Upconversion,avalanche effect and controlled optical switching in Yb3+, Ho3+ co-doped Ca12Al14O33 phosphor

In the present work, Yb³⁺/Ho³⁺ co-doped Ca₁₂Al₁₄O₃₃ phosphor has been synthesized and upconversion (UC) fluorescence has been studied by pumping the sample with 976 nm radiation. In addition to a strong UC fluorescence due to Ho³⁺, an avalanche effect is also observed with an increase in input laser power. At a certain threshold power, optical switching (a switching in emission intensity of different transitions) behavior is observed whose response time has been estimated to be of the order of milliseconds. A substantial heat generation inside the host matrix due to electron–phonon coupling (non-radiative relaxations) of the rare-earth ion and the host matrix has been assigned responsible for the switching phenomenon. The heat generation has been confirmed and estimated using fluorescence intensity ratio (FIR) method.