his paper reports the frequency upconversion and cooperative luminescence in YBO3:Yb3+-Er3+ sample. After cw diode laser excitation, at 980 nm, three clear bands were observed at around 650, 545 and 484 nm, corresponding to red, green and blue emissions, respectively. The bands centred at 650 and 545 nm can be attributed to upconversion emissions from Er3+ ions. Mechanisms of energy transfer upconversion and excited-state absorption of pump radiation are proposed in order to explain these radiative transitions. The blue emission at 484 nm is analysed with the aim to elucidate if it can be attributed to cooperative luminescence from Yb3+-pairs. Finally, the color diagram is presented so as to study the color purity of the sample.
