O objetivo principal deste trabalho é o estudo por ressonância paramagnética eletrônica das impurezas Cr3+, Er3+ e Mn3+ no monocristal Ca3Ga2Ge3O12 (denominado CGGG) nas freqüências de 1.3, 10 e 34 GHz e nas temperaturas de 4,2K a 300K. O Hamiltoniano de spin para o Cr3+ alojado no sítio octaédrico com simetria C Cr3i é dado por: H = &#946[g&#8869 (HxSx + HySy) + g&#8204HzSz] + D (S2z - 1/3 S (S+1). Os parâmetros do Hamiltoniano de spin para o íon Cr3+ em baixas concentrações são: g&#8204 = 1,9727 &#177 0,0003, g&#8869 = 1,9617 &#177 0,0008 e D = 16,20 &#177 0,02GHz para CGGG dopados com o íon Cr3+. Os cristais CGGG, dopados com Er3+ e Cr3+, apresentaram os seguintes parâmetros g&#8204 = 1,9662 &#177 0,0003, g&#8869 = 1,9617 &#177 0,0008 e D = 15,82 &#177 0,02GHz. Os parâmetros do Hamiltoniano de spin efetivo para o íon Er3+ alojado no sítio dodecaédrico e com simetria D2 são: gx = 2,690 &#177 0,0005, gy = 4,095 &#177 0,005 e gz = 5,082 &#177 0,005. Os centros paramagnéticos Mn2+ produzidos em cristais dopados com Cr3+, irradiados com raios X, à temperatura ambiente, apresentam o fator-g isotrópico, g = 2,0066 &#177 0,0001 e a constante de interação hiperfina A = 90 Gauss. Medimos, também as dependências das larguras de linhas com a temperatura, nas três bandas e para banda X medimos nas temperaturas de 4,2K até 300K

In this work was studied the Electron Paramagnetic Resonance (RPE) of the impurities Cr3+, Er3+ and Mn3+ in Ca3Ga2Ge3O12 single crystals (Known as CGGG) at frequencies of 1.3, 10 and 34 GHz in the temperatures range 4,2K to 300K. Spin Hamiltonian for the Cr3+ íons, located at octahedric position with symetry Cr3i is given by: H = &#946[g&#8869 (HxSx + HySy) + g&#8204HzSz] + D (S2z - 1/3 S (S+1). The relevant parameters for CGGG lightly dopped with Cr3+ as determined from the EPR spectra are: g&#8204 = 1,9662 &#177 0,0003, g&#8869 = 1,9617 &#177 0,0008 and D = 15,82 &#177 0,02GHz. CGGG crystals simultaneously dopped with Er3+ and Cr3+ shown the following parameters: g&#8204 = 1,9662 &#177 0,0003, g&#8869 = 1,9617 &#177 0,0008 e D = 15,82 &#177 0,02GHz. Effective spin Hamiltonian parameters for Er3+ íon, located at dodecahedric position and with symetry D2, are: gx = 2,690 &#177 0,0005, gy = 4,095 &#177 0,005 e gz = 5,082 &#177 0,005. Paramagnetic centers Mn2+ produced in Cr3+ dopped crystals, X-ray irradiated, at room temperature, shown the isotropic g-factor g = 2,0066 &#177 0,0001 and the hyperfine interaction constant A = 90 Gauss. Also, was measured the temperature dependence of the line width in the three frequency bands, in the range of liquid nitrogen to room temperature. In the case of the X-band, the measurements were extended to lower temperatures, 4.2K to 300K