## 1 Introduction  
New materials, hetero-structures, hetero-junctions, and doped single crystal have been the subject of numerous studies to produce optoelectronics devices emitting from blue to near-IR region [1]. Recent applications such as high-density optical memories, display devices, and biological applications require solid-state semiconductor laser and light emitting diodes (LED) emitting in the blue and green wavelengths. Others, for example, the LED of high efficiency for illumination, require high as well as low wavelengths to illuminate inner spaces. The possible semiconductors that emit light in these wavelengths are the ones of the II-VI semiconductor family. These materials have direct gap edge of energy capable of emitting photons with a wavelength less than 500 nm. Investigations for laser devices with materials such as GaN and ZnSe have had a tremendous progress in the last thirty years. In 1991, a ZnCdSe/ZnSe quantum well laser diode successfully demonstrated a pulsed operation at room temperature [2]. The first solid-state semiconductor blue-green laser and light emitting diode (LED) were built in 1991-1992 using wide band gap II-VI semiconductors with a ZnSe-based single quantum well structure [3, 4]. A GaN/AlGaN double-heterstructure has shown optically a pumped lasing in the UV region at room temperature [5]. High efficiency InGaN/GaN double-heterostructure LEDs have also been obtained [6]. Other materials and technologies to produce compact diode-pumped Nd: LuVO\({}_{4}\) solid state lasers have been studied [7] as well as the high-efficiency nitride semiconductor blue lasers and light emitting diodes [8]. ZnSe is chemically stable metal chalcogenide, which possesses many advantages, making it an important optoelectronic material. It has useful electronic properties such as a wide and direct bandgap, low electrical resistivity, and n-type conductivity. Regarding optical properties, it has a broad transparency from visible to mid infrared wavelengths, high refractive index, low dispersion, and high photosensitivity. From the other side,the trivalent rare earth ions are particularly useful because they produce additional lines and enhance the intensity of the emission spectra because f-electron absorption transitions are much weaker than those of the d electrons. This allows for the use of much higher active ion concentrations without complications from extensive self-absorption or excitation depletion. Recently several papers have reported on the luminescence of II-VI semiconductors doped with Tb\({}^{3+}\), Sm\({}^{2+}\), Eu\({}^{3+}\)/Eu\({}^{2+}\), or Er [8; 9] particularly on the luminescence of ZnSe:Eu\({}^{3+}\) and ZnSe:Yb [10; 11]. Moreover, the co-doping with two rare earths gives the possibility of optical pumping between the f electron quantum levels of one rare earth to the other. Additionally, Yb\({}^{3+}\) has a relatively simple energy diagram presented by one excited state \({}^{2}\)F\({}_{5/2}\) and a ground \({}^{2}\)F\({}_{7/2}\) state lying \(\approx\) 1.2 eV below, absence of the line widening, and absorption on the excited state [12]. Therefore, the energy level configuration of ZnSe: Eu\({}^{3+}\)/Yb\({}^{3+}\) may generate transitions, which allow for a wider range of wavelengths in the photoluminescence spectrum. However, there have not been any reports on the photoluminescence properties of ZnSe co-doped with Eu\({}^{3+}\) and Yb\({}^{3+}\). In this work, high quality single crystals were doped and co-doped with Eu\({}^{3+}\)/Yb\({}^{3+}\) rare earths in order to obtain semiconductors with very high photoluminescence in the visible and near infrared region. The luminescence spectra of these materials give multiple intense and sharp emission lines. The material was characterized using photoluminescence and UV-Vis techniques in order to obtain their photoluminescence and absorption properties.