dopant led to the rise in NBOs, resulting in the glass structure becoming more disordered.Additionally, the refractive index and Urbach energy trend increase with increasing the Eu 3+ content.Besides, the emission at 612 nm ( 5 D 0 → 7 F 2 ) in the PL spectrum indicates the most intense emission among all the emissions when excited at 400 nm.This work's optimal content for Eu 3+ incorporated ZnO-B 2 O 3 -GB glass is 3 wt.%among the other Eu 3+ dopants content (0, 1, and 2 wt.%), which gives the highest emission intensity.In the meantime, the CIE chromaticity coordinates reveal the samples incorporated with Eu 3+ located in the reddishorange region.Therefore, the findings suggest that the ZnO-B 2 O 3 -GB glass potential be utilized in optoelectronic applications such as reddish-orange LED lighting.

Figure 5 .
Figure 5. Refractive index of the ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content.

Figure 6 .
Figure 6.Urbach energy of the ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content.

Figure 9 .
Figure 9. PLE spectra of the ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content.

Figure 10 .
Figure 10.PL emission spectra glass samples excited at wavelength 400 nm.

Figure 11 .
Figure 11.Schematic band structures diagram of ZnO in the ZnO-B 2 O 3 -GB glass system.

Figure 14 .
Figure 14.The ZnO-B 2 O 3 -GB glass sample under UV lamp excites at 365 nm wavelength.

Table 1 .
The glass sample's composition.

Table 2 .
Vibrational mode for FTIR spectra of ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content.

Table 3 .
Optical band gap energy for direct and indirect allowed transition, refractive index, and Urbach energy of the ZnO-B 2 O 3 -GB incorporated with different Eu 3+ content.

Table 5 .
Emission transition and its colour for the designated emission wavelength.

Table 6 .
Chromaticity coordinates, dominant wavelength, CCT, and colour purity of the glass samples.