Study On The Preparation And Properties Of Rare Earth Ions Doped Luminescence Glasses For LED Applications

In recent years,light emitting diodes?LEDs?have been regarded as a new generation of lighting source due to their considerable advantages in energy-saving and environmental protection,long lifespan,high efficiency,anti-bad environment,wide spectral range,compact size and so on.The W-LED fabricated by combining a blue chip with a yellow YAG: Ce phosphor has been commercialized due to the advantages of low cost and high brightness.However,this kind of W-LEDs have lower color rendering.The brightness of the phosphor decreases with the temperature rise of the working device and fluorescent powder coating uniformity is difficult to realize.Compared with the phosphors used in W-LEDs,luminescence glasses are excellent candidates to prepare W-LEDs because glasses have the advantages of excellent uniformity,high transparency,easy to be processed into various shapes,low production cost and high thermal stability.They also can be directly packaged with a semiconductor chip without epoxy resin to fabricate LED device.We investigate the rare earth ions doped luminescence glasses for LEDs in this paper.The oxyfluoride borosilicate glasses are important materials with excellent chemical stabilityand high mechanical strength.They as also possess lower phonon energy environment for luminescence ions,thus can effectively improve the luminous intensity.The aluminoborosilicate glasses have the advantages of low synthesis temperature,high transmission,excellent thermal and chemical stability,also can improve the solubility of rare earth ions.We choose oxyfluoride borosilicate glasses and aluminoborosilicate glasses as glass matrixs to prepare a series of Ce-Dy/Ce-Dy-Eu doped/codoped glasses.These glasses are studied via X-ray diffraction?XRD?,optical absorption,photoluminescence?PL?,Fourier transform infrared?FT-IR?spectra,color coordinate and correlated color temperatures?CCTs?.The main research contents and the result are as follows:In the Ce³⁺ ions single doped and Ce³⁺-Dy³⁺ ions codoped oxyfluoride borosilicate glasses,the absorption and emission bands of Ce³⁺ ions move to the longer wavelengths with increasing excitation wavelength?298 nm ? 350 nm?,increasing Ce³⁺ concentrations and decreasing B₂O₃ and Al₂O₃ contents in the glass compositions.In the Ce-Dy-Eu doped aluminoborosilicate glasses and oxyfluoride borosilicate glasses,the reduction of Eu³⁺ to Eu²⁺ occurs and the decrease of the optical basicity of glass matrix leads to the enhancement of Eu³⁺?Eu²⁺ conversion.The red shift of emission bands of Ce³⁺ ions occurs with increasing excitation wavelength?350 nm?395 nm?,increasing ratio of B₂O₃/SiO₂ and Al₂O₃/SiO₂ in the glass compositions and the precipitation of CaF2 crystals.Meanwhile,the precipitation of CaF₂ crystals in the glass matrix can greatly increase the relative intensity of the emission spectra.The effective energy transfer of Ce³⁺?Dy³⁺,Ce³⁺?Eu³⁺,Ce³⁺?Eu²⁺,Eu²⁺?Dy³⁺,Eu²⁺?Eu³⁺ could take place among Ce³⁺,Dy³⁺,Eu³⁺ and Eu²⁺ ions.The excitation wavelength,glass matrix composition and glass crystallization can influence the color coordinates and correlated color temperatures of the as-prepared glasses.In the Ce-Dy / Ce-Dy-Eu codoped glasses,we obtained the chromaticity coordinates which are much closer to the ideal white light?x = 0.33,y = 0.33?.