This proposal is part of a long-range program aiming at determining the stable charge-state configurations, site and impurity energy levels (donor and/or acceptor) of hydrogen in widegap oxides with important technological applications, by means of the analogy with muonium. We now propose to adress in detail two representative systems: (i) sapphire (Al2O3), where a long-standing unresolved problem subsists regarding the low-temperature conversion of muonium, which we believe may be conveniently adressed by RF-muSR; (ii) tellurium oxide (TeO2), where prospective measurements indicate the presence of muonium dynamics Prospective measurements on Y2O3 are also proposed. (N.B.: This proposal is a modified version of the previously approved proposal RB 910470, which could not be run.)