Conversion of constant-wave near-infrared laser to continuum white light by Yb-doped oxides

White light generation is of particular interest for artificial lighting as well as spectroscopy. Here, we report the conversion of constant-wave (CW) near infrared (NIR) laser to continuum white light emission by Yb-doped oxides. The white light generation occurs by irradiating the oxide powders with the NIR laser at room temperature and atmospheric pressure. The excitation powder dependence of the emission intensity demonstrates an evident threshold, above which the brightness increases abruptly. By using an infrared thermal camera, it is found that the above-threshold rise of emission intensity is accompanied by the rapid rise of sample temperature, and the lowest temperature of white light emission is about 630 degrees C, which is far lower than the spectrally derived blackbody radiation temperature (>2000 degrees C). In addition, the results show that the peak of the emission is close to the excitation laser wavelength (940 nm), and the spectral width grows with excitation power and sample temperature. These observations lead us to conclude that the white light is associated with the thermally enhanced spectral continuum generated by nonlinear optical processes, such as resonant Raman scattering.