Improvement of phosphorescence properties of zinc borosilicate glasses with the addition of rare earth and transition elements

The word of luminescence defined as a phosphor which refers to the stimulation of materials with different types of external energy without heating; moreover, this energy converted into electromagnetic radiation and emitted as a light. The electromagnetic waves might be in the not only visible region of 400-700 nm but also ultraviolet and infrared regions. Luminescence can be excited by various types of energy sources and named as according to using energy sources. When material is excited by electromagnetic radiation, emission of light from a material is called as photoluminescence. A molecule or an atom absorbs electromagnetic radiation and electron is excited from ground state to higher energy states. When electromagnetic radiation removed, excited electron returns to ground state by emitting a light. This phenomenon defined as photoluminescence. Photoluminescence can be classified into two categories according to lifetimes of emission: fluorescence and phosphorescence. Emission of light takes place from electronically excited singlet state is called fluorescence, while emission of light takes place from electronically excited triplet states and light emission persists after the removing of excitation is called phosphorescence. Phosphors materials are consist of host material with suitable crystal structure and activator. Activator which is small amount of intentionally incorporated impurity atoms distributed in the host material. Transition metals or rare earth elements are used as an activator; moreover, they disturb the band structure of host material by creating luminescence center. Intensity and afterglow time of phosphorescence materials are improved with the addition of these elements. Different types of phosphor materials were produced according to the host material and dopants. In this way, different wavelengths and different colors are obtained as a result of interaction with host material and dopants. Although ceramic based phosphors are known as popular for long lasting phosphorescence, glass phosphors are very versatile materials due to their transparency, homogeneity and can be easily fabricated to various forms. High quantities of rare earth can be doped into the glass matrix thanks to their flexible lattice structure. Also, high concentrations of dopants provide the formation of the luminescence and trap centers. When transparent glass is excited, released electromagnetic radiation is transmitted; on the other hand, opaque glass reflected the incident light. Therefore, it is important to obtain transparent glass with high transmittance which allows the emission of light without creating barrier in phosphorescence applications. Phosphorescence properties of glass materials are gained by three different methods. Phosphor pigments are added into the glass blend or covering the surface of the glass materials with the glazing technique. In the first two methods, forming of porosity and crystallization of glass during melting is a important problem in order to gain homogeneous structure; moreover, non-homogenous distribution of phosphor pigments cause spot and localized emission. In the last method, glass blend is produced with doping of suitable rare earths and transition metals. In this study, phosphorescence properties of zinc borosilicate glasses were improved with the addition of rare earth and transition elements. 55ZnO-25B2O3-20SiO2 glass composition was determined and small amount of dopant material (Tb, Sm, and Mn) was added. After deciding the dopant concentration, rare earth elements were added as second additive (co-dopant) in order to develop intensity and afterglow time of phosphorescence. Heat treatment was applied at different temperatures and excess boric acid has been added to glass composition to investigate the effects of these parameters on phosphorescence properties of glass samples. A change in phosphorescence properties were observed by adding sodium oxide instead of zinc oxide to the host glass in order to gain phosphorescence property to the sodium borate glasses. Mixed batches were melted in platinum crucibles at 1500 °C for 30 minutes. The melt was quenched to room temperature to get transparent glass. In addition, XRD, DTA, phosphorescence spectrophotometer and light transmission characterization methods were performed for phase analysis and phosphorescence properties of obtained glasses. Zinc borosilicate glasses doped with samarium (55ZnO-25B2O3-20SiO2-xSm2O3) were prepared; moreover, optimal phosphorescence intensity of zinc borosilicate glass was typically obtained with 0.4 % mole Sm2O3 concentration. However, when UV light was removed, emission of light did not observe with naked eye. There was no persistency although Sm doped glasses have phosphorescence properties. In 55ZnO-25B2O3-20SiO2-xMnO glass composition which MnO was used as a dopant, the phosphorescence intensity of glass was as low as invisible when exposed to UV light. Therefore, 0.1 mol % Sm2O3 was used as co-dopant for improving intensity of phosphorescence of Mn doped zinc borosilicate glass. Compared with the glasses solely activated by Mn2+, when the Sm3+ ion was co-doped, the red long lasting phosphorescence of the samples was largely improved in both brightness and afterglow time. Also, optimal MnO concentration was determined 0.18 % mol. In addition, various amount of Sm2O3 was doped to 0.18 % mol MnO concentration zinc borosilicate glasses for investigating of intensity and afterglow time. According to the results, 0.4 mol % Sm2O3 co-doped glass has optimum phosphorescence intensity and afterglow time. The compositions of the glass samples were prepared 55ZnO-25B2O3-20SiO2-0.18MnO-0.4Sm2O3-xH3BO3 in order to investigate effect of boric acid. Boric acid was added to the system successfully up to 10 mol%, which was increased the intensity while did not influence the afterglow time of glasses. However, when boric acid was added to system above 15 mol %, glasses lost their transparency. Heat treatment was applied at 600, 700 and 800 °C. Heat treatment at 600 °C was increased the phosphorescence intensity of glass but it did not affect the afterglow time. According to XRD analysis at 800 °C glasses turned into glass ceramic and lost their transparency. When Eu3+ was added as a co-dopant to the Mn2+ doped zinc borosilicate glasses, phosphorescence intensity of glasses were increased; on the other hand, UV light was removed emission of light did not observe with naked eye and there was no persistency. In ZnO-25B2O3-20SiO2-xTb2O3 glass composition which Tb2O3 was used as a dopant, the phosphorescence intensity of glass was increased with the dopant concentration hence afterglow time was decreased. The compositions of the glass samples prepared were 55ZnO-25B2O3-20SiO2-0.18MnO-0.7Tb2O3-xH3BO3 in order to investigate effect of boric acid. Boric acid was added to the system successfully up to 10 mol%, which is increased the intensity while do not influence the afterglow time of glasses. However, when boric acid was added to system above 15 mol %, glasses loss their transparency. In addition, heat treatment at 600 °C was increased the phosphorescence intensity of glass but afterglow time was not affected. Tm, Gd, Ce and Dy was added as co-dopant to Tb doped zinc borosilicate glass. Phosphorescence intensity of glasses was increased with addition of Tm3+, was decreased with addition of Gd3+ and Ce3+. Dy3+ was caused the loss of the phosphorescence property of zinc borosilicate glass. According to light transmission measurement, boric acid was decreased the transmittance but heat treatment at 600°C was increased the transmittance of light. In (55-x)ZnO-25B2O3-20SiO2-xNa2O-0.35Tb2O3 glass composition which Na2O was used instead of zinc oxide. Sodium oxide was added to the system successfully up to 10 mol%, which was increased the phosphorescence intensity.