A chip scale packaging (CSP) light-emitting device including a light-emitting semiconductor die and a layer-by-layer photoluminescent (PL) structure disposed on the light-emitting semiconductor die is disclosed. The PL structure includes a second PL layer and a first PL layer disposed over the second PL layer, wherein the first PL layer functions as a photoluminescent layer and a barrier layer protecting the second PL from ambient oxygen and moisture. The first PL layer includes a less-moisture-sensitive PL material dispersed within a first polymer matrix material, whereas the second PL layer includes a moisture-sensitive PL material dispersed within a second polymer material. With these arrangements, the outermost first PL layer comprising the less-moisture-sensitive photoluminescent material functions as a wavelength-conversion layer and also serves as a barrier layer protecting the inner second PL layer comprising the moisture-sensitive photoluminescent material from ambient oxygen and moisture. Thus degradation of moisture-sensitive PL material can be reduced.