## 2 Results and Discussion
That means the quenching is directly proportional to the activator ion concentration, which indicates that the concentration quenching is caused by the energy transfer among the nearest-neighbor Eu\({}^{2+}\) ions in the Sr\({}^{4-4x}\)Si\({}_{3}\)OsCl\({}_{4}\): 4\({}_{x}\)Eu\({}^{2+}\) phosphors. The excitation spectra of the phosphors Sr\({}_{3.90-4y}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 4\(y\)Bi\({}^{3+}\) (\(y=0.00\), 0.05, 0.10, 0.15, 0.20) by monitoring emission 490 nm is shown in Figure 4. With the doping of Bi\({}^{3+}\), the shoulder peak around 400 nm is broadened with a little red shift, and the excitation intensity is enhanced. When the content of Bi\({}^{3+}\) is 0.10, the excitation intensity is the strongest. Figure 5 is the emission spectra of Sr\({}_{3.90-4y}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 4 yBi\({}^{3+}\) (\(y=0.00\), 0.05, 0.10, 0.15, 0.20) under 320 nm excitation. The broad emission from 400 nm to 600 nm is due to the 4t\({}^{6}\)5d\({}_{1}\to 4t^{7}\) transition of Eu\({}^{2+}\) ions. The strongest peak is located at 490 nm. The concentration dependence of the relative integral emission intensity of Sr\({}_{3.90-4y}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 4 yBi\({}^{3+}\) is shown in the inserted figure of Figure 5. When the content of Bi\({}^{3+}\) is at 0.10, its emission intensity is the strongest, and its intensity is about 1.3 times higher than that of Sr\({}_{3.90}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\) without Bi\({}^{3+}\). This result is consistent with their excitation spectra. Bright blue-green light can be observed from Sr\({}_{3.50}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 0.40 Bi\({}^{3+}\) under 365 nm light excitation (seeing the inset of Figure 5). The compositions Sr\({}_{3.90-4y}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 4 yBi\({}^{3+}\) are not charge balanced and have a slight excess of positive charge because of Bi\({}^{3+}\) substituting Sr\({}^{2+}\). The excess charge could be compensated by a number of mechanisms, for example, cation vacancies, varying slightly O contents, _etc._[20]. In this series of phosphors, this kind of substitution did not influence the emission spectra shapes of Sr\({}_{3.90-4y}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 4 yBi\({}^{3+}\) (seeing Figure 5). Figure 6 shows the electroluminescence (EL) spectra of the intense blue-green LED fabricated with Sr\({}_{3.90}\)Si\({}_{3}\)O\(\bullet\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\) and Sr\({}_{3.50}\)Si\({}_{3}\)O\(\bullet\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 0.40 Bi\({}^{3+}\) under 20 mA current excitation. The emission band at \(\sim\)400 nm is attributed to the emission of LED chip and the broad band from 430 nm to 600 nm is due to the emission of the phosphor. Comparing with curve \(a\), the ratio of LED chip emission to phosphor emission in curve \(b\) is smaller. The result indicates phosphor Sr\({}_{3.50}\)Si\({}_{3}\)O\(\bullet\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 0.40 Bi\({}^{3+}\) can more efficiently absorb the emission of LED chip, and exhibit stronger blue-green emission, compared with Sr\({}_{3.90}\)Si\({}_{3}\)O\(\bullet\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\). Bright blue-green light is observed from these two LEDs by the naked eye. This result is in accordance with their emission spectra. Their CIE chromaticity coordinates are calculated to be \(x\) = 0.169, \(y\) = 0.356, and \(x\) = 0.170, \(y\) = 0.362, respectively. Figure 6: Electroluminescence (EL) spectra of the blue-green light-emitting-diodes (LEDs) based on (**a**) Sr\({}_{3.90}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\) and (**b**) Sr\({}_{3.50}\)Si\({}_{3}\)O\({}_{8}\)Cl\({}_{4}\):0.10 Eu\({}^{2+}\), 0.40 Bi\({}^{3+}\) under 20 mA current excitation; the inserted figures are the images of these two LEDs.